CerradoSouth America- BrazilMoist Savanna Site

Dr. Dulce Alves da Silva

(University of Brasilia)

Cerrado

• Covers 2 million Km2

• Approximately the size of Western Europe

• Cerrado in Portuguese = closed, dense

Typical Vegetation Landscape

• Savanna of very variable structure, termed cerrado sensu lato :– Well-drained soils,– Avoiding valley bottoms

• Other vegetation: – Patches of base-rich soils. Ex: Mesophytic Forests– Soil prone to water logging for

considerable periodsEx. Gallery forest: vegetation following the

watercourses

Distribution of Cerrado Vegetation• Seasonal precipitation

– Which cannot entirely explain the predominance of Cerrado vegetation,

– Present climatic conditions would favor the establishment of forest in most of the Cerrado Biome region

Other explanations:• Soil fertility• Soil drainage • Fire regime

Climate

• Variable: big area • Mean Temperature: 18º to 28ºC• Rainfall: 800 to 2,000 mm

– Intense dry season

(April – September)

Mosaic of Physiognomies

Encompasses a series of vegetation physiognomies from open grasslands to dense woodlands

Vereda

Gallery forest

Campo Sujo

Cerrado sensu stricto• Dominated by trees and shrubs often 3-8

m tall • Provides more than 30% crown cover • Still a fair amount of herbaceous

vegetation between them

Cerradão• Almost closed sclerophyllous woodland • Crown cover 50 to 90%• Trees 8-12 m • Ground layer much reduced

PhysiognomiesSavannic Physiognomies

• Ex. Campo limpo, Campo sujo, cerrado sensu stricto, cerradão– Predominate in the landscape– Well-drained Soil – Low-fertility soils – Sclerophylly is common– Mixture of plants of two fairly distinct layers

with features of pyrophytic savanna vegetation:

• Woody layer: trees and large shrubs• Ground layer: subshrub and herbs

Savanna

Ground Layer

• Herbs, subshrubs and smaller shrubs

• Much richer than trees and large shrubs

• Castro et al. (1999): 6,836 spp

Woody layer• Trees:

– with low contorted form – with fire-resistant bark– Leaf phenology: Deciduous, brevi-decidous and evergreen

species

• Hydraulic lift: passive movement of water from drier to moister portions of the soil profile via root systems (Jackson et al. 1999)

– Can contribute to the water balance of neighboring plants

• 1,000-2,919 tree/shrubs species (Ratter & Ribeiro 1996, Castro et al. 1999)

• High Local diversity of trees and large-shrubs:– Alpha diversity = 100 - 150 species per hectare

(Ratter et al. 2003, Felfili et al. 2004)

• Aluminum is extremely toxic to most cultivated plants• Most native species are aluminum-tolerant (Haridasan 1982,

Haridasan et al. 1986)

Woody Species

Woody Species• Most important families in terms of species numbers:

– Leguminosae (153 spp, all 3 subfamilies)– Malpighiaceae (46 spp.)– Myrtaceae (43 spp.),– Melastomataceae (32 spp.)– Rubiaceae (30 spp.)

• Many areas of vegetation dominated by Vochysiaceae (23 spp.).• Abundance of 3 species:

– Qualea grandiflora– Qualea parviflora– Qualea multiflora

• Largest Genera:– Byrsonima (Malpighiaceae, 22spp.)– Myrcia (Myrtaceae, 18 spp.)– Kielmeyera (Guttiferae, 16 spp.)– Miconia (melastomataceae, 15 spp.) – Annona (Annonaceae, 11 spp.)

• High regional diversity• 315 sites• 914 species (trees and shrubs)• 300 species occur at 8 or more sites (i.e. ≥2.5%

of the total ), while the remaining 614 species, including 309 unicates, are very rare.

Bioma Cerrado: Main Regions according to the

composition

• C & SE: Central and south-eastern;

• CW: Central-Western;

• FWM: Far western mesotrophic sites

• N & NE: North and North-eastern

• S: Southern

Ratter et al. (2003)

Intense Human Pressure

• Conversion of mixture of trees and grasses to predominantly herbaceous vegetation– Expansion of agriculture– Grazing lands– Anthropogenic burning disturbance (igniting the

majority of present fires in tropical savannas)• Climate change: indirectly influence through

changes in the frequency of fire due to alterations in the fuel load

Brazilian Hotspots• 2 hotspots: Atlantic Forest and “Cerrado”

– Among 25 global biodiversity “hotspots” of absolute importance for conservation (Myers et al. 2000)

– Conservation efforts in the Cerrado have not achieved international = standards 1.6 % (Amazon ~6%) (Cavalcanti & Joly 2002)

Fire• Burning occurs at intervals of 1-3 years –

a rate that exceeds the precolonization fire regime

• Frequently used management tool (Pivelllo & Coutinho 1996)

• Most of the savannic flora are fire-adapted species

• However, now subjected to frequencies in excess of the environment in which they evolved

• Gallery forest species are not fire adapted• Recurrent fires tend to: result in soil

impoverishment

Fire

• Affects all aspects of the demography of Cerrado plants, reducing (Hoffmann 1996, 1998, 2000)

• Fire induce reversions of woody species from larger to smaller size classes

• Frequent fire damage favors the ground layer = Producing more open physiognomies

Seedling in Cerrado• Main restriction:

– Frequent fire– Low nutrient availability– “Veranico”: unpredictable dry spells in the wet

season (Hoffmann 1996, Nardoto et al. 1998)– Prolonged drought (dry season)– Herbivory

• Vertebrates (Nardoto et al. 1998)

• Invertebrates (personal observation)

– Competition mainly with grasses• Native species

• Exotic species (Hofmann et al. 2004)

Size vs TimeSpecies Plant size (cm) Plant age (years)

Bowdichia virgilioides 8.3 (0.5) 2

Dalbergia miscolobium 23 (2.7) 7

Kielmeyera coriacea 2.3

2.7

2.8

8.3 (1.8)

1

2

3

5

Qualea grandiflora 5.3 (0.3) 1

(Franco 2002, Nardoto et al. 1998)

• Seedling develop a tree canopy layer in the grass matrix through a slow process

Seedling vs Fire

• For 7 of 12 species establishment success of experimentally placed seeds was found to be:– Lower in recently burned sites– No enhanced establishment when burnt 1 or

more years previously

Seedlings in Cerrado

Ex. Kielmeyera coriacea– Seeds: not dormant (<20 days), but with short

viability– First year:

• Rainy season (after 3 months of transplantation) “veranico” – negative impact

• First dry season: was not a major influence on survival:

– Second year: • 35% of surviving plants were removed by

armadillos (Dasypus spp) (Nardoto et al. 1998)– When the interval between fires is not enough to

reach a fire-tolerant size, seedlings re-sprout and form “seedling bank” (Oliveira & Silva 1993, Nardoto et al. 1998).

Root system in Cerrado Seedling

Taproot– Early growth (high root/shoot rate) – Stores carbohydrate permit re-sprouting following fire,

drought or herbivory– Root length to access water in deeper soil water:

Stryphnodendron adstringens and Qualea grandiflora ~55 cm (greenhouse experiment - 7 months) (Moreira & Klink 2000)

– Water potential at 60 cm depth did not drop below -1.6 MPa, indicating a permanent source of water within

reach of deep taproot (Franco et al. 1996)

(Hoffmann & Franco 2003)

Fire Re-sprout

• Species also are able to re-sprout after fire:– 8 out of 9 savanna species were able to

survive fire when less than 1 yr old (Hoffmann 2000).

– Survival of burned seedling was positively correlated to seed mass

Light

– Grass vs Seedlings - Assimilation rate in Kielmeyera coriacea:

• 5 cm high plants range between 26 to 40 % of photosynthetic capacity

• 50 cm (not hide by grass layer): 80% of photosynthetic capacity (Nardoto et al. 1998)

– Growth of many species did respond to light level, with the effect being positive for some species and negative for others (Hoffmann & Franco 2003)

Cotyledons• Play an important role in seedlings

establishment: 1 to 6 months

(Nardoto et al. 1998, Sassaki & Felippe 1992)

Nutrient vs Seedlings

• There is an overall positive effect of nutrients on RGR

• There is no light–nutrient interaction(Hoffmann & Franco 2003)

Woody Density

• Cerrado seedlings less dependent on woody cover than gallery forest species (Hoffmann 2000). – Soil under trees might:

• Have better nutrient status• Higher moisture content during dry periods than

open grassland• Reducing the density of the competing herbaceous

layer

Species choice

• Common species

• Seed availability

• Seed viability

• None of the species belong exclusively to a particular Cerrado community

Grass Species

Echinolaena inflexa:

• common species in different communities

• C3

• rhizomatous or loosely tufted short-lived

• perennial grass

• 20-50 cm high

Woody Species

• Dalbergia miscolobium

• Dimorphandra mollis

• Pterodon pubescens

• Kielmeyera coriacea

• Qualea grandiflora

• Eugenia dysenterica

Need better characterization

• Effects of litter • Effects of grass competition for nutrients• The influence of mycorrhiza in seedlings

establishment • The impact of herbivory in the seedling

establishment• How environmental changes will have an impact

in grasses and seedlings competition:– light, nutrients, fire

Thank You