Effects of fertiliser and grazing on the arthropod communities of a native grassland in south-eastern Australia

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Agriculture, Ecosystems and Environment 109 (2005) 323–334

Effects of fertiliser and grazing on the arthropod

communities of a native grassland in

south-eastern Australia

Ian Oliver a,*, Denys Garden b, Penelope J. Greenslade c,Bronwyn Haller a, Denis Rodgers d, Owen Seeman e, Bill Johnston f

a New South Wales Department of Infrastructure, Planning and Natural Resources, PO Box U245,

University of New England, Armidale, NSW 2351, Australiab New South Wales Department of Primary Industries, GPO Box 1600, Canberra, ACT 2601, Australia

c Division of Botany and Zoology, Australian National University, Canberra, ACT 0200, Australiad 19 Amaroo Avenue, Ferny Hills, Qld 4055, Australia

e PO Box 3300, The Queensland Museum, South Brisbane, Qld 4101, Australiaf New South Wales Department of Infrastructure, Planning and Natural Resources,

PO Box 365, Queanbeyan, NSW 2620, Australia

Received 13 January 2004; received in revised form 18 February 2005; accepted 21 February 2005

Abstract

An experiment commenced in 1998 to test the effects of superphosphate fertiliser application and grazing on production

and botanical composition of a native grassland in south-eastern Australia. Superphosphate application resulted in an

increase in sheep production but a decline in native perennial grasses and an increase in exotic annual grasses. The study

reported here aimed to determine if arthropod assemblages showed changes in community composition on the same

experimental plots. The experiment was conducted in grassland dominated by the native perennial wallaby grass,

Austrodanthonia duttoniana, and consisted of six replicated treatments that were designed to improve grassland and

domestic livestock productivity. Treatments consisted of a control (no fertiliser), three levels of annually applied super-

phosphate (62.5, 125, and 250 kg ha�1), and two treatments aimed to raise soil pH (superphosphate plus lime, and sewage

ash). Soil properties were measured annually and sheep stocking rates were increased over the duration of the experiment

according to increases in available forage. Soil and ground-active arthropod populations were sampled from all plots in

spring 2001. Fertiliser application and grazing increased the relative abundance of introduced Acari and Collembola, and

changed the community composition of Formicidae and Coleoptera. Lime and sewage treatments had variable effects on

taxa. Improving the productivity of native grassland with superphosphate led to a decline in plant and arthropod biodiversity

through reduced abundance and/or local extinction of native species and increased dominance of introduced species. These

* Corresponding author. Tel.: +612 6773 5271; fax: +612 6773 5288.

E-mail address: [email protected] (I. Oliver).

0167-8809/$ – see front matter. Crown Copyright # 2005 Published by Elsevier B.V. All rights reserved.

doi:10.1016/j.agee.2005.02.022

I. Oliver et al. / Agriculture, Ecosystems and Environment 109 (2005) 323–334324

findings support the need to protect and restore a representative network of native grassland ecosystems within the

agricultural zone of south-eastern Australia.

Crown Copyright # 2005 Published by Elsevier B.V. All rights reserved.

Keywords: Native grassland; Fertiliser; Lime; Sewage; Grazing; Arthropod biodiversity; Acari; Collembola; Coleoptera; Formicidae; Exotic

species

1. Introduction

Within Australia’s Murray-Darling Basin the major

land use is domestic livestock grazing. Because

Australian soils are relatively low in phosphorus

(P), sulphur (S) and nitrogen (N) (King and

Hutchinson, 1983), native grassland may be improved

through the addition of P and S as superphosphate, and

N fixed by sown legumes (King et al., 1985). To raise

the pH of soils and increase productivity, liming has

also become more common in recent years.

Native grasslands and their soils contain large

numbers of arthropods, the biodiversity of which is

vitally important to production systems (Srivastava

et al., 1996; Vietmeyer, 1996; Altieri, 1999; Paoletti,

1999; CSIRO, 2001). The impacts of fertiliser

application and associated increases in stocking

intensity on arthropod biodiversity can vary by

location and taxa (Zyromska-Rudzka, 1979; King

and Hutchinson, 1980; King et al., 1985; Berger et al.,

1986; Carlyle and Than, 1987; Vickery et al., 2001). In

Australia, King and Hutchinson (1980) found an

increase in mite and collembolan populations follow-

ing superphosphate application. Zyromska-Rudzka

(1979) found that scutacarid mites decreased in

abundance after NPK fertilisation of a Polish meadow,

while oribatid mites increased, whereas Olechowicz

(1977) found application of NPK fertiliser to result in

an increase of dipterans. Carabid beetles and spiders

decreased in abundance and species richness follow-

ing fertiliser application (Luff and Rushton, 1989;

Rushton et al., 1989). King et al. (1985) found that the

relative abundance of native and introduced arthropod

species changes, with native species of Collembola

dominating native grassland, but introduced or

cosmopolitan species dominating in fertilised pastures

sown to exotic species.

Similarly, arthropods may respond to grazing

induced changes in habitats in a variety of ways.

For example, disturbance-tolerant beetles in the

families Scarabaeidae and Curculionidae (Kain,

1979; Bromham et al., 1999), and ants in the genera

Iridomyrmex and Rhytidoponera (Hutchinson and

King, 1980a; Lobry de Bruyn, 1993; Bromham et al.,

1999; Read and Andersen, 2000) were found to

increase in abundance following grazing, whereas,

other less tolerant groups declined (Morris, 1968;

King and Hutchinson, 1976, 1980, 1983; King et al.,

1976; Hutchinson and King, 1980a,b; Bromham et al.,

1999; Seymour and Dean, 1999).

This study of arthropod populations adds a further

dimension to an experiment that commenced in 1998,

in which different rates of superphosphate fertiliser

and other soil amendments were applied to a native

grassland in south-eastern Australia, with the aim of

improving grassland and domestic livestock produc-

tivity (Garden et al., 2003). The study found that

superphosphate application and increased grazing

resulted in a decline in native perennial grasses and an

increase in exotic annual grasses. Our study used the

same experimental plots and asked the question, do

arthropod assemblages within a native grassland show

changes in community composition in response to

increased fertiliser and grazing? The term grassland is

used rather than pasture to indicate that the experi-

mental area had not been sown to exotic species or

disturbed by cultivation or the use of herbicides.

2. Methods

The study site was located 22 km north of Yass on

the southern tablelands of New South Wales, Australia

(348400S 1488540E, altitude 670 m). Soils were

derived from Silurian tuffs, and varied from shallow

(<20 cm) Leptic Rudosol soils through bleached

mottled Chromosol and yellow Sodosol soil to deep

(>1.5 m) Hydrosol soils in low-slope areas. Soils were

low in P and S, and acidic in the surface layers

(pHCaCl2 4.1–4.9). Annual rainfall was 668 mm

I. Oliver et al. / Agriculture, Ecosystems and Environment 109 (2005) 323–334 325

evenly distributed throughout the year. Before treat-

ments the site was dominated by native C3 species,

mainly Austrodanthonia duttoniana (Cashmore) H.P.

Linder. Introduced annual species (Vulpia spp. and

Bromus spp.) were present at low densities, with some

Trifolium subterraneum L. and other annual clovers

(total species 64; native species 45% by number, 77%

by mass, Garden et al., 2003). No trees occurred in

study plots. The site had previously been grazed by

sheep at low-medium rates (3–5 sheep/ha) with

limited fertiliser (mainly P) application.

Experimental plots ranged from 0.5 to 0.83 ha with

two replicates of each of six treatments. Treatments

were randomly allocated to plots within blocks either

side of a central access lane, with replicate 1 (plots

1–6) generally being higher in the landscape and

having shallower soils. Treatments consisted of: a

control with no improvement; three levels of super-

phosphate (8.8% P, 11% S), i.e. low (62.5), moderate

(125) and high (250 kg ha�1); lime (250 kg ha�1

superphosphate + 2.5 t ha�1 lime); and sewage (5 t

ha�1 sewage ash). Superphosphate treatments were

applied in March 1998, 1999, May 2000, April 2001

and March 2002. Lime and sewage treatments were

applied in March 1998 only. Molybdenum was applied

as molybdenised superphosphate (0.02% Mo) to all

treatments (except sewage) in 1998 and 2002 at

25 g ha�1. Stocking rate was varied according to

available forage within treatments (Table 1), with the

aim of maintaining similar body weights across

treatments, and was adjusted by adding wethers from

a mob of similar animals grazed on similar unfertilised

pasture.

Table 1

Stocking rate (wethers/ha) as determined by available forage at the

experimental site in NSW

Year Month Control Low Moderate High Lime Sewage

1998 May 6 6 8 8 8 8

October 6 7.2 9.6 10 10 8

December 6 7.2 9.6 12 12 10

1999 October 7.2 8.4 11.2 14 14 12

2000 March 7.2 8.4 11.2 14 14 14

May 8.4 9.6 12.8 16 16 16

2001 May 8.4 10.8 14.4 16 20 16

Control: no fertiliser, low: 62.5, moderate: 125, high: 250 kg ha�1

superphosphate, lime: 250 kg ha�1 superphosphate + 2.5 t ha�1

lime, sewage: 5 t ha�1 sewage ash.

Soils were sampled before the experiment and

in autumn each year before fertiliser was applied.

From each plot 20 soil samples were collected 10 cm

deep along two separate 40 m transects and bulked

for analysis. They were dried, ground to pass a

2 mm sieve, and analysed by a commercial soil

testing laboratory for electrical conductivity, pHCaCl2 ,

PColwell, exchangeable cations, SKCl40 and organic

carbon, the latter two in autumn 2002 only.

Herbage mass (kg dry matter ha�1), ground cover

and botanical composition (percent of herbage mass)

were assessed every 6–7 weeks within 30 quadrats

(0.5 m � 0.5 m) along the same transects for soil

sampling using the BOTANAL technique (Andrew

and Lodge, 2003; Garden et al., 2003) and used to

determine the proportion of herbage mass contributed

by exotic species.

Sheep were removed from the plots in spring 2001

during arthropod sampling. Arthropods active on the

ground surface (epigaeic) were sampled using ten

250 ml pitfall traps (100 mm high, 67 mm internal

diameter), buried with the lip of the container flush

with the soil surface. Each contained 125 ml mono-

ethylene glycol to kill and preserve the trapped

arthropods. On November 6, 2001, two rows of pitfall

traps were installed in each plot 5 m either side of a

central 50 m transect. Traps were located at 5, 15, 25,

35, and 45 m along this transect and were active for 7

days after which they were removed, capped and

transported to the laboratory where the monoethylene

glycol was decanted off and replaced with 70%

ethanol.

Arthropods active within the soil (hypogaeic) were

recovered from soil cores taken within 50 cm of each

pitfall trap. Cores of 7.5 cm diameter, 5 cm deep were

taken through the grass, wrapped in aluminium foil

and transported to the laboratory for arthropod

extraction into 100% ethanol over 7 days using

Tullgren funnels (15 W globe 20 cm from the inverted

soil core). Five soil cores from each replicate were

taken on two occasions, the first when pitfall traps

were installed, the second when they were removed. A

random set of nine soil core samples was selected from

each replicate. Pitfall trap and soil core samples were

pooled per plot prior to identification and analysis.

Arthropods were identified to orders, morphospe-

cies (Oliver and Beattie, 1996a,b) or species, and

categorised into native or exotic taxa where possible.


Table 2

Abundance and richness of arthropods sampled by pitfall traps at the

experimental site in NSW

Abundance Richness

Formicidae 619 (0.11) 13 (0.11)

Voucher specimens were deposited with the Austra-

lian Museum, Sydney (Formicidae, Coleoptera and

Hemiptera), the Australian National Insect Collection,

Canberra (Acari) or the South Australian Museum,

Adelaide (Collembola).
Coleoptera 281 (0.05) 43 (0.38)
Collembola 1688 (0.30) 23 (0.20)

Acari 1744 (0.31) 28 (0.25)

Hemiptera 169 (0.03) 7 (0.06)a

Diptera 732 (0.13)b

Others 394 (0.07) –

Total 5627 114

a Hemiptera data were not analysed further due to low numbers of

species.b Diptera were not identified to species nor analysed further.

3. Analyses

Differences in total abundance and relative

abundance of exotic arthropods among treatments

were explored graphically and tested using one-way

anova. Changes in the soil and vegetation parameters

due to treatments were explored graphically and tested

using two-way anova (Gmav5, Underwood, 1995).

The ability of soil and vegetation parameters to

explain the variation in arthropod assemblages in

spring 2001 was tested using the direct gradient

analysis technique canonical correspondence analysis

(CCA) (CANOCO for Windows, ter Braak and

Smilauer, 2002). Correlated variables were first

identified by significant simple correlation coefficients

using data from final sampling periods and by

inspection of variance inflation factors within initial

CCAs (ter Braak and Prentice, 1988). Final CCAs

excluded correlated variables and were performed on

raw and transformed (x0.25) data. All default settings

were used for CCA other than requesting 9999 Monte

Carlo permutations to test for statistically significant

explanatory variables. Variables were tested indivi-

dually, and for their ability to explain significant

remaining variation in minimum models built by

forward selection. Tri-plots were produced using

CanoDraw (ter Braak and Smilauer, 2002).

4. Results

The pitfall traps sampled 5627 specimens from 114

arthropod species during the 7-day period in spring

2001 (Table 2), and the soil cores sampled 21,405

sarcoptiform mites from 15 species, and 5997

Collembola from 18 species. Collembola and Acari

were more abundant at higher superphosphate applica-

tion, Formicidae and Coleoptera in the control,

abundance under lime and sewage showing variable

trends among groups (Fig. 1). Average relative

abundance of Collembola and Acari of exotic origin

increased with increasing fertiliser application and

grazing (Fig. 2), statistically so for the hypogaeic Acari,

where the exotic Tyrophagus similis Volgin represented

96.7% of the sarcoptiform mites recovered.

Two-way anova revealed significant interaction

between treatment and time for pH (P < 0.001), and

phosphorus (P < 0.01), demonstrating that soil pH and

P had changed during the experiment and to varying

degrees among treatments (Fig. 3). Significant treat-

ment effects were also obtained for ground cover, exotic

biomass (Fig. 3) and S (one-way anova P < 0.01, S

treatment means were: control 3.5, low 3.9, moderate

5.9, high 7.8, lime 11.3, and sewage 3.4).

Simple correlations between February 2002 soil

data (d.f. = 10, P < 0.05 when r > 0.576) revealed a

number of highly correlated soil variables including:

EC, correlated with Al, Ca, K, Mg, Na, pH and S

(r = �0.810, 0.977, 0.669, 0.625, 0.586, 0.907, and

0.701, respectively); Al, correlated with Ca, K, P and

pH (r = �0.897, �0.653, �0.622, �0.951); and Ca,

correlated with K, pH and S (r = 0.658, 0.969, 0.643).

The three collinear variables EC, Al, and Ca were

therefore omitted from further analysis.

Initial CCAs (with EC, Al and Ca excluded)

revealed high variance inflation scores attributable to

S. Sulphur, which was positively correlated with K,

Na, pH and exotic biomass (r = 0.747, 0.693, 0.590,

and 0.588, respectively), was therefore omitted from

the final CCAs. All variance inflation factors for final

CCAs were less than 20. Final CCAs based on raw

data revealed that, when tested individually, ground

cover and exotic biomass explained significant

(P < 0.05) variation in hypogaeic Acari and hypo-


Fig. 1. Average total abundance of arthropods by treatment (with S.E.; Student–Newman–Keuls post-hoc multiple comparison tests).

gaeic Collembola assemblages (Table 3). However,

forward selection of variables found that exotic

biomass did not explain significant remaining varia-

tion in the models containing ground cover alone,

which accounted for 25% and 22% of the variation in

hypogaeic Acari and Collembola assemblages,

respectively. Exotic biomass was the single statisti-

cally significant explanatory variable for the epigaeic


Fig. 2. Average relative abundance of arthropods of exotic origin by treatment (with S.E.; Student–Newman–Keuls post-hoc multiple

comparison tests).

Acari and accounted for 22% of the variation. In

comparison, forward selection of variables found that

ground cover, pH and organic carbon together

accounted for 61% of the observed variation in the

epigaeic Collembola assemblage. A number of other

variables, including exotic biomass, were individually

significant but were not included in the minimum

model (Table 3). Organic carbon and ground cover

accounted for 45% of the observed variation in the

Formicidae assemblage, and soil P was the single

statistically significant explanatory variable for the

Coleoptera assemblage and accounted for 14% of the

variation. Results from CCAs based on transformed

(x0.25) abundance data were similar.

CCA tri-plots (Fig. 4) revealed separation of

control and low treatment plots from moderate and

high treatment plots, the former characterised by

lower ground cover and lower exotic plant biomass,

and by the native Collembola: Brachystomella

platensis Najt and Massoud (NU1), Proisotoma sp.

(N17), Subisotoma sp. (N9), and Corynephoria sp.

(N22) (Fig. 4a and c); and the native Acari:

Zygoribatula cycloporosa Lee (N3), Scheloribates

brevipodus Lee and Pajak (N19), Lanceoppia tasma-

nica Mahunka, (N1) Anellozetes sp. (N4), Rhagidia

sp. (N10), as well as the exotic species Petrobia latens

(Muller) (E4) (Fig. 4b and d). The higher treatment

plots were characterised by higher ground cover,

higher exotic plant biomass, the exotic Collembola:

Hemisotoma thermophila (Axelson) (E1), Hypogas-

trura vernalis (Carl) (E5), Entomobrya multifasciata

(Tullberg) (E2) and Isotomurus sp. (E3) (Fig. 4a and


Table 3

Variables that accounted for significant variation in arthropod assemblages when tested by CCA individually (ind) or as part of a minimum model

(mod)

Variable Acari Collembola Formicidae Coleoptera

Epigaeic Hypogaeic Epigaeic Hypogaeic Epigaeic Epigaeic

Ground cover ns mod, ind mod, ind mod, ind mod, ind ns

Exotic biomass mod, ind ind ind ind ns ns

Organic carbon ns ns mod ns mod, ind ns

pH ns ns mod, ind ns ns ns

Phosphorus ns ns ind ns ns mod, ind

Potassium ns ns ind ns ns ns

Variation explained (%)a 22 25 61 22 45 14

a Variation explained by minimum model calculated as the sum of all canonical eigenvalues divided by sum of all unconstrained eigenvalues

when the model included only those variables contained within the minimum model. Significance was tested by Monte Carlo permutation tests

with 9999 permutations, ns P > 0.05.

Fig. 3. Changes in some soil and vegetation parameters by treatment during the experiment (average of two plots per treatment are plotted). Plots

are identified by their treatments as: Control (&), Low ( ), Moderate ( ), High ( ), Lime ( ), Sewage (^). Two-way anova results for sources of

variation: treatment (tr), time (ti), and treatment x time interaction (txt), are *P < 0.05, **P < 0.01, ***P < 0.001. (a) pH, tr*** ti** txt***, (b)

phosphorus, tr** ti*** txt**, (c) ground cover, tr*, (d) exotic biomass, tr*** ti***.


Fig. 4. Tri-plots based on canonical correspondence analysis of Collembola and Acari raw abundance data. First (horizontal) and second

(vertical) canonical axes are plotted over the range �1 to +1. Vectors are shown as: dotted, when P > 0.05 for marginal test (variables tested

individually with 9999 permutations); solid when P < 0.05 for marginal test; and bold when P < 0.05 for conditional test (variables added to

minimum model by forward selection). Plots are identified by their treatments as: Control (&), Low ( ), Moderate ( ), High ( ), Lime ( ),

Sewage (^). Taxa are shown as alphanumeric couplets with E = exotic, N = native, NU = probable native taxa, and U = taxa of unknown origin.

All taxa were submitted to CCA but only those recorded at three or more plots are shown on the tri-plots. P-values from tests of significance of the

first and all canonical axes for each of the assemblages were: (a) 0.023, 0.028, (b) NS, 0.024, (c) 0.056, 0.033, (d) 0.000, 0.058, Formicidae NS,

NS, Coleoptera NS, NS, and were based on 9999 random permutations.


c); and the exotic Acari: T. similis (E1) and Halotydeus

destructor (Tucker) (E2) (Fig. 4b and d). The CCA tri-

plot for epigaeic Collembola (Fig. 4c) further

separated the moderate, high and lime treatment plots

based on the negatively correlated variables pH and

organic carbon. Moderate treatment plots, with lower

pH and higher organic carbon, were characterised by

native Collembola: Australotomurus sp. (N16), Lepi-

docyrtus sp. (N8) and Katianninae sp. (N1), with the

above exotic Collembola dominating the high and

lime treatments. The dominance of exotic arthropods

in the higher treatment plots supports the trends

observed in Figs. 1 and 2.

5. Discussion

Despite the site’s history of low grazing pressure,

limited fertiliser application, and its apparent good

condition, considerable impact on the biodiversity of

the grassland had already taken place. This was

revealed most notably by the hypogaeic Acari where

90.8% of the 1747 sarcoptiform mites sampled from

the control plots were the exotic species T. similis.

Exotic species, although less dominant, were also a

significant component of the epigaeic Acari and

Collembola sampled from the control plots.

How different are arthropod faunas of putatively

good condition grasslands compared with grasslands

which have not been managed for production?

Within the production landscapes of south-eastern

Australia very few locations have escaped continuous

grazing by domestic livestock. King and Hutchinson

(1983) found that grazing reduced the number of

hypogaeic Collembola with average abundance over

the duration of an experiment; 10,600, 7900 and

4350 individuals m�2 for ungrazed, lightly grazed

and heavily grazed treatments, respectively. These

results support a history of light grazing for the

study site (average abundance in control plots was

7520 individuals m�2), but also suggest that Collem-

bola abundance may have been reduced and composi-

tion altered as a result (King and Hutchinson, 1983).

The average mite density in the two control plots was

considerably higher than King and Hutchinson (1983)

numbers demonstrating that a history of light grazing

and occasional fertiliser application had led to

significant increases in hypogaeic Acari abundance,

the community composition being dominated by a

single exotic species.

After only 4 years of fertiliser treatment and

grazing on these plots, exotic arthropods became more

abundant and some native species were largely

restricted to the control or low input treatments.

The environmental gradients responsible for these

differences included ground cover, exotic biomass,

pH, phosphorus, organic carbon and potassium, with

the first four variables significantly affected by the

treatments. Further, the variables: electrical conduc-

tivity, aluminium, calcium and sulfur, were omitted

from the analyses due to colinearity. Gradients in these

omitted variables may have also been responsible for

the differences in assemblages observed among plots.

Plots that received higher input management were

therefore characterised by higher P, EC, Ca, and S, and

higher exotic biomass and ground cover, and lower

organic carbon and Al compared with the control and

low treatment plots. In addition, the lime treatment

resulted in a large increase in pH.

Considerable work has been completed overseas on

the impacts of changed soil pH on soil-active

arthropods, both in terms of soil acidification due to

fertilisers and acid rain, and soil neutralisation with

lime (Hagvar and Abrahamsen, 1980; Hagvar and

Amundsen, 1981; Hagvar and Kjøndal, 1981; Hagvar,

1984). These studies have also shown that artificial

changes of soil pH can result in large changes in the

abundance and composition of Acari and Collembola

communities. In fact, Huhta et al. (1983) showed that

several published effects of fertilisers on the soil fauna

may have actually been related to changes in soil pH

rather than direct effects of the chemicals themselves.

Altering the pH of soils will result in changes of the

arthropod fauna, whereas the implications of liming

for biodiversity conservation in Australian soils are

less clear. Where long-term fertiliser application and/

or the sowing of legumes has resulted in soil

acidification (King and Hutchinson, 1989; Lockwood

et al., 2003), increasing pH with lime may well have a

positive influence on a site’s native biota by returning

the soil to a more ‘‘natural’’ state. However, many

Australian soils are inherently acidic (Scott et al.,

2000), including those studied in this project. Liming

soils with naturally low pH may lead to local

extinction of endemic acidophilic species. Recom-

mendations for broad-scale application of lime to


naturally acidic soils, therefore, need to be treated with

caution if biodiversity loss is not to be exacerbated.

Considerable heterogeneity was revealed between

assemblages sampled from the two sewage plots. In all

cases, one sewage plot was located on the CCA tri-

plots near the ‘‘higher’’ input treatments, and the other

was positioned near the control and low input

treatments. We expect that these differences in

assemblages are a direct result of different starting

and finishing levels of phosphorus and pH in these two

plots. By the completion of the experiment in 2002,

phosphorus in one sewage plot had only increased

from 9.7 to 24 mg kg�1 (150%), and pH had

commenced at 4.6 and dropped to 4.5. In the second

sewage plot (located near the high-input plots on

the CCA tri-plots) phosphorus had increased by

nearly 450% from 6.4 to 35 mg kg�1, and pH had

commenced at 4.9 and dropped to 4.75. These

differences in starting and finishing soil conditions

were most likely related to differences in soil type

within the two plots. The former plot was on yellow

Chromosol and Leptic Rudosol soils, while the latter

was on yellow Sodosol and Hydrosol soils.

Despite these differences in starting conditions, it is

possible that the results for these two plots represent

either side of a biological threshold for arthropods.

That is, a 150% increase in phosphorus resulting from

the application of sewage ash appeared to have little

impact on arthropod biodiversity, whereas, a 450%

increase had a dramatic impact in line with high inputs

of superphosphate and lime. To the authors’ knowl-

edge no studies have been published on the impacts of

sewage ash on native species. However, several

investigations have explored the ecological impacts

of sewage sludge application but most have investi-

gated its use in, and effects on, forest plantations

(Costantini et al., 1995; Crohn, 1995; Loch et al.,

1995; Bramryd, 2001), but see Yeates (1995), Larsen

et al. (1996), Andres (1999) and Cole et al. (2001)

for reported impacts on arthropods. Further experi-

mentation of rates of application of sewage ash and

resultant impacts on arthropod biodiversity are clearly

warranted.

The sensitivity of native grasslands to domestic

grazing and fertiliser use was a critical finding of the

study. Our results revealed a significant historical

impact of low-input management and a further

decline in native arthropod biodiversity through

reduced abundance and/or local extinction of native

species and increased dominance of exotic species

with increased fertiliser use and grazing intensity.

These results are in accordance with Australian

studies conducted on the northern tablelands of New

South Wales (King and Hutchinson, 1983; King

et al., 1985). Consequently, our study, together with

those of others, suggests that improving native

grasslands with fertiliser in the naturally nutrient

poor landscapes of south-eastern Australia may not

be ecologically sustainable from the point of view of

biodiversity conservation (see Groves et al., 2003).

However, given the state of development and the

economic importance of production landscapes in

south-eastern Australia, we do not expect that our

study will initiate major landuse change. Our

findings do, however, support the critical need to

identify, de-stock, protect and restore a representa-

tive network of native grassland ecosystems within

this highly productive agricultural zone of Australia

(Eddy, 2002). Our results also suggest that monitor-

ing attempts to restore degraded grassland systems,

as well as monitoring the impacts of sustainable

grazing management practices, may well benefit

from the inclusion of an arthropod monitoring

component (Paoletti, 1999).

Acknowledgments

This project would not have been possible without

the existence of the experimental plots which were

established in 1997. We thank other members of the

project team responsible for the original experiment

including; Colin Langford, Peter Simpson, Colin

Shields and Tony Ciavarella, and the Murray-Darling

Basin Commission for funding the original experi-

ment. The authors also thank Sarah McGeoch, Rob Le

Lievre and Colin Shields for efficiently taking care of

the field component of this project, and Kithsiri

Dassanayake for exporting the botanical data from the

original experiment’s database. Mark Dangerfield,

Simon Ferrier, Dieter Hochuli, Warren Mason, Chris

Nadolny, Lance Wilke and Brian Wilson provided

constructive comments on earlier versions of this

paper. This project was funded by the NSW

Biodiversity Strategy and the then NSW Department

of Land and Water Conservation.


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Documents

Effects of fertiliser and grazing on the arthropod communities of a native grassland in south-eastern Australia