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ANA LUISA TONDIN MENGARDO
Subsídios para o manejo da invasão biológica de
uma palmeira em áreas de Mata Atlântica
São Paulo
2011
2
ANA LUISA TONDIN MENGARDO
Subsídios para o manejo da invasão biológica de
uma palmeira em áreas de Mata Atlântica
Subsidies to ecological management of the biological
invasion by a palm tree in Atlantic forest areas
Dissertação apresentada ao Instituto de Biociências da Universidade de São Paulo, para a obtenção de Título de Mestre em Ciências, na Área de Ecologia. Orientador(a): Profª Drª Vânia Regina Pivello
São Paulo
2011
3
Ficha Catalográfica
Mengardo, Ana Luisa Subsídios para o manejo da invasão biológica de uma palmeira em áreas de Mata Atlântica 88 páginas Dissertação (Mestrado) - Instituto de Biociências da Universidade de São Paulo. Departamento de Ecologia. 1. Invasão Biológica 2. Palmeiras 3. Ecologia. I. Universidade de São Paulo. Instituto de Biociências. Departamento de Ecologia.
Comissão Julgadora:
________________________ _______________________ Prof(a). Dr(a). Prof(a). Dr(a).
__________________________ Prof(a). Dr.(a). Vânia Regina Pivello
Universidade de São Paulo Orientadora
4
Ao Piu e à Su...
5
“Minha terra tem palmeiras
Onde canta o sabiá!”
Gonçalves Dias
“Valeu a pena? Tudo vale a pena se a alma não é pequena...”
Fernando Pessoa
6
Agradecimentos!
À Vânia Pivello, pela orientação, confiança, paciência, apoio e amizade.
Por sempre me apresentar a novas oportunidades. E por ser, além de
orientadora, uma segunda mãe!
À FAPESP, pelo apoio financeiro concedido;
Ao Mingau, pela parceria ao longo desses anos, pelo incentivo e
companhia, transformando a rotina em milhares de pequenos momentos
incríveis... e por todas as boas idéias que já tivemos e ainda teremos!
À minha família: aos meus pais, que me deram base, apoio e incentivo
incondicionais; à Jubis e ao Dan, por tentarem entender a pós‐graduação e esse
estilo de vida! Não seria a mesma sem esses quatro Mengardos!
Ao Cris, pelo trabalho em conjunto e pelas excelentes conversas dentro da
mata aos domingos de manhã!
À família LEPaC: Alessandra, Ale e Lê (meus “irmãos mais velhos”), Beth,
Mari, Tablita, Imma, Flávio, Dani e Thaís. Obrigado pela melhor rotina de
trabalho, e também pelos momentos além do expediente!
Aos amigos da Eco: Du, Marcel, Ruggero, Gustavo, Jomar e Luis. E, é
claro, às damas mais do que queridas do LabVert: Má, Laura, e Hamanda –
partes da família também!
Aos professores do IB, que de alguma maneira contribuíram para essa
Dissertação: Jean Paul Metzger, Sergio Tadeu Meirelles, Marcio Martins, Silvana
Buzzato e Paulo Sano;
Ao Departamento de Ecologia, pelo apoio e colaboração ao longo do
trajeto;
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Ao pessoal da Seção de Sementes do Instituto de Botânica de São Paulo:
aos profs Nelson Augusto dos Santos Junior e Zé Marcos Barbosa pela
oportunidade que me deram. À Karen, Mônica, seu Antônio, Lamarca, Talita,
Carol, Nestor e Marcio – pessoas queridas que conheci (e que me ajudaram
muito) quando estive por lá!
Ao Pedro Brancalion, pela ajuda com testes de viabilidade;
Aos Srs. João Dagoberto dos Santos e Leandro da ESALQ, e João Paulo
Villani, pelo fornecimento de sementes da juçara;
Aos ajudantes de campo: Cris, Mingau, mãe (!), Vâ, Ju, Isis, Beth e PC;
Ao Maurício Perine, pela incansável ajuda tanto no campo quanto no
laboratório, e ao Wellington Bispo, pelas ajudas computacionais;
Aos que leram e comentaram versões preliminares da Dissertação,
contribuindo muito para a versão final: Ale, Alessandra, Beth e Melina;
Ao Lê Tambosí, pelas altas horas me ensinando geoprocessamento!
Dedico a Figura 1 do capítulo 2 a você!
À minha segunda família: Mingau (claro!), Lu & Gaúcho, Bia & Ceará, JuZ
(Kbeção), Carolzinha, Bira, Nada Mal, Otite (saudades!), Dé, Ogro, Alemão, Lau,
Ka, Jucks, Carol, Cyrus... Por todas nossas conversas, baladas, encontros, viagens
e momentos deliciosamente curtidos, obrigada pela alegria das horas vagas!
Aos amigos não biólogos “das antigas”, às Itaquéias, aos Micaélicos, e em
especial à Anne & German, distantes mas sempre presentes!
Por fim, agradeço também aos que não foram explicitamente citados aqui,
mas que me ajudaram direta ou indiretamente.
E, principalmente, aos futuros leitores, para os quais esse estudo poderá
ser uma fonte de pesquisa!
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Sumário
Resumo Geral 09
Abstract 11
Introdução Geral 13
Objetivos 23
Referências 25
Capítulo 1. Effects of an alien over a native palm tree at the first
demographic stages: subsidies to ecological management 31
Capítulo 2. Comparing the establishment of an invasive and an endemic
palm species in the Atlantic rainforest 53
Discussão Geral e Conclusões 82
Referências 86
Apêndices 88
9
Resumo Geral
A introdução de espécies exóticas, resultando em processos de invasão biológica
em ambientes naturais, é um dos efeitos humanos indiretos que atualmente mais
ameaçam a biodiversidade global. Apesar das invasões biológicas causarem
muitos impactos negativos, elas ainda são pouco estudadas nos ambientes
tropicais megadiversos. A palmeira australiana Archontophoenix cunninghamiana,
inicialmente introduzida para fins ornamentais, tornou‐se invasora de
fragmentos remanescentes de Mata Atlântica no estado de São Paulo. Foi
sugerida como ação de manejo a substituição da A. cunninghamiana pela palmeira
nativa Euterpe edulis. Assim, o objetivo geral deste estudo foi comparar os
estágios demográficos inicias dessas duas espécies de palmeiras, visando
subsidiar a substituição de A. cunninghamiana em fragmentos florestais
invadidos. Realizamos experimentos no interior de um fragmento florestal
urbano (Reserva Florestal do Instituto de Biociências, São Paulo/SP) impactado
pela espécie invasora. No interior do fragmento, analisamos a chuva de sementes
local (por meio de coletores distribuídos acima do solo), a longevidade das
sementes (realizando um experimento de soterramento) e o estabelecimento de
plântulas resultantes de semeadura direta de ambas as espécies. Em laboratório,
testamos os efeitos diretos e indiretos da espécie invasora sobre a germinação de
E. edulis, respectivamente por meio de experimentos de germinação conjunta e
por meio da liberação de substâncias alelopáticas em soluções de lixiviados das
folhas e frutos de A. cunninghamiana. A palmeira invasora não apresentou
nenhum efeito sobre a germinação e formação de plântulas da E. edulis. Mesmo
assim, a palmeira nativa apresentou desempenho inferior nesses estágios, devido
às suas baixas taxas de germinação e de viabilidade resultando em poucas
plântulas formadas, o que evidenciou um gargalo demográfico próprio da
10
espécie. A composição da chuva de sementes indicou uma elevada pressão de
propágulos da palmeira invasora sobre a comunidade nativa, já que mais de 30%
das sementes zoocóricas encontradas pertenciam a A. cunninghamiana. O
experimento de longevidade indicou que ambas as espécies apresentaram bancos
de sementes transientes, o que é vantajoso no controle da espécie exótica, mas
desvantajoso quando se deseja reintroduzir a palmeira nativa por meio de
semeadura. No experimento de semeadura direta, a sobrevivência das plântulas
de ambas as espécies também apontou um desempenho melhor de A.
cunninghamiana. Portanto, nossos resultados demonstraram vantagens da
palmeira invasora nos estágios demográficos inicias quando em co‐ocorrência
com a E. edulis, em condições florestais naturais. Por isso, recomendamos ações
de manejo direcionadas majoritariamente aos indivíduos reprodutivos da A.
cunninghamiana, já que eles produzem elevadas quantidades de sementes, que se
estabelecem rapidamente.
Palavras‐chave: alelopatia; Archontophoenix cunninghamiana; chuva de sementes;
estabelecimento de plântulas; Euterpe edulis; germinação; invasão biológica;
longevidade de sementes; Mata Atlântica.
11
Abstract The introduction of alien species in natural habitats resulting in processes of
biological invasions is one of the indirect human actions which nowadays
threaten global biodiversity. Although bioinvasions usually cause huge negative
impacts in the native biota, they are still little studied in the megadiverse tropical
environments. The Australian palm tree Archontophoenix cunninghamiana, initially
introduced for ornamental purposes, became an invader in remnant patches of
the Atlantic forest, in São Paulo state. The substitution of A. cunninghamiana by
the native palm Euterpe edulis has been proposed as a management action. The
main objective of this study was to compare the first demographic stages of these
two palm species, aiming at subsidizing the substitution of A. cunninghamiana in
invaded forest patches. We performed experiments inside an urban Atlantic
forest patch (Reserva Florestal do Instituto de Biociências, São Paulo/SP)
impacted by the invasive species. Inside the fragment we assessed local seed rain
(through seed traps distributed above soil level), seed longevity (performing a
burying experiment) and seedling establishment (resulting from direct seed
sowing) of both species. At laboratory, we tested both direct and indirect effects
of the invasive species over E. edulis germination through combined experiments
‐ species were put to germinate together ‐ and by testing for the release of
allelopathic substances from A. cunninghamiana leaves and fruits on leachate
solutions. The invasive palm did not show any effect on E. edulis germination
and seedling formation. Even so, the native palm showed lower performance at
these stages, due to low germination and viability rates, and consequently little
seedling formation, evidencing a demographic bottleneck. The seed rain
composition indicated high propagule pressure of the invasive palm over the
forest community, since more than 30% of the zoochorous seeds belonged to A.
12
cunninghamiana. The longevity experiment showed transient seed banks for both
species, what is advantageous for controlling the alien species but not for re‐
introducing the native palm through seed sowing. In the seed sowing
experiment, seedling survival of both species together pointed to a much better
performance of A. cunninghamiana. In conclusion, our results showed advantages
of the invasive palm in the initial phases when co‐occuring with E. edulis in the
forest conditions. We then recommend management actions directed primarily to
A. cunninghamiana reproductive individuals, as they provide high amounts of
seeds that quickly establish.
Keywords: allelopathy; Archontophoenix cunninghamiana; Atlantic forest;
biological invasion; Euterpe edulis; germination; seed longevity; seed rain;
seedling establishment.
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Introdução Geral
Banco de plântulas da palmeira australiana Archontophoenix cunninghamiana no interior da Reserva Florestal do Instituto de Biociências (Universidade de São Paulo, SP). Foto: Ana Luisa Mengardo.
14
As invasões biológicas
As elevadas taxas de extinção, que ocorrem em grande escala nas florestas
tropicais (Turner 1996), colocam esse tema como um tópico central para a
conservação (Chapman & Chapmam 1995; Young, 2000; Kageyama & Gandara
2003). O homem tem papel fundamental nessa atual crise ambiental (Turner
1996), agindo tanto diretamente na destruição de habitats naturais quanto em
formas mais indiretas de perturbação.
A introdução de espécies exóticas é uma destas formas indiretas, e pode
originar processos de invasão biológica, os quais causam impactos negativos em
níveis distintos, como efeitos sobre indivíduos, populações, comunidades,
processos ecossistêmicos e até genéticos (Cronk & Fuller 1995; Williamson 1996;
Mack et al. 2000; Sakai et al. 2001; Traveset & Richardson 2006). Além disso, as
invasões biológicas trazem conseqüências para a vida humana, afetando a saúde,
os sistemas de produção alimentícia e até mesmo os regimes hídricos (Mooney &
Hobbs 2000). Por essas razões, elas têm recebido atenção crescente do ponto de
vista da conservação biológica, sendo consideradas uma das principais ameaças
à biodiversidade em escala mundial (Freitas & Pivello 2005; Perrings et al. 2005).
O processo de invasão biológica pode ser dividido em algumas etapas
(Cronk & Fuller 1995; Mack et al. 2000; Sakai et al. 2001): ele se inicia com a
introdução (acidental ou intencional) da espécie, seguido por sua naturalização,
quando são transpostas as barreiras impostas pelo novo ambiente, relativas à
sobrevivência e à reprodução da espécie (Richardson et al. 2000). Nessa etapa,
pode haver uma facilitação do processo de estabelecimento (devido à ausência de
inimigos naturais no ambiente novo, por exemplo), o que acaba auxiliando no
15
sentido de promover uma eficiente dispersão independentemente da intervenção
humana, dando início a uma invasão bem sucedida (Kowarik 1995a).
Assim, as espécies invasoras são espécies exóticas que se tornaram
naturalizadas e cuja distribuição e/ou abundância está em processo de expansão
(Pysek 1995). É exatamente a habilidade de dispersar rapidamente que
caracteriza as espécies invasoras. Já as espécies apenas naturalizadas formam
populações sustentáveis, mas que não têm a habilidade de dispersão no novo
habitat (Rejmánek et al. 2004).
A primeira teoria sobre as invasões biológicas foi lançada por Darwin, no
final do século 19 (Rejmánek 1996), mas o primeiro livro dedicado ao estudo veio
só no meio do século seguinte, escrito por Elton em 1958 – intitulado “The ecology
of invasions by animals and plants” – podendo ser considerado o início do ramo da
ecologia das invasões (Richardson et al. 2000). Historicamente, a introdução de
espécies além do seu habitat natural começou a se intensificar com a expansão do
colonialismo europeu, quando ocorreram as trocas com o ‘Novo Mundo’ (Cronk
& Fuller 1995). Mas a globalização do século 20 acabou inflacionando esse
processo, criando uma maior homogeneização de espécies e ecossistemas (Mack
et al. 2000; McNeely 2000). Segundo Mooney & Hobbs (2000), as mudanças
globais irão aumentar ainda mais o problema das espécies invasoras nos
próximos anos, já que criarão novos ambientes aos quais as espécies nativas não
estão adaptadas. Isso causará uma queda nas taxas de especiação e perda de
diversidade, resultantes da sobrevivência de espécies invasoras altamente
adaptáveis (Stigall 2010).
Uma das maneiras de se quantificar o impacto ecológico de uma invasão
biológica é a comparação de atributos, já que as espécies invasoras podem
reduzir significativamente a aptidão e o crescimento das nativas, além de
16
modificar a estrutura da comunidade vegetal (Vilà et al. 2011). Dessa maneira,
saber se uma espécie invasora tem maior habilidade competitiva em relação às
espécies nativas co‐ocorrentes também tem consequências importantes para a
conservação (Daehler 2003). Grandes diferenças ecológicas entre uma espécie
invasora e a comunidade nativa onde ela foi inserida (como em relação à
reprodução ou a capacidade de produzir defesas químicas) estão associadas à
maior aptidão da espécie invasora em desenvolver uma explosão populacional
(Strauss et al. 2006).
Várias hipóteses surgiram no sentido de tentar fornecer explicações e
elucidar processos de invasão, baseando‐se em características tanto das espécies
quanto do ambiente invadido (Cronk & Fuller 1995; Heger & Trepl 2003; Alpert
2006), apesar de apenas algumas já terem sido comprovadas empiricamente
(Schaffner et al. 2011). Uma das vertentes nos estudos das invasões biológicas é
direcionada para tentativas em se encontrar características comuns nas espécies
que sejam atributos favorecedores do processo (Sakai et al. 2001; Vilà & Weiner
2004). Por exemplo, Rejmánek (1996) sugere que uma espécie que apresente
frutos carnosos e com oportunidades para a dispersão por vertebrados tem altas
chances de se tornar invasora. Já Hawkes (2007) e Cronk & Fuller (1995)
demonstram que, quando comparadas às espécies nativas do ambiente invadido,
as plantas invasoras são maiores, alocam mais recurso para a reprodução e
também são menos suscetíveis a danos causados por herbivoria. No geral, as
espécies invasoras melhor adaptadas apresentam características de estrategistas
R (p.ex. aquelas dos estágios iniciais da sucessão) mas com certa tolerância ao
sombreamento (característica de espécies sucessionais tardias) e, dessa forma,
podendo também invadir comunidades em estágio sucessional mais avançado
(Cronk & Fuller 1995; Rejmánek et al. 2004).
17
As estratégias de controle ou erradicação de espécies invasoras já
disseminadas são geralmente complexas e custosas. Por isso, antes de se delinear
campanhas de combate à invasão são necessários estudos para se determinar a
priorização de ações e objetivos, visando manter os processos ecológicos naturais
do ambiente (Rejmánek et al. 2004). Há muitas abordagens para a erradicação das
espécies invasoras (Cronk & Fuller 1995), sendo que o controle físico (como o
arranquio das plântulas ou o corte das árvores) é uma das mais comuns.
Entretanto, promover o controle físico de uma espécie pode acabar se revelando
ineficiente se, por exemplo, a espécie apresentar a estratégia de formar banco de
sementes duradouro no solo. Neste caso, o desconhecimento prévio de
características poderá levar o controle ao fracasso. Além disso, o controle de
invasoras que formam stands monoespecíficos pode ser uma forma adicional de
distúrbio na comunidade já impactada pela invasão, pois leva à abertura de
clareiras, interferindo principalmente na regeneração das outras espécies
presentes (Cronk & Fuller 1995).
As invasões biológicas nos trópicos e na Mata Atlântica
Durante algum tempo houve a hipótese de que as invasões biológicas ocorriam
em menor escala nas florestas tropicais por serem essas áreas mais resistentes, já
que apresentam características que naturalmente proporcionariam menores
chances de estabelecimento para uma espécie exótica (Cronk & Fuller 1995;
Londsdale 1999; Mooney & Hobbs 2000; Sakai et al. 2001; Rejmánek et al. 2004).
Há menos invasões reportadas nessa faixa de maior diversidade, com uma média
de apenas 6% de flora exótica nos biomas tropicais mais úmidos, valor menor
que nas regiões temperadas (Lonsdale 1999). Efetivamente, há alguns aspectos da
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floresta tropical podem ajudar a formar uma barreira contra a entrada de
exóticas, como diferenças nas pressões de propágulo das espécies nativas – que
disponibilizam recurso mais homogeneamente ao longo do ano – e a alta
diversidade, tanto funcional quanto de espécies, que promove maior estabilidade
e menor possibilidade de nichos vagos (Londsdale 1999; Fine 2002).
Elton (1958) foi o primeiro a levantar a hipótese de maior resistência das
comunidades mais diversas, mas atualmente sabe‐se que essa “resistência” das
florestas tropicais tem outras explicações menos dependentes de características
intrínsecas do ambiente (Londsdale 1999). As diferenças no número de invasões
biológicas entre áreas tropicais e temperadas podem ser devido a uma questão
de escala de estudo ou ao fato de que poucas espécies tolerantes à sombra já
foram transportadas para os países tropicais (Fine 2002). Ou talvez porque as
invasões nas florestas tropicais são sub‐reportadas (Cronk & Fuller 1995; Fine
2002), o que foi confirmado por Petenon & Pivello (2008), numa revisão sobre o
assunto onde constataram que mais da metade dos estudos em invasões
biológicas excluem os ambientes tropicais. Na América do Sul há casos de
invasão biológica até nas maiores florestas tropicais do mundo, como aquela
causada por insetos drosofilídeos na Amazônia equatoriana, o que demonstra a
suscetibilidade também das florestas tropicais (Acuria et al. 2010).
Outros exemplos de invasões em florestas tropicais mais amplamente
estudados e em maior número de casos estão no Havaí (Fine 2002; Minden et al.
2010), por ser uma ilha com alto endemismo. Também há diversos casos
reportados nas ilhas Maurício (Virah‐Sawmy et al. 2009). Na Mata Atlântica,
onde foi desenvolvido o presente estudo, já foram descritos casos de gramíneas e
samambaias invasoras em áreas mais impactadas (Portela et al. 2009). Fine (2002)
também cita a Musa ornata, uma espécie de bananeira originária da Ásia, que
19
forma densos tapetes no sub‐bosque destas florestas, mesmo em regiões sem
muita interferência humana.
Numa tentativa de mobilização mundial para a conservação da
biodiversidade restante, criaram‐se os chamados hotspots, áreas já bastante
afetadas e diminuídas em seu tamanho original, com alta diversidade de
espécies, associada a grande concentração de endemismos (Myers et al. 2000). A
Mata Atlântica é um desses hotspots mundiais, o que reforça a prioridade em se
desenvolverem projetos de recuperação nos fragmentos remanescentes, visto que
aproximadamente 85% deste bioma já foi eliminado (Ribeiro et al. 2009). Além de
restarem poucas áreas naturais de Mata Atlântica, há previsões para um cenário
ainda pior, com a redução da distribuição de algumas espécies nativas locais de
grande importância, como a palmeira Euterpe edulis (Colombo & Joly 2010).
No estado de São Paulo, grande parte dos remanescentes de Mata Atlântica
estão divididos em pequenos fragmentos isolados (Ribeiro et al. 2009), sujeitos a
uma série de efeitos que podem ter influência sobre as populações e
comunidades ali existentes (Dislich 2002). Quanto mais isolados e menores forem
esses fragmentos, maiores os desafios para sua conservação, uma vez que, nos
fragmentos pequenos, há maior facilidade para perda da biodiversidade (Bruna
1999). Isso ocorre devido, por exemplo, à diminuição no processo de dispersão
por perda da comunidade frugívora (Dislich & Pivello 2002), que diminui o
estabelecimento de novos indivíduos, ou ainda ao aumento dos processos de
perturbação, como as invasões biológicas.
Os fragmentos florestais urbanos e o estudo de caso
20
Em paisagens urbanas, os remanescentes florestais tornam‐se valiosos pelos
serviços ambientais que fornecem e pelo seu papel na proteção da comunidade
nativa (Vidra & Shear 2008). Essas florestas isoladas têm capacidade de amenizar
muitos dos problemas causados pela urbanização, como poluição atmosférica,
impermeabilização do solo e aquecimento climático, além de oferecerem
oportunidades de lazer e de seu valor estético na composição da paisagem
(Dislich 2002).
Os processos ocorrentes não apenas na área invadida, mas também em toda
a paisagem circundante também são importantes para se conservar áreas de
florestas em ambientes urbanos, como, por exemplo, a disseminação e a
plantação de exóticas com fins ornamentais (Vidra & Shear 2008). Em um estudo
realizado em Berlim (Alemanha), 41% do total de espécies existentes na floresta
urbana da cidade eram espécies exóticas, sendo que a urbanização acabou
facilitando e promovendo essa entrada de espécies não‐nativas (Kowarik 1995b).
Isso demonstra que as cidades, particularmente, são muito enriquecidas com
espécies exóticas, e as florestas urbanas geralmente apresentam histórico de
perturbações e, consequentemente, nichos vazios – resultantes da perda de
espécies e da diversidade funcional – e solo nu disponíveis para a entrada de
novas espécies (McNeely 2000).
No presente estudo, discorreremos sobre o processo de invasão biológica
numa reserva florestal urbana de Mata Atlântica (Reserva Florestal do Instituto
de Biociências – RFIB) pela palmeira australiana Archontophoenix cunninghamiana
(Dislich et al. 2002; Dislich & Pivello 2002). Essa espécie foi trazida como
ornamental, a categoria à qual pertencem as árvores invasoras mais bem
sucedidas de florestas tropicais (Fine 2002). A conservação da mata que compõe a
RFIB em seu estado atual não é possível devido ao nível de perturbação em que
21
se encontra, que torna pouco provável a manutenção de um estado de equilíbrio
sem intervenção humana direta (Dislich 2002). Seria necessário realizar um
projeto de restauração visando a uma recuperação em longo‐prazo, que atuasse
na comunidade vegetal e criasse condições de biodiversidade renovável, ou seja,
uma manutenção dos processos naturais sem necessitar intervenções humanas
posteriores. Dessa maneira, o projeto de restauração introduziria espécies
nativas, promovendo uma regeneração artificial, a fim de criar condições para
que as espécies introduzidas fossem, futuramente, auto‐sustentáveis (Kageyama
& Gandara 2003).
Entretanto, um projeto de restauração sem um manejo da espécie invasora
tem grande chance de não ser bem sucedido. Isso porque fatores como alelopatia
e competição podem ser críticos, principalmente nos estágios iniciais de
estabelecimento das espécies nativas introduzidas, contribuindo para a
vantagem competitiva da espécie invasora. Portanto, nesses casos se faz
necessário entender os fatores que determinam o sucesso em cada estágio
demográfico inicial da espécie invasora (germinação – plântula –
estabelecimento), buscando‐se entender como ela se dispersa e persiste, a fim de
identificar estágios mais ou menos críticos para o manejo (McAlpine & Jesson
2008).
As palmeiras e as espécies em estudo
As palmeiras (família Arecaceae) estão entre as fanerógamas mais antigas,
sendo as primeiras monocotiledôneas das quais se tem registro fóssil (Corner
1966; Alves & Demattê 1987). São vistas por muitos como espécies‐chave,
essenciais para a manutenção da diversidade da comunidade, oferecendo
22
recursos valiosos aos frugívoros nas florestas tropicais devido à sua elevada
produção de frutos, que são consumidos por uma grande variedade de fauna
(Terborgh 1986; Galetti & Aleixo 1998; Goulding & Smith 2007). Em fragmentos
florestais de baixa diversidade ou em ambientes pobres em frutos carnosos, os
frutos das palmeiras podem ser ainda mais importantes para os frugívoros do
que em florestas contínuas (Galetti & Aleixo 1998). Apesar de sua importância
ecológica, até pouco tempo atrás pouca atenção era dada a essa família. Mas, na
década de 1980, a WWF (World Wildlife Fund) desenvolveu o primeiro projeto
para conservação das palmeiras da América Latina, o qual tinha como objetivo
principal aumentar o conhecimento sobre o papel das palmeiras como plantas
importantes economicamente (Johnson 1991).
As árvores dessa família são muito conhecidas por características
marcantes, como as folhas grandes, caule solitário e a presença do palmito na
parte terminal do caule. Elas também apresentam crescimento monopodial,
podendo demorar anos para passar de plântula para adulto (Corner 1966). Suas
raízes são fasciculadas, espessas e abundantes, sendo as raízes primárias mais
grossas e fortes dentre todos os vegetais (Corner 1966; Alves & Demattê 1987). Já
a parte reprodutiva é formada por inflorescências que nascem na bainha da axila
foliar e amadurecem após sua queda, fazendo com que as palmeiras floresçam e
frutifiquem continuamente (Alves & Demattê 1987). As palmeiras formam frutos
fibrosos do tipo drupa, com mesocarpo carnoso nas espécies que são dispersas
por animais (Corner 1966; Alves & Demattê 1987); no interior dos frutos, estão
contidas sementes classificadas dentre as maiores nas fanerógamas (Tomlinson
1990).
As duas espécies estudadas – Archontophoenix cunninghamiana H. Wendl. &
Drude e Euterpe edulis Martius – pertencem à sub‐família Arecoideae, que está
23
presente no mundo todo. Na Austrália, há apenas alguns gêneros (como
Archontophoenix), principalmente na região sudeste, enquanto que na América do
Sul há uma flora mais rica e variada dessa sub‐família (Alves & Demattê 1987).
Dentre as diferenças nos gêneros estudados, Euterpe apresenta frutos curvos e
estigmas laterais, além de endosperma não‐ruminado nas sementes, o que é
considerada uma forma mais primitiva; já o gênero Archontophoenix tem frutos
retos e estigma terminal, com sementes laterais que possuem endosperma
ruminado, o que permite maior dispersão do oxigênio na semente, por
proporcionar uma maior área de contato entre o endosperma e o tegumento
(Corner 1966; Alves & Demattê 1987).
OBJETIVOS
O presente estudo teve como objetivo geral comparar o estabelecimento inicial de
duas espécies de palmeiras, visando um manejo por substituição da espécie
invasora, Archontophoenix cunninghamiana, pela nativa, Euterpe edulis, em
fragmentos florestais de Mata Atlântica.
Como objetivos específicos, temos:
1. comparar a germinação e o desenvolvimento de plântulas das duas
espécies em condições naturais simuladas;
2. verificar a possível liberação de substâncias alelopáticas pela palmeira
invasora, o que poderia inibir ou impedir a germinação ou o
desenvolvimento da palmeira nativa no ambiente florestal;
24
3. determinar a viabilidade e a longevidade das sementes das duas espécies
armazenadas no solo da floresta, a fim de estimar o potencial de
regeneração de ambas as espécies no fragmento invadido;
4. avaliar a contribuição da A. cunninghamiana na chuva de sementes do
fragmento florestal urbano, a fim de estimar a atual pressão de propágulo
ao qual está submetido;
5. comparar o estabelecimento de plântulas das duas espécies após
semeadura direta no solo da floresta.
A dissertação divide‐se em dois capítulos, apresentados sob o formato de
manuscrito nos moldes das revistas para as quais foram submetidos. O capítulo
1, submetido para o periódico Plant Species Biology, trata da parte de
experimentos em laboratório, abrangendo os objetivos específicos 1 e 2, acima
citados. O capítulo 2, submetido para o periódico Plant Ecology and Diversity,
enfoca os três últimos objetivos específicos acima citados, com ênfase no trabalho
de campo. Na sequência há uma discussão geral e as conclusões do estudo,
abordando os principais aspectos levantados nos dois capítulos. No final da
dissertação apresenta‐se o apêndice, que não foi incluído na submissão dos
manuscritos, mas que foi aqui inserido para a visualização de alguns aspectos
citados ao longo dos capítulos.
25
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Capítulo 1
Effects of an alien over a native palm tree at the first demographic stages:
subsidies to ecological management
(Efeitos de uma palmeira exótica sobre uma nativa nos estágios demográficos
iniciais: subsídios ao manejo ecológico)
Mengardo, A.L.T. & Pivello, V.R. Manuscrito original submetido ao periódico
“Plant Species Biology”.
Experimento de germinação conjunta da Archontophoenix cunninghamiana com Euterpe edulis indicando formação de plântulas de ambas as espécies. Foto: Ana Luisa Mengardo.
32
ABSTRACT
Biological invasions usually bring negative impacts to native biota, being
included among the major causes of biodiversity loss. The Australian palm tree
Archontophoenix cunninghamiana became invasive in patches of the Atlantic forest,
and the native endemic palm Euterpe edulis is threatened to extinction in many of
these same patches. Both species would occupy parts of the same functional
niche in forest remnants, and therefore, the substitution of A. cunninghamiana by
E. edulis is recommended. Our hypothesis for the great success of A.
cunninghamiana presumed it had high germination and viability rates, and
allelopathic properties that could influence the recruitment of the native palm
species. We compared the initial demographic stages of these two palms. To infer
about germination efficiency we tested both direct effects, through combined
germination experiments, and indirect effects (allelopathy) of A. cunninghamiana
on E. edulis by adding aqueous leachate solutions of A. cunninghamiana fruits and
leaves to E. edulis seeds. The leachate solutions neither inhibited germination nor
affected the length of E. edulis seedlings. In the combined germination tests, A.
cunninghamiana was significantly affected when seeds were not depulped;
however, germination rates were high for depulped seeds. Euterpe edulis showed
high mortality in the initial demographic phases. Therefore, actions to both
eliminate A. cunninghamiana and reintroduce E. edulis are necessary to restore the
native biodiversity since E. edulis would not be able to self‐reestablish in invaded
forest patches. Therefore, management measures can be taken with no need to
concern about the release of allelochemicals by A. cunninghamiana.
Keywords: allelopathy, Archontophoenix cunninghamiana, Arecaceae, Euterpe
edulis, germination
33
Introduction
The rapid vanishing of tropical forests around the world is being caused
both by direct or indirect human actions (Turner 1996), and biological invasions
would fit as one of the most harmful disturbance factors indirectly derived from
species introductions by man. When introductions results in biological invasion
processes, negative impacts can be observed at distinct levels: individuals,
population and community dynamics, ecosystem processes, and even at genetic
level (Cronk & Fuller 1995; Pysek et al. 1995; Rejmánek 1995; Williamson 1996;
Vitousek et al. 1997). For this reason, biological invasions have received
increasing attention from biological conservationists (Pysek 1995), being
considered one of the major threats to biodiversity at global scale (Cronk & Fuller
1995; Vitousek et al. 1997; Perrings et al. 2005; Petenon & Pivello 2008).
Understanding the causes behind invasions is a difficult task, as well as
the reasons why species successfully establish and spread in new habitats.
Callaway and Aschehoug (2000) argued that many invasive species are not
dominant competitors in their natural habitats, however, they can successfully
eradicate their new neighbors such as by releasing phytotoxins which inhibit or
eliminate the surrounding organisms. This allelopathic action was proposed as
an alternative theory to explain the reason why invaders become more abundant
and competitively dominant in invaded sites, acting as a modeling mechanism of
the process (Callaway & Aschehoug 2000; Inderjit et al. 2008).
The palm tree Archontophoenix cunninghamiana H. Wendl. & Drude
(Arecaceae), native to the tropical Australian forests, was introduced in Brazil for
ornamental purposes by the years of 1960. However, its establishment in urban
areas resulted in biological invasion processes on remnant Atlantic forest patches
nearby, especially in the southeastern part of the country (Dislich et al. 2002;
34
Dislich & Pivello 2002). In São Paulo city, this palm species showed a growth rate
of 19.4% per year (individuals with diameter at breast high ≥ 9.5cm) in an urban
forest patch, value rarely found amongst arboreal species of tropical forests
(Dislich et al. 2002). Besides, the species represented 22.5% of all adult individuals
in the same patch, the highest density of more than a hundred native arboreal
species registered in the area (Dislich et al. 2002).
On the other side, the palm tree Euterpe edulis Martius (Arecaceae) is
native and endemic to the Atlantic rainforest (Henderson & Galeano 1996).
Despite being in the past one of the species with the highest densities and
frequencies in dense ombrophylous forests (Queiroz 2000; Reis et al. 2000) it is
now extinct in many regions (Galetti & Fernandez 1998), and large populations
of E. edulis are only found in few protected reserves (Galetti & Aleixo 1998),
being barely found in small forest patches (Reis et al. 2000).
One of the factors that probably contribute to the invasion success of the
exotic palm A. cunninghamiana in remnant Atlantic forest patches is, among
others, its continuous fruit production around the year (Mengardo, A.L.T. and
Pivello, V.R., unpublished data). This alien species probably overlaps parts of the
niche previously occupied by the native E. edulis (Dislich, 2002), as the latter was
one of the few species to provide nutritional fruits to the frugivorous fauna in the
winter (Galetti & Aleixo 1998; Silva Matos and Watkinson 1998; Mantovani &
Morellato 2000). The replacement of A. cunninghamiana by E. edulis would restore
the threatened native palm species to its habitat, and also would provide a more
nutritious food resource to frugivores (Mengardo, A.L.T. and Pivello, V.R.,
unpublished data), and therefore, it has been recommended as a management
action in the invaded Atlantic forests patches (Dislich 2002; Christianini 2006).
35
The cutting of all A. cunninghamiana individuals in an invaded forest patch
would be very laborious and costly, as these individuals may reach about 20 m
high, and the Atlantic forest relief is characteristically hilly, making difficult the
access to individuals and the removing of the cut trees. Another alternative
would then be the sowing of E. edulis in the invaded fragments, either manually
or through overflight. In this case, to assure a successful establishment of the
native species it is vital to know if the invasive species is able to interfere in its
early demographical stages otherwise the reintroduction could be jeopardized,
and efforts and money would be spent without the expected results. To achieve a
well‐succeeded reintroduction, the native species must also have conditions to
recruit new individuals and to obtain some competitive advantage over the alien
that will continue to disperse fruits throughout the forest.
Among the challenges of the recruitment process of palms, the
germination phase, seed viability and growth are primordial, therefore, the
establishment phase brings a high cost to the species (Mullett et al. 1981).
However, these initial demographic stages are vital to maintain the population,
since the highest mortality rates occur in the seedling establishment phase at soil
level (Herrera et al. 1994; Castro et al. 2004).
Facing this panorama, the aim of this study was to evaluate the viability of
sowing the native palm species Euterpe edulis in Atlantic forest patches invaded
by A. cunninghamiana in order to restore E. edulis populations and control the
bioinvasion process. Considering the existence of a seed bank of A.
cunninghamiana in the invaded patch, we compared the first demographic stages
(germination, seedling development) of both species simulating natural
conditions. We also verified the possible release of allelopathic substances by the
exotic palm species on the forest floor, which could inhibit E. edulis germination
36
and/or development. Our main hypotheses were i) the seeds of A.
cunninghamiana have higher viability and germination rates than those of E.
edulis, and consequently, this native species would have disadvantage in the
establishment phase, and ii) the fruits and dry leaves of A. cunninghamiana
release allelopathic substances on the forest floor that may inhibit the
germination of E. edulis, and thus reduce its chances of establishment.
Materials and Methods
Study Species
Archontophoenix cunninghamiana H. Wendl. & Drude (Arecaceae) is a
solitary palm tree with green pinnate leaves, and pending inflorescences
(bunches) at the trunk under the leaves (Lorenzi et al. 2004). In the southeast of
Brazil, it shows a generalized dispersal system (Howe 1993) producing rounded
red drupes abundantly along the entire year, with a small amount of nutrients in
the pulp and a big fibrous hard lump (Mengardo, A.L.T. and Pivello, V.R.,
unpublished data). The species shows a rapid growth at full sun or half shadow,
adapting well to the subtropical conditions of that part of Brazil (Lorenzi et al.
2004).
Euterpe edulis Martius (Arecaceae) is native to the Atlantic rainforest,
originally occurring at the east and southeast of Brazil. Its palm heart is very
appreciated as food, and because of that it has been severely exploited, leading to
current extinction in most of its original area (Galetti & Aleixo 1998; Galetti &
Fernandez 1998). Its fruits are spherical drupes with a thin epicarp, purple or
black when mature, and a fibrous mesocarp (Henderson & Galeano 1996), being
available from December to September (Silva Matos & Watkinson 1998). This
species is used as a food delicacy (palm heart and pulp), in rural building (trunk)
37
or even as ornamental (Lorenzi et al. 2004). In this case, the palm can be planted
in urban areas as an alternative to A. cunninghamiana, serving not only as an
aesthetic element but also as a food source to local avifauna, due to the high
nutritional content of its fruits (Mengardo, A.L.T. and Pivello, V.R., unpublished
data). Euterpe edulis contributes to the maintenance and restoration of forest
remnants (Reis et al. 2000) and it is considered a keystone species to frugivorous
fauna (Galetti and Aleixo 1998; Silva Matos & Watkinson 1998). The decline in
some Atlantic forest avian populations has been attributed to the devastation of
this native palm (Galetti & Aleixo 1998).
Sampling and processing
We used stones (hereafter generically called seeds, although the endocarp
attached to the seed is also included) removed from intact mature fruits from
both species, collected in December 2009. The fruits of A. cunninghamiana were
collected from ornamental matrices at the Universidade de São Paulo, in São
Paulo city (23o33’57”S and 46o43’43”W). Euterpe edulis fruits were collected from
randomly selected natural matrices at the Neblinas Park, in Mogi das Cruzes city
(23o44’07”S and 46o11’05”W). Fruits were processed and depulped right after
collection, since the seeds of both palms do not show dormancy nor tolerate
desiccation (Corner 1966). Fruits were soaked in water at room temperature for
24 hours to facilitate the removal of the mesocarp (Meerow 2004). Afterwards,
the pulp was mechanically removed and dried in the shade (Brasil 1992a;
Meerow 2004).
Seed viability
38
Seed viability tests were carried out before and after the germination
experiments. Before the experiments, a random selection of 100 seeds of both A.
cunninghamiana and E. edulis were tested to determine the species mean viability.
After the germination experiments, viability tests were performed on the
remaining ungerminated and intact seeds of each replicate.
Seed viability tests were carried out by opening the seeds longitudinally
and exposing the embryo (see Appendix I). These seeds were soaked in
Tetrazolium salt solution (2,3,5 triphenyl chloride) at 0.5%, in the dark during 5
hours at 30ºC (test for E. edulis according to Brasil 1992b; ISTA 1993). Seed
viability was visually determined, and seeds which showed light reddish color in
more than 50% of the embryo were considered viable (Biagioni & Godoy 2005).
The ones physically deformed, with uncolored or intensely red‐colored embryo
were considered not viable (França‐Neto et al. 1998; Ferreira et al. 2007) (see
Appendix I).
Interference experiments
We conducted experiments to assess both direct and indirect (allelopathy)
effects of the invasive palm species on the germination of the native palm.
Experiments to test direct effects were conducted using both palm species
(A. cunninghamiana and E. edulis), and simulating field conditions. Three
treatments were established: i) germination of each species separately (control);
ii) germination of both species together using only seeds (depulped fruits); iii)
germination of both species together using E. edulis seeds and A. cunninghamiana
recently collected fruits (seed + pulp). All tests followed a randomized design of
nine replications with 12 seeds, or fruits, per treatment. Germination was carried
39
out in a greenhouse (25ºC ± 2ºC, air relative humidity = 80%), and observed
during 20 weeks, until no more seeds germinated after 15 consecutive days.
Seeds were considered germinated when coleoptiles were visible.
Germinated seeds were left in the germination box until their primary leaves
emerged (see Appendix I). Seedlings length was then measured.
We considered the following variables: 1) germination percentage; 2)
germination velocity index (GVI, number of days taken to germinate, according
to Borghetti & Ferreira 2004); 3) length of seedling.
We also tried to represent the natural forest conditions to assess the
indirect effects (allelopathy) of A. cunninghamiana over E. edulis seed germination,
by using aqueous leachate solutions of A. cunninghamiana fruits and leaves,
instead of making extracts with crushed material. Allelopathy was tested because
there is a natural massive fall of A. cunninghamiana leaves and fruits in the forest
floor, and they are constantly washed out by rainfall. In the invaded forest patch,
we observed the volumes of fruits and leaves at the forest floor next to the base
of A. cunninghamiana individuals to produce ecologically relevant concentrations
(as in Dietz et al. 1996). Recently collected fruits were used in the proportion of 80
g to 120 ml of distilled water, generating the highest concentration solution of
approximately 66%. Two other solutions were prepared from the dilution of that
one, at approximately 33% and 16.5%. Aqueous solutions of dry leaves leachates
were obtained from 45 g of leaves in 400 ml of distilled water, resulting in the
highest concentration of 11% and subsequent dilutions of 5.5% and 2.75%. The
solutions were filtered and stored at 8ºC.
In order to test for allelopathic effects, we established three treatments for
E. edulis seed germination: i) irrigated with water (control); ii) irrigated with fruit
40
leachate solution at the concentrations of 66%, 33% and 16.5%; and iii) irrigated
with dry leaf leachate solution at the concentrations of 11%, 5.5% and 2.75%.
Statistical analyses
In the germination experiments we applied one‐way ANOVA followed by
Tukey’s test for all measured variables, or Kruskal‐Wallis analysis followed by
Dunnett’s a posteriori test when the assumptions of normal distribution and
homogeneity were not met. To verify differences among species in these same
experiments we applied the simple t test, or Mann‐Whitney to non normal
residuals distributions, for each treatment independently. In the tests for
allelopathic effects we used a two‐factorial ANOVA to assess differences among
treatments according to the factors (fruit/leaf solution and different
concentrations), followed by Tukey’s a posteriori test.
Results
Our results showed no effects of A. cunninghamiana leachate solutions on
E. edulis germination rates (df=8; F=0.902; p=0.52) or germination velocity (df=8;
F=0.4214; p=0.66), concerning both different parts of the plant and different
concentrations of solutions (Figures 1A and 1B). Average seed germination rate
of E. edulis was 40.74% in all treatments, including the control (Figure 1A),
despite the initial viability test indicated 73.10% of seeds available to germinate.
All E. edulis seeds classified as non‐germinated at the end of the experiment and
submitted to the viability test were not viable. Moreover, A. cunninghamiana
leachate solutions did not affect E. edulis seedling length (df=8; F=1.047; p=0.41),
which maintained in average 14.43 cm (±1.55) from the top of coleoptile to the
end of primary root (Figure 1C).
41
Germination treatments with seeds of both species together showed no
effect of A. cunninghamiana on of E. edulis germination (p>0.05, Figure 2A). On the
other hand, the seeds of A cunninghamiana showed a significant reduction in
germination rate in the treatment using the whole fruit (H=18.04; p<0.001, Figure
2A). After the end of the experiment using fruits, 30.56% of A. cunninghamiana
seeds were still viable, against none of E. edulis.
In general, E. edulis seeds showed lower germination rates compared to A.
cunninghamiana in the control (df=2; t=11.98; p<0.0001) and in the treatment with
seeds of both species together (df=2; t=‐3.55; p=0.003). Germination rate of E.
edulis was in average 43.52% (the initial seed viability was 73.10%), against
88.43% of A. cunninghamiana (initial seed viability was 84.80%). On the other
hand, E. edulis seeds showed higher germination rates compared to A.
cunninghamiana (51.85% and 20.37%, respectively) in the treatment using the
fruits (seeds + pulp) (df=2; t=‐3.54; p<0.01, Figure 2A).
No differences could be found in germination velocity among treatments
concerning E. edulis (F=0.902; p=0.52), but A. cunninghamiana revealed a different
pattern: the germination velocity index decreased from 2.41 in the control
treatment to 0.98 in the treatment with both species seeds, and to only 0.059
when using A. cunninghamiana fruits (F=375.82; p<0.001, Figure 2B). Therefore,
the exotic species ended up germinating faster than E. edulis in the control
treatment (t=7.59; p<0.0001), at similar velocity when both seeds were together
(t=1.045; p=0.31), and slower when fruits were used (t=‐8.02; p<0.0001, Figure 2B).
Seedlings of E. edulis were in average 15 cm (±1.52) long, while A.
cunninghamiana had smaller seedlings (t= ‐4.94; p<0.001) of ca. 11 cm (±0.73) both
in the control (Figure 2C) and in the treatment with both species seeds. However,
a significant decrease in A. cunninghamiana seedlings length occurred in the
42
treatment using fruits, in average 5.6 cm (±5.30) (df=2; H=15.95; p<0.001, Figure
2C).
Discussion
Our hypothesis that A. cunninghamiana would have allelopathic effects
over E. edulis germination was rejected, as we could not verify any allelopathic
effect on E. edulis germination rates and velocity, and neither on its seedlings
length. We also conducted the same tests with Lactuca sativa L. cv. Grand Rapids
(Asteraceae) and Lycopersicon esculentum Mill. (Solanaceae) – standard species
used in tests of germination and allelopathy due to their responsiveness and
rapid germination (Ferreira & Aquila 2000) – and another native species,
Pterogyne nitens Tul. (Fabaceae), and none of them showed to be affected by the
leachate solutions of A. cunninghamiana (Mengardo, A.L.T, unpublished data).
Allelopathic substances are not commonly described in palms, but Arecaceae
species usually show mechanical structures and ergastic substances (e.g. tannin
and silica) as defense strategy (Tomlinson 1990). Additionally, the wax of leaves
may also be a barrier to harmful soluble substances (Alves & Demattê 1987).
Our second hypothesis presumed higher germination and viability rates
of A. cunninghamiana compared to E. edulis that would inhibit the native species
recruitment. This hypothesis was confirmed, as viability rates of E. edulis and A.
cunninghamiana were, respectively, 73.10% and 88.43%.
In the germination tests with both species together we expected negative
interactions from A. cunninghamiana on E. edulis, but curiously, A.
cunninghamiana was the one to show low germination rates and velocity in tests
where the whole fruits were used. That was probably due to the barrier effect
created by the pulp, which delayed water absorption by seeds. According to
43
Corner (1966), pulp tissue may inhibit or delay germination, and seeds only
begin to germinate when the pulp starts to decompose and parts of the endocarp
are exposed. Such germination delay can trigger other consequences, as lower
seedling length compared to depulped seeds. In this sense, the lower
germination rates and velocity may not be related to the treatment applied.
Comparing the species germination rates, E. edulis showed less than half
the value of A. cunninghamiana (44% against almost 90%), and germination
velocity was significantly slower. Therefore, the rapid and effective spread of A.
cunninghamiana individuals throughout the forest may be related to its high
germination rates, and consequently higher chance of successful establishment.
In the germination experiments performed, A. cunninghamiana viability rates
were higher than those predicted by the initial tests, since approximately 85% of
viable seeds resulted in about 90% of germinated seeds. A similar pattern was
maintained in the germination experiments using seeds (depulped fruits).
The low germination rates here observed for E. edulis seeds have already
been reported by other authors. Some studies registered a germination rate of
around 55% under controlled conditions (Bovi & Cardoso 1975; Silva‐Matos &
Watkinson 1998). However, germination rates in the field decreased to only 26%
(Reis & Kageyama 2000). Tavares et al. (2008) also found low germination rates
and high mortality in seeds of E. edulis, and this can be attributed to the species
non‐domestication, consequently without artificial selection (Nodari & Fantini,
2000). On the other hand, A. cunninghamiana has been used for ornamental
purposes and has probably gone through artificial selection towards vigorous
individuals that could produce vigorous offspring.
Reis et al. (2000) discussed the pyramid‐shaped demography of E. edulis in
natural habitats, with a massive production of seeds and progressively much
44
smaller proportions of viable seeds in the soil, of seedlings, juveniles and adults,
respectively. This structure narrows the species bottleneck at the first
demographic stages, since only about 5% of total fruit production turns out to be
viable seeds in the soil seed bank, and less than 3% become seedlings (Nodari et
al. 2000). Despite that, planting the fruits or seeds of E. edulis is still an effective
way of reintroducing the species in degraded areas (Queiroz 2000), even though
the success is limited by variations in local moisture and shadow during the
germination phase (Tavares et al. 2008). Therefore, besides the reintroduction of
E. edulis in the Atlantic forest patches invaded by A. cunninghamiana, other
actions are necessary to decrease the exotics seedling establishment in order to
enhance the chances for E. edulis regeneration, since the exotic palm showed
better performance at the initial phases of life.
According to the enemy release hypothesis, invasive species are also
favored by the lack of specialist pathogens and herbivorous during the
recruitment phase (Keane & Crawley 2002). The absence of these regulators can
play a crucial role (Inderjit et al. 2008) since the invasives show low seed
mortality and they can, therefore, leave more descendants and be more effective
concerning the reproductive process. Reis and Kageyama (2000) detected high
mortality in seeds of E. edulis found over the soil – up to 55% of all non‐
germinated seeds – due to the action of microorganisms or predators. Nodari et
al. (2000) carried out an experiment of E. edulis seed sowing in a secondary forest
which resulted on the survival of only 38% of total seeds after 12 months. It thus
seems that E. edulis faces much greater challenges to establish in the forest
compared to A. cunninghamiana.
A barrier to the good performance of A. cunninghamiana in the initial life
stages can be the germination from its fruits. Low germination rates in the
45
experiments using the whole fruits indicate the importance of the frugivorous
community to that species success, since not removing the pulp may inhibit or
delay germination.
In conclusion, in the management of an area invaded by A.
cunninghamiana measures can be taken with no concern about the release of
allelochemicals by its leaves or fruits.
Also, the reestablishment of E. edulis populations in invaded forest
patches of the Atlantic forest will be hard if it depends only on the recruitment
by seeds. Nevertheless, this difficulty shall not be attributed to any effect of the
invasive over the native, but mainly to the natural bottleneck that E. edulis shows
at this early demographic stages.
Acknowledgments
The authors specially thank Profs. Drs. Alessandra Fidelis, Paulo Takeo
Sano and Silvana Buzzato for valuable suggestions in the manuscript. We also
thank. Prof. Dr. Nelson Augusto dos Santos Júnior and people from the Seeds
Section of the Instituto de Botânica de São Paulo for the support in the
laboratory, and Prof. Dr. Sergio Tadeu Meirelles and Maurício Perine for field
and laboratory assistance. This study was supported by FAPESP (Fundação de
Amparo à Pesquisa do Estado de São Paulo, 2008/56015‐8).
46
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Figure 1. Germination rate (A), germination velocity index ‐ GVI (B) and seedling length (C) of E. edulis in tests for A.
cunninghamiana allelopathic effects (Mean ± SE, p≥0.05). Control was watered with distilled water; leachate solutions of A.
cunninghamiana dry leaves at concentrations of 11% (high), 5.5% (medium) and 2.75% (low); leachate solutions of A.
cunninghamiana fruits at concentrations of 66% (high), 33% (medium) and 16.5% (low).
Control Leaves Fruits30
40
50
60
Ger
min
atio
n (%
)
Control Leaves Fruits0.9
1.2
1.5
1.8
GV
I
Control Leaves Fruits13
14
15
16
See
dlin
g le
ngth
(cm
)
distilled water high medium low
ns nsns
Figure 2. Germination rates (A), germination velocity index ‐ GVI (B) and seedling length (C) of E. edulis and A.
cunninghamiana at combined germination experiments (Mean ± SE); Different letters indicate significant differences
(p≤0.05); C=control (independent germination); Gs= seed germination of both species together; Gf= germination of both
species together using seeds of E. edulis and fruits of A. cunninghamiana.
C Gs Gf
25
50
75
100
Ger
min
atio
n (%
)
C Gs Gf0.0
0.8
1.6
2.4
GVI
C Gs Gf
4
8
12
16
Seed
ling
leng
th (c
m)
A. cunninghamiana E. edulis
a
aa
aa
b
b
b
bb
bb
b
c
c
c
b
b
(a) (c)(b)
Capítulo 2
Comparing the establishment of an invasive and an endemic palm species in the
Atlantic rainforest
(Comparando o estabelecimento de uma espécie de palmeira invasora e uma
endêmica na Mata Atlântica)
Mengardo, A.L.T., Figueiredo, C.L. & Pivello, V.R. Manuscrito original
submetido ao periódico “Plant Ecology and Diversity”.
Plântulas da Archontophoenix cunninghamiana (direita) e da Euterpe edulis (esquerda) em co-existência, durante o experimento de semeadura direta, na Reserva Florestal do Instituto de Biociências (Universidade de São Paulo).
Foto: Ana Luisa Mengardo.
54
Abstract
Background: Despite figuring among the major causes of biodiversity loss,
bioinvasions are still little studied in tropical environments, and researches on
invasion ecology are necessary to support management actions on negatively
impacted habitats. The Australian palm tree Archontophoenix cunninghamiana was
initially introduced in Brazil for ornamental purposes but became an invasive
species in urban and suburban forest patches; today it represents a threat to the
Atlantic rainforest biodiversity. The substitution of A. cunninghamiana by the
native palm Euterpe edulis has been proposed.
Aims: Compare the regeneration potential of these two palm species in an
invaded Atlantic forest patch. We focused on the contribution of A.
cunninghamiana to the local seed rain and seed bank, and we compared seedling
establishment of both species.
Results: From the 42,836 diaspores collected in the seed rain (12 months), 1015
(2.3%) belonged to A. cunninghamiana in a density of 6.77 seeds m‐2 year‐1, what
represents a high propagule pressure in the community. Both species did not
showed persistent seed banks, what is suitable for the exotic species control but
brings an additional challenge for keeping the native palm tree in the
community. Seedling survival experiments pointed to a much better
performance of A. cunninghamiana with 30.3% survival rate against only 3.5% of
E. edulis.
Conclusion: We recommended management strategies directed primarily to the
reproductive individuals of A. cunninghamiana as well as periodical sowing of E.
edulis or the transplant of juveniles.
Keywords: Archontophoenix cunninghamiana; biological invasion; Euterpe edulis;
seedling establishment; seed longevity; seed rain.
55
Introduction
Biological invasions figure among the major causes of biodiversity loss
(Cronk and Fuller 1995; Vitousek et al. 1997; Perrings et al. 2005), and have long
interested the scientific community, who try to understand their causes, and also
to create and test techniques to control or eradicate the invasive species. Several
hypotheses have already been presented, which tried to find out the attributes of
a species that makes it invasive, or the typical features of the more easily invaded
environments (Rejmánek 1996; Alpert 2006).
Bioinvasions are little studied in tropical forests, although they can lead to
severe changes in vegetation structure, forest self‐maintenance and regeneration
(Fine 2002; Petenon and Pivello 2008; Vilà et al. 2011). Among the world tropical
forests, the Atlantic rainforest is considered a biodiversity hotspot (Myers et al.
2000) and is severely threatened since around 85% of its original area has been
converted into other land uses (Ribeiro et al. 2009). Therefore, the conservation of
the remaining Atlantic rainforest areas is of a great urgency, especially those
which are threatened by biological invasions and deforestation.
Studies on bioinvasion ecology are necessary to support the design of
management actions in the impacted habitats (Ferrera and Galetto 2010). One of
the approaches to investigate the invasion process is to evaluate species
recruitment potential, what helps to make predictions about their future
expansion and to elaborate effective management plans (McAlpine and Jesson
2008). The process of plant recruitment starts on the species dispersal and ends
on the seedling establishment, and all stages between these two phases are
critical for the perpetuation and persistence of most species (Herrera et al. 1994;
Gurevitch et al. 2002; Castro et al. 2004). The phase of seedling establishment also
56
figures among the major causes of a species absence or rarity in the community
(Clark et al. 1999).
Seed dispersal effectiveness can be measured in terms of quantity and
quality, and the latter parameter is divided on movement and deposition
patterns (Schupp 1993). Therefore, the availability of propagules depends on the
species ability to disperse both in space (seed rain) and time (seed bank). These
two parameters – the species representativeness in the seed rain and its seed
bank longevity – can determine the success of invasive species in the plant
community, and are crucial for the management effectiveness aiming at
ecosystem restoration (Bakker et al. 1996; Panetta 2004; Cutway and Ehrenfeld
2010). Moreover, the invasive potential in the long‐term can be determined by
the invasive propagule pressure (fecundity and dispersal) against the resistance
of the native community (Martin and Canham 2010).
The zoochoric palm tree Archontophoenix cunninghamiana H. Wendl. &
Drude is original from tropical Australia and was initially introduced in Brazil
for ornamental purposes. The species has dispersed from urban gardens to
surrounding remnant forest patches, and today represents a threat to the Atlantic
rainforest biodiversity (Dislich et al. 2002; Dislich and Pivello 2002). Studies
conducted in a patch invaded by this alien palm showed a growth rate rarely
found amongst arboreal species of tropical forests (Silva Matos and Pivello 2009).
The substitution of A. cunninghamiana by a native palm species has been
proposed as a management action focusing on the frugivores that already use the
exotic palm as food resource. Since the alien palm is prolific and shows an
asynchronous fruit production all year round in the invaded forest fragments
(Mengardo and Pivello 2007), the substitute native species should be able to
57
provide fruits in the scarcity period of winter, as presently does A.
cunninghamiana.
Euterpe edulis Martius is pointed as a potential substitute for the invasive
Australian palm (Dislich 2002; Christianini 2006). E. edulis is native and endemic
to the Atlantic rainforest (Henderson and Galeano 1996), and constitutes an
important food resource to the frugivorous community, especially during the
winter (Galetti and Aleixo 1998; Mantovani and Morellato 2000). Still, the
nutritional content of E. edulis fruits is superior to that of A. cunninghamiana
(Mengardo and Pivello 2007). Moreover, although E. edulis was once one of the
most frequent species in the southeastern Atlantic rainforest (Queiroz 2000; Reis
et al. 2000) it is nowadays locally extinct in many regions due to overexploitation
and deforestation (Galetti and Fernandez 1998). Large populations of E. edulis are
only found in protected reserves (Galetti and Aleixo 1998), being barely found in
the smaller patches (Reis et al. 2000).
A promising way of reintroducing E. edulis in forest patches is by sowing
its depulped fruits (seeds) (Queiroz 2000), an easier and cheaper way compared
to planting a large number of juveniles. However, before performing such
management in the invaded patches it is crucial to test possible interferences –
e.g. competition – of the alien species in the first demographic stages of E. edulis,
as it is usually caused by invasive species (Vilà and Weiner 2004). Otherwise, all
the effort and money employed in the reintroduction process could be wasted.
Moreover, comparisons between the native and the alien species can address the
question of what attributes enhance the spreading of the alien over the native
(van Kleunen et al. 2010).
This study intended to assess the regeneration potential of those two palm
species in an invaded patch of the Atlantic forest by analyzing the seed rain, and
58
comparing seed viability, longevity and establishment of A. cunninghamiana and
E. edulis. The main questions we aimed to answer were: i) how important is the
contribution of the invasive palm tree in the local seed rain?; ii) does the invasive
species keep a longer‐lasting seed bank compared to the native species?; iii) are
there differences on seedling survival between the invasive and the native palms,
and if so, will such differences interfere in the species establishment? iv) is the
sowing of E. edulis seeds a good strategy to successfully reintroduce this species
in the invaded Atlantic forest patch?
Material and methods
Study area
The study was carried out in the forest reserve of the Universidade de São
Paulo, in São Paulo city, SP, Brazil. The 10.21 ha fragment (Rossi 1994) is located
inside the university campus (23º33’44”S and 46º43’49”W, 735‐765 m a.s.l., Figure
1). The soil is clayey and acid, nutrient poor and aluminum rich in some sites
(Varanda 1977). Local climate is humid subtropical (Cwa, Köppen 1948), with
mean annual temperatures around 19.2oC, mean air humidity around 80%, and
annual precipitation near 1200 mm (Joly 1950; Varanda 1977; Rossi 1994). The
local original vegetation belonged to the dense ombrophylous forest dominium
(Veloso et al. 1991), a predominant physiognomy of the Atlantic rainforest.
The study site was assigned as natural preserve in 1973, becoming one of
the few protected urban areas of the southern Atlantic forest (Dislich 2002). It
represents a mosaic of different degradation and regeneration stages (Rossi
1994), and comprises ca. 103 native woody species (Dislich 2002), which is a
relatively low number for that forest type (Rossi 1994), possibly due to the
negative impact of A. cunninghamiana invasion. A. cunninghamiana was planted in
59
the neighboring gardens about 50‐60 years ago, and today is the most abundant
tree species inside the reserve (Dislich et al. 2002).
Studied species
Archontophoenix cunninghamiana H. Wendl. & Drude (Arecaceae) is a
solitary Australian palm tree with pinnate leaves and pending inflorescences
(bunches). It is a prolific species, producing more than 3600 fruits per bunch
throughout the entire year, dispersed mainly by generalist birds (Christianini
2006; Mengardo and Pivello 2007). Fruits are small red drupes, the pulp is
nutrient poor and most of the fruit mass is a fibrous hard lump (Mengardo and
Pivello 2007). Considering the Arecaceae family, this species shows a rapid
growth at full sun or half shadow, adapting well to the subtropical conditions of
Southeast Brazil (Lorenzi et al. 2004). In our study site, previous researches
showed growth rates of 6.31% year‐1 and 8.63% year‐1 respectively in the periods
of 1999‐2002 and 2002‐2005 (Dislich et al. 2002; Zupo and Pivello 2007; Silva
Matos and Pivello 2009). By 2005, the species represented almost one third of the
forest patch trees and the diameter distribution curve indicated an ongoing
expansion process.
Euterpe edulis Martius (Arecaceae), known by its tasty palm heart, is native
to the Southeastern Atlantic rainforest and originally occurred in large forested
areas, but today it is extinct in most of its original region (Galetti and Aleixo
1998; Galetti and Fernandez 1998). Its fruits are spherical black drupes with a
thin epicarp and fibrous mesocarp (Henderson and Galeano 1996), being
available from December to September (Silva Matos and Watkinson 1998). This
species is mostly used as a food delicacy (palm heart and pulp), but also as
ornamental (Lorenzi et al. 2004). In this last case, it performs not only as an
aesthetic element but also as important food source to the frugivore fauna being
60
considered a keystone species (Galetti and Aleixo 1998; Silva Matos and
Watkinson, 1998). The population decline of some Atlantic forest birds is
attributed to the devastation of this native palm tree (Galetti and Aleixo 1998),
therefore, it has a key role on the preservation and restoration of southeastern
Atlantic forest remnants (Reis et al. 2000).
Fruit sampling and processing
In the experiments we used only the kernels (hereafter generically called
seeds, although containing the endocarp attached to them) of both species
mature fruits, sampled at different times and localities (Table 1). A.
cunninghamiana fruits were collected from at least ten planted ornamental
matrices, while E. edulis fruits came from tens of matrices of natural occurrence.
Fruits were soaked in water at room temperature (± 25ºC) during 24 hours, after
that being mechanically depulped and dried at shade (Brasil 1992a; Meerow
2004). The seeds were then used for the “seed burying” and “seedling
establishment” experiments.
Seed viability
Viability tests were carried out before and after the experiments, using
non‐germinated and intact seeds. The seeds had their embryo mechanically
exposed by a longitudinal cut and, after that, they were soaked in Tetrazolium
salt solution (2,3,5 triphenyl chloride) at 0.5% for 5 hours in the dark, at 30ºC
(Brasil 1992b; ISTA 1993). The viability was visually determined: seeds were
considered viable when showing a light reddish color in more than 50% of the
embryo (Biagioni and Godoy 2005), and those with the embryo physically
deformed, uncolored or intensely red colored were considered non‐viable
(França‐Neto et al. 1998).
Seed rain
61
Twenty‐five 3 x 2 m seed traps were randomly placed in a 2.1 ha area inside
the forest reserve, at least 5 m apart, comprising a sampled area of 150 m2. The seed
traps were built with 5 mm nylon mash and placed 80‐90 cm above ground. All
seeds caught in the traps were collected every 40 days during one year (March 2009
to February 2010). Only the diaspores (fruits and seeds) larger than 5 mm were
counted, and classified as: anemochoric or non‐anemochoric (= mainly zoochoric),
and also as native or alien species (this last class identified to the lowest taxonomic
level).
As we had previously observed that the invasive palm species becomes
reproductive in full sun (such as in the university gardens and forest gaps), we
performed linear regressions to test for a possible spatial relationship between
seed density in the trap and the seed trap distance from both the forest borders
and the stream in the middle of the forest patch, which represents a natural gap
(Figure 1). The results could indicate whether seeds entering the forest were
more related to the ornamental matrices in the gardens or to matrices already
established inside the shaded forest. The independent factor was the smallest
distance (calculated on a GIS program) between the seed trap and the forest
closest border or the stream, and the dependent factor was the cumulative
number of seeds in each trap at the end of 12 months.
Seed longevity (seed burying experiment)
As palm species seeds usually do not show physiological dormancy – but
a slow germination due to its undeveloped embryo (Baskin and Baskin 2001;
Meerow 2004) – an useful way to determine if seeds are persistent (i.e. maintain
viability) at soil level is by performing a controlled seed burying experiment to
test seed longevity in loco (Lunt 1995; Thompson et al. 2003; Oliveira et al. 2006).
62
That method allows estimating the potential species soil seed bank (Bakker et al.
1996).
Seed burying tests in the forest soil with A. cunninghamiana and E. edulis
seeds were performed in March 2009 in two randomly selected areas free of any
direct human interference. In each area, 12 replicates of nylon fabric bags
containing 30 seeds of either A. cunninghamiana or E. edulis plus sieved forest soil
were buried at 3 cm depth and located at least 3 m apart. Four replicates of each
species were retrieved from soil after 3 (June 2009), 6 (September 2009) and 12
(February 2010) months after being buried. Seeds from the bags were classified as
germinated (seeds with visible coleoptile), seedlings (appearance of the first
eophyll), non‐germinated, and dead. Seeds classified as non‐germinated were
submitted to the viability test (Lunt 1995; Oliveira et al. 2006).
Seedling establishment
We set up 33 2 x 2 m randomly distributed blocks along the 2.1 ha forest
area, located at least 3 m apart. We did not put blocks at steep slopes in order to
prevent seeds of being washed away by rainfall. All blocks were divided into
two 2 x 1 m experimental plots, and received the same treatment: initially we
removed seeds, seedlings and juveniles of A. cunninghamiana from both
experimental plots. Since A. cunninghamiana does not impose allelopathic or
competition effects on E. edulis germination (A.L.T. Mengardo and V.R. Pivello,
unpublished data) both species were sown together. We sowed 20 depulped
seeds from both A. cunninghamiana and E. edulis in one of the two plots. The
adjacent plot was kept without sowing as control. Both blocks were covered with
a white nylon mash (5 mm), approximately 80 cm above soil surface, to prevent
the interference of natural seed rain in the experiment. To encourage germination
63
we sowed in November, when the wet summer season begins and soil moisture
is high (Silva Matos and Watkinson 1998).
Seedling emergence and survival were monitored in those plots for 12
months (December 2009 to November 2010). The number of emerged seedlings
of both palm species was monthly counted and seedling growth was monitored.
To compare the number of emerged seedlings of both palm species (native x
exotic) we performed a parametric t test, using the software Statistica 7.0.
Results
Seed rain
Eight seed rain countings were carried out during the study period, and
42,836 diaspores were collected (density of 278.7 diaspores m‐2) and classified in
54 morphotypes. Four morphotypes corresponded to alien species: A.
cunninghamiana, Eucalyptus sp., Pinus sp. and Tipuana tipu, but the contribution of
these exotic species other than A. cunninghamiana was small, with only 15 seeds
in 12 months. Native species comprised 41,806 of total diaspores, and those with
anemochoric dispersal syndrome (excluding alien species) were the most
abundant: the top three morphotypes were native and anemochoric, accounting
for 91.45% of total diaspores (39,170 diaspores). A. cunninghamiana was the fourth
most abundant species and the first in the non‐anemochoric class, represented by
1,015 seeds (2.37%) that corresponded to 6.77 seeds m‐2 year‐1. Most A.
cunninghamiana seeds (912 seeds) were collected in the summer months
(November to February). Considering only the non‐anemochoric (mostly
zoochoric) diaspores the relative abundance of A. cunninghamiana reached
33.60%.
64
No relationship was found between the number of A. cunninghamiana
seeds and the seed trap distance from the forest edge (F1,23=0.00129; R²=0.0006;
p=0.97) or the stream (F1,23=0.0306; R²=0.001; p=0.86).
Seed viability and longevity
Initial viability tests showed more than 80% of A. cunninghamiana seeds
viable in the October sampling, while that value was around 60% for E. edulis
(Table 1). Three months after being buried (June), respectively 35.83% and 9.17%
of A. cunninghamiana and E. edulis seeds germinated (Table 2). Moreover, around
40% of the non‐germinated seeds of both species remained viable indicating a
potential to later germination (Table 2). After six months (September)
approximately 90% of A. cunninghamiana seeds germinated and 3.33% had
become seedlings, showing unexpectedly high germination performance (Table
2) compared to that predicted by initial seed viability test (Table 1). In contrast,
35% of E. edulis seeds germinated after six months, and no seedlings had yet
emerged after that time, but more than 30% of non‐germinated seeds were still
viable. After one year, E. edulis showed percentages of both germinated seeds
and seedlings around 30%, while 68% of A. cunninghamiana buried seeds had
become seedlings and no more seeds germinated. Since that last removal showed
no viable seeds of both species among the non‐germinated ones we can state that
they do not maintain viability longer than 12 months.
Seedling establishment
Still, A. cunninghamiana produced a significantly higher number of
seedlings per month compared to E. edulis (df=14; t=5.40; p<0.01), reaching 5.54
seedlings m‐2 and indicating that more than 50% of the sowed seeds became
seedlings, while E. edulis produced at most 1.21 seedlings m‐2 (Figure 1). Both
species increased seedling production along time, but then the number of E.
65
edulis seedlings dropped to almost half a few months after being sowed, while
the exotic palm maintained not only a higher density but also kept increasing
seedling production up to the end of summer (March‐April). After dropping
seedling density due to early mortality, A. cunninghamiana still maintained a
density of about 4 seedlings per m2, while that value for E. edulis was less than
one seedling per m2. The final density of A. cunninghamiana seedlings after one
year was 3.03 seedlings m‐2 (30.3% of seedling survival, related to the number of
sowed seeds), and of E. edulis was 0.35 per m2 (3.5% of seedling survival),
The adjacent control plots showed neither seed germination nor seedling
production of both species, indicating that results in the experimental plots were
only due to the sowed seeds, with no interference of outsider diaspores of these
two palm species in the experimental plots.
Discussion
The seed rain estimation showed that approximately 279 diaspores m‐2 can be
dispersed in the studied forest patch during one year, a value within the range
reported to other tropical forests (Drake 1998; Pivello et al. 2006). Considering the
non‐anemochoric diaspores (basically zoochoric species) we found a density of
13.31 m2, and almost half of these diaspores belonging to A. cunninghamiana (6.77
seeds m2, or 33.60%). This proportion is a very high value for only one species,
and represents a high propagule pressure over the forest patch. The ability to
produce a great amount of diaspores that can efficiently disperse is a key trait for
the success of invasive species (Rejmánek 1996). Such attribute is positively
associated with the species establishment (Colautti et al. 2006; McAlpine and
Jesson 2008) – especially concerning shade‐tolerant species – and increases
chances of bioinvasion in tropical forests (Fine 2002). A. cunninghamiana fits to
66
that pattern since its fruits are produced in a great quantity throughout the year
(Mengardo and Pivello 2007). In fact, A. cunninghamiana seeds were present in
the seed rain all year round and without any spatial relation to the main seed
sources, such as stream areas and forest edges. Although the bioinvasion process
in the study area began from the ornamental matrices planted in the surrounding
gardens, there is no longer a higher propagule pressure coming from outside the
forest. This is probably because reproductive individuals can already be found in
the inner parts of the forest patch, confirming the high invasibility of that alien
species and its effective dispersal by fauna.
Compared to E. edulis, A. cunninghamiana showed a better performance in
germination and seedling production: in the burying experiment it showed a
germination rate almost four times higher after three months, and reached 90%
against 35% of E. edulis after six months. The removal of seeds after being one
year buried showed that approximately 68% of A. cunninghamiana seeds had
become seedlings, against less than 30% of E. edulis. We had already observed
high germination rates of A. cunninghamiana in laboratory conditions, more than
twice the value reached by E. edulis (A.L.T. Mengardo and V.R. Pivello,
unpublished data). Still, a higher success on seedling production of both palm
species was achieved when seeds were buried compared to seed sowing. Even
taking into account the different conditions of these experiments we consider
that buried seeds may face more stable microclimatic conditions, e.g. moist and
temperature. Moreover, it is possible that the bags served as a barrier against
larger predators like granivorous vertebrates. Both species did not form
persistent seed banks, since every seed germinated or died within a year (Bakker
et al. 1996; Baskin and Baskin 2001).
67
Besides its higher germination rates and seed viability, A. cunninghamiana
also showed faster germination compared to E. edulis. The seeds of this native
palm reached a maximum germination rate of nearly 50%, a value coherent with
the results of the initial viability tests, and also similar to those found in other
studies (e.g. Bovi and Cardoso 1975; Silva Matos and Watkinson 1998),
confirming a similar establishment potential in non‐invaded Atlantic forest
patches.
Our results showed that A. cunninghamiana seeds came mainly through
the seed rain rather than from soil seed bank, revealing its typical transient seed
bank (Drake 1998). However, as the species fructifies all year round, newly
dispersed seeds can always be found in the surface soil. It is advantageous for an
invasive species to produce such short‐lived seeds that massively germinate,
especially when combined with effective spatial dispersal (McAlpine and Jesson
2008). Thinking about management strategies for that invasive palm species we
may consider this kind of transient seed bank strategy advantageous. So, the
removal of A. cunninghamiana reproductive individuals may be sufficient to stop
the invasion process, because seeds would no longer be dispersed and new
seedlings would not emerge from the soil seed bank in a medium/long term. On
the other hand, the native species also showed the same strategy, which makes
its reintroduction in the habitat more difficult. Therefore, periodic introduction of
seeds (simulating the annual dispersion) would be necessary to restore E. edulis
establishment until individuals reach maturity and begin to produce fruits.
Considering the establishment of both species seedlings in the invaded
site, A. cunninghamiana overwhelmed E. edulis again by producing significantly
more seedlings throughout the study period. Taking the density of A.
cunninghamiana obtained in the seed rain and the probability of its seedlings to
68
survive after one year, we can estimate that this species is able to establish about
two seedlings m2 one year after dispersion, with no viable non‐germinated seeds
remaining in the soil. In the study site, this could result in nearly 200,000 new
individuals per year, illustrating the enormous pressure over the native
community. Moreover, we confirmed that E. edulis recruitment capacity is very
low (weak germination and less than 5% seedling survival) compared to that of
the invasive palm, what weakens its competitive ability in the early demographic
stages at an invaded forest.
The enemy release hypothesis is one possible explanation to the great
performance of A. cunninghamiana concerning germination and seedling
establishment, and also a survival rate almost ten times higher than that of the
native palm at these first demographic phases – a fact already registered for other
alien species in invaded habitats (Ferreras and Galetto 2010). This hypothesis
assigns the success of invasive species to the inexistence of natural enemies, such
as pathogens and herbivores in the new habitat, and thus benefits plant
performance especially in the early life stages, (Keane and Crawley 2002; Bais et
al. 2003; Dostál 2010). There are some examples of tree species in natural and
newly invaded habitats showing that some fitness parameters are incremented in
the new habitat due to the lack of native parasites and predators (Mack et al.
2000). However, in our case study this is a conjecture and has to be verified.
Euterpe edulis, on the other hand, is known for its low performance at the
first demographic stages, showing a pyramid‐shape demography that suggests
low germination rates and increasing post‐germination mortality (Reis et al.
2000). Such attributes, in addition to low seed viability and high seedling
mortality at smaller sizes (the first stages of seedling sprout) were corroborated
in this study, and resulted in less than 10% of seedling survival after one year.
69
However, Silva Matos et al. (1999) found a survival rate of E. edulis seedlings in a
non‐impacted Southeast Atlantic forest area around 50%. Hence, in order to
increase the population in areas deprived of this species we propose the sowing
of a high number of seeds or even the transplant of juveniles, a more laborious
approach which assures higher survival success, as the individuals would have
overcome the most difficult establishment phase (McAlpine and Jesson 2008).
Silva Matos et al. (1999) showed that survival probability increases with growth,
achieving a maximum when juveniles reach a diameter at soil level of 30 to 60
mm. Those authors also found in the non‐invaded Southeastern Atlantic forest
an average density of E. edulis adults of 0.71 trees.m‐2. In our experiment, in
which we sowed 10 seeds m‐2, the final density of E. edulis seedlings after one
year was only 0.35 m‐2, already half the value of the adults found in the
conserved forest, predicting an impoverishment of adult individuals in the
studied area.
Yet, the alien palm tree showed a different pattern in the early life stages
compared to the native one: It exhibited a high germination rate and produced a
corresponding number of seedlings, maintaining a high number throughout the
year. Van Kleunen et al. (2010) also found higher performance at the early stages
as a pattern of the invasive species when compared with the natives. Even
though the survival rate of A. cunninghamiana seedlings was around 30%,
meaning that almost three quarters of the sowed seeds could not continue the
establishment process, this value can be considered high since seedlings
naturally have a very high mortality (McAlpine and Jesson 2008). This is an
important information for management as it shows that seedling control is not
necessary because more than half of the invasive seedlings will naturally die.
70
Conclusion
A. cunninghamiana showed a high number of dispersed seeds, with no
spatial dispersion restriction. Such a high propagule pressure on the community
is a trait typically associated to bioinvaders. Nevertheless, that alien palm did not
form a persistent seed bank. No difference was found in the longevity of both E.
edulis and A. cunninghamiana seed banks, what is suitable for managing the
invasive species but disfavors E. edulis permanence in the community.
Additionally, A. cunninghamiana seedling establishment was more successful
than that of E. edulis, another feature that favors bioinvasion (Daehler 2003).
To reintroduce E. edulis in the invaded forest patch, a single seed sowing
seems to be ineffective as its seeds do not last long in the soil and seedling
establishment is low. A refinement of this approach would be the periodical
introduction of seeds to increase the initial propagule pressure of the native palm
on the community, or the transplant of juveniles. These actions could promote
higher chances of successful E. edulis establishment and its future self‐support ,
no longer requiring further human intervention.
Acknowledgements
The authors wish to thank Mauricio Perine and Paulo César Fernandes for field
assistance, Dr. Nelson Augusto Santos for helping on diaspores identification
and Dra. Alessandra Fidelis and Alexandre Igari for valuable suggestions on this
manuscript. This study was supported by FAPESP (Fundação de Amparo à
Pesquisa do Estado de São Paulo, proc. 2008/56015‐8).
71
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Table 1: Information about seeds of both species used in this study: the sampling
date and locality, initial viability, and type of experiment in which the processed
seeds were used. (B= burying experiment; S= seedling establishment experiment).
Species Date Local Viability Experiment Archontophoenix
cunninghamiana April 2009
Universidade de São Paulo, São Paulo, SP
(23°33’57”S and 46°43’43”W) 56.06%
B
October 2009
Universidade de São Paulo, São Paulo, SP
(23°33’57”S and 46°43’43”W) 84.80%
S
Euterpe edulis April 2009
Instituto Florestal, São Paulo, SP
(23°27’34”S and 46°37’54”W) 49.06%
B
October 2009
Neblinas Park, Mogi das Cruzes, SP
(23°44’07”S and 46°11’05”W) 60.20% S
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Table 2: Percentages of seeds found in each class, from the total of 120 retrieved
at every phase (after three, six and 12 months) of the burying experiment in the
forest (initiated in March). Viability tests were made with only the seeds
classified as non‐germinated.
3 Months
(June) 6 Months
(September) 12 Months (February)
A. cunninghamiana Dead 10.83 4.17 31.67 Germinated 35.83 90.83 0 Seedlings 0 3.33 68.33 Non-germinated non-viable 12.50 0.83 0 viable 40.83 0.83 0
Total 99.99% 99.99% 100% E. edulis
Dead 23.33 13.33 44.17 Germinated 9.17 35 26.67 Seedlings 0 0 29.17 Non-germinated non-viable 28.33 19.17 0 viable 39.17 32.50 0
Total 100% 100% 100.01%
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Figure 1: Location of the studied Forest Reserve (Universidade de São Paulo, São
Paulo city, SP, Brazil).
Figure 2: Cumulative density of Archontophoenix cunninghamiana and Euterpe edulis seedlings after sowing seeds in the
forest floor, from December 2009 to November 2010 (10 seeds m‐2 of each species were sowed).
0
2
4
6
Dec Jan Feb Mar May Jun Aug Nov
See
dlin
gs d
ensi
ty (s
eedl
ings
/m 2 ) A. cunninghamiana E. edulis
Discussão Geral e Conclusões
Plântulas (ao fundo) e sementes da palmeira juçara (Euterpe edulis) no solo de um fragmento florestal de Mata Atlântica no Parque Estadual das Fontes do Ipiranga, São Paulo. Foto: Ana Luisa Mengardo.
83
Neste estudo, visamos subsidiar um plano de manejo para uma reserva
florestal de Mata Atlântica impactada por um processo de invasão da palmeira
australiana Archontophoenix cunninghamiana. Para isso, realizamos estudos em
campo, numa área degradada e impactada pela invasão biológica, a fim de
termos melhor representado o contexto do problema. Além disso, fizemos
experimentos em laboratório para obtermos resultados sob condições
controladas. Pudemos, então, comparar as duas abordagens de experimentos, o
que nos trouxe maior riqueza de dados e possibilitou a formulação de sugestões
para o manejo de fragmentos florestais invadidos. Procuramos, ainda, utilizar
métodos e materiais que fossem factíveis em uma área natural, visando maior
sucesso na implementação das ações de manejo. Além disso, escolhemos
trabalhar com uma espécie nativa taxonomicamente próxima da espécie invasora
(mesma subfamília), ambas também pertencentes à mesma sinúsia. Isto pôde
evitar uma possível atribuição errônea das causas dos resultados obtidos, já que,
em casos de espécies ecologicamente distantes, os diferentes atributos e/ou
aptidões podem estar relacionadas com suas diferentes formas de vida e não
serem resultantes da interação propriamente dita (Vilà & Weiner 2004).
Nossa proposta, portanto, foi a substituição da palmeira australiana
invasora Archontophoenix cunninghamiana pela palmeira nativa Euterpe edulis
(juçara). Esta espécie, além de ser nativa e endêmica da Mata Atlântica, tem
importância tanto para a comunidade animal (sendo considerada uma espécie‐
chave) quanto para o homem, que se utiliza de sua matéria prima (tronco, folhas,
palmito, frutos) para diversos fins (alimentação, construção, ornamentação, etc).
Além de sua importância, há uma urgência em se preservar a E. edulis também
devido ao elevado grau de ameaça em que se encontra. Projeções considerando
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situações resultantes das mudanças climáticas globais indicam que a palmeira
juçara diminuirá em ocorrência nas florestas da Mata Atlântica, de 12,9% (cenário
mais otimista) até 59,2% (cenário mais pessimista), destacando a importância de
projetos atuais que visem sua conservação (Colombo & Joly 2010). Porisso, esse
estudo também explorou uma possível reintrodução dessa espécie em áreas
degradadas, visto que ela é capaz de mudar os rumos da dinâmica sucessional
quando presente na comunidade florestal (Reis & Kageyama 2000).
Comparativamente, obtivemos como resultados não só taxas maiores de
sementes viáveis e de germinação, mas também um melhor estabelecimento de
plântulas da palmeira invasora frente à palmeira nativa, o que favorece a
perpetuação da primeira em detrimento da juçara numa situação de
reintrodução. Por outro lado, verificamos que o manejo das áreas invadidas pode
ser planejado sem preocupação com a liberação de substâncias alelopáticas das
folhas e frutos da espécie invasora, que poderiam inibir o desenvolvimento da
palmeira nativa ou de outras espécies co‐ocorrentes.
Alguns atributos observados, tais como elevada produção de sementes e
eficiente dispersão, a alta germinabilidade e o curto intervalo entre produções
massivas de sementes, são características típicas que favorecem a invasão e
determinam espécies invasoras bem sucedidas (Rejmánek 1996). Desta forma,
nossos resultados ajudaram a explicar o alto desempenho e o sucesso de invasão
da A. cunninghamiana em áreas florestais.
A semeadura direta de ambas as espécies em ambiente natural, aqui
realizada com a finalidade de simular uma reintrodução da palmeira nativa na
presença da invasora, indicou que utilizamos um número inadequado de
sementes por área (que resultou numa densidade de 10 sementes.m‐2). Isto,
somado ao massivo input natural de sementes provenientes da espécie invasora –
85
que é a espécie zoocórica identificada, por meio da chuva de sementes, como
tendo o maior número de propágulos dispersos ao longo do ano dentro da
floresta – dificultaria ainda mais o restabelecimento de E. edulis numa situação
semelhante à do fragmento invadido estudado. Portanto, refinamos algumas
ações propostas para melhorar o sucesso da reintrodução, como o transplante de
indivíduos jovens da palmeira nativa, ou a semeadura periódica de suas
sementes, principalmente nos períodos mais úmidos do ano.
Os dois capítulos demonstraram que o re‐estabelecimento da palmeira
juçara em fragmentos florestais invadidos será ineficiente se depender apenas do
recrutamento pelas sementes através de uma semeadura direta. Essa dificuldade
em se estabelecer ocorrerá independentemente da presença da palmeira invasora
e dos seus possíveis efeitos diretos ou indiretos sobre o desenvolvimento nos
estágios demográficos iniciais da espécie nativa. Deste modo, a baixa taxa de
recrutamento da espécie nativa deveu‐se ao seu gargalo demográfico natural e
não a interações com a espécie invasora.
Para a conservação in situ da juçara, além de uma introdução bem
sucedida, a regeneração natural deve ser alcançada em longo‐prazo, pois é parte
crucial para o efetivo processo de manutenção e colonização da população
(Conte et al. 2000). Portanto, deve‐se priorizar o sucesso na reintrodução que
chegue até o ponto no qual haja uma regeneração natural da espécie sem
intervenções humanas diretas, o que asseguraria sua auto‐sustentação no habitat
original.
Os resultados também demonstraram que uma das formas para conter a
regeneração da palmeira invasora seria manter os frutos com a polpa carnosa
envolvendo as sementes. Isto poderia ser feito cortando‐se os cachos e deixando‐
os no solo da floresta, uma ação de manejo pouco custosa e relativamente pouco
86
trabalhosa. Esses frutos permaneceriam no solo num estágio anterior ao consumo
pelos frugívoros, e, nesse estado, seu sucesso na germinação e formação de
plântulas é significativamente inferior se comparando com as sementes
despolpadas. Por fim, sugerimos que as ações voltadas ao manejo de A.
cunninghamiana dirijam‐se prioritariamente aos indivíduos reprodutivos, já que a
espécie não mantém um banco de sementes duradouro no solo da floresta, mas
frutifica abundantemente ao longo do ano todo.
A grande importância de estudos como este, que visam subsidiar o
manejo em áreas de floresta nativa, reside no fato de contribuírem para a
promoção de ações mais eficazes de mitigação de impactos, visando à
conservação da biodiversidade em fragmentos florestais.
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Apêndices
Appendix I