Effects of shading and mulch depth on the colonisation of habitat patches by of rainforest soil and litter

Author Nakamura, Akihiro, Catterall, Carla P, Burwell, Chris J, Kitching, Roger L, House, Alan PN

Published 2009

Journal Title Conservation and Diversity

DOI https://doi.org/10.1111/j.1752-4598.2009.00056.x

Copyright Statement © 2009 the Royal Entomological Society and the Authors. This is the author-manuscript version of this paper. Reproduced in accordance with the copyright policy of the publisher. Published by Blackwell Publishing Ltd. The definitive version is available at www.blackwell-synergy.com

Downloaded from http://hdl.handle.net/10072/30633

Griffith Research Online https://research-repository.griffith.edu.au 1 Effects of shading and mulch depth on the colonisation of habitat

2 patches by arthropods of rainforest soil and litter

3

4 By Akihiro Nakamura1*, Carla P. Catterall1, Chris J. Burwell1,2, Roger L. Kitching1,

5 and Alan P. N. House3

6

7 1 Centre for Innovative Conservation Strategies and Griffith School of Environment, Griffith University,

8 170 Kessels Road, Nathan, Queensland 4111,

9 2Queensland Museum, Cnr Grey and Melbourne Streets, South Brisbane, Queensland 4101, Australia

10 3CSIRO Sustainable Ecosystems, 306 Carmody Road, St Lucia, Queensland 4067, Australia

11

12 Manuscript for Insect Conservation and Diversity

13

14 Word count: 4698 (Introduction, Methods, Results, Discussion, Acknowledgements)

15

16 *Corresponding author

17 Corresponding author’s current address: Queensland Museum, Cnr Grey and Melbourne Streets, South

18 Brisbane, Queensland 4101, Australia

19 Telephone: +61 (0)7 3840 7703

20 Fax: +61 (0)7 3735 7014

21 E-mail: [email protected]

22

23 RUNNING TITLE: colonisation in forest restoration

1 24 ABSTRACT

25 1. Development of foliage cover and a layer of leaf litter are two factors considered

26 important for the successful recolonisation of soil and litter arthropods during the

27 early stages of rainforest restoration; however, this needs to be tested explicitly.

28 2. We employed a manipulative field experiment to assess the effects of shading and

29 litter depth on colonisation patterns of soil and litter arthropods in created habitat

30 patches at five replicated sites within pasture adjacent to rainforest remnants on the

31 Maleny plateau of subtropical eastern Australia.

32 3. Habitat patches were created by adding sterilised mulch at two depths (shallow 3-5

33 cm, deep 10-15 cm) under three levels of shading (none, 50%, 90%). Responses of

34 arthropods to treatments were analysed at two levels of taxonomic resolution:

35 ‘ordinal-sorted arthropods’ (all arthropods sorted to order/class) and species

36 (: Formicidae).

37 4. Shading, at both 50% and 90%, encouraged colonisation by arthropods

38 characteristic of rainforest. Colonisation by pasture-associated arthropods declined

39 progressively with increased shading. Effects of mulch depth were significant only

40 for rainforest-associated ant species, which responded positively to shallow mulch

41 within shaded plots.

42 5. The results confirm that canopy cover is indeed one of the primary attributes

43 influencing colonisation patterns of arthropods in restored vegetation. More

44 widely-spaced plantings may facilitate some colonisation by rainforest arthropods.

45 However, in order to suppress invasion by pasture-associated arthropods, it may be

46 necessary to establish a fully closed canopy.

2 47 KEYWORDS

48 , bio-indicators, epigaeic invertebrates, reforestation

3 49 INTRODUCTION

50 Australian tropical and subtropical rainforests are some of the few worldwide in

51 which deforestation has all but ceased, and increasing effort is being invested in

52 rainforest restoration, often with the aim of recovering biota characteristic of

53 pre-disturbed habitats (Catterall & Harrison, 2006). The last decade has seen a growing

54 number of studies of tropical and subtropical rainforest restoration, investigating

55 recolonisation by various faunal groups including arthropods (see Nakamura, 2007).

56 Studies have assessed a range of factors that may influence recolonisation patterns of

57 rainforest fauna, including spatio-temporal aspects of the restoration (e.g. isolation, age),

58 plant species composition and structural complexity, canopy cover and litter quality and

59 quantity.

60 Among these factors, canopy closure has been considered a key component

61 facilitating the development of fauna, especially during early stages of rainforest

62 restoration (Catterall et al., 2008; Grimbacher et al., 2007; Jansen, 1997; Kanowski et

63 al., 2006; Nakamura et al., 2003). A closed canopy provides a shaded forest floor which

64 is associated with increased moisture content and reduced temperature fluctuations in

65 soil and litter microhabitats (Neumann, 1973). These factors are significant

66 determinants of the diversity and abundance of soil and litter arthropods (Chikoski et al.,

67 2006; Entling et al., 2007).

68 The level of shading achieved during rainforest restoration, therefore, has important

69 implications for the development of rainforest-like arthropod assemblages, as different

70 reforestation techniques achieve different degrees of canopy cover. Timber plantations

71 have been advocated to catalyse rainforest reforestation because they also yield

4 72 economic returns (Lugo, 1997). However, the density of trees in plantations is generally

73 sparse (400-1000 stems/ha) compared with ecological restoration where a diverse array

74 of rainforest plants are planted at densities of several thousand stems/ha (Catterall &

75 Harrison, 2006). In tropical and subtropical regions, timber plantations achieved much

76 lower levels of canopy cover (25-60%) than ecological restoration plantings (75-80%)

77 and intact rainforest (93-95%), at least during the earlier stages of reforestation (5-22

78 years since establishment) (Kanowski et al., 2003). However, increasing the amount of

79 litter in plantations may help offset a more open canopy, by providing better insulation

80 against temperature and moisture extremes, and more resources for colonising soil and

81 litter arthropods (Greenslade & Majer, 1993; Koivula et al., 1999; Majer et al., 1984;

82 Nakamura et al., 2003). This may be achieved through the addition of a layer of organic

83 mulch (such as woodchips or hay) during the early stages of restoration. Mulch is often

84 used in ecological plantings to improve the survival of tree seedlings by suppressing

85 grass and exotic herbs and conserving moisture. However, we do not know if mulching

86 also benefits soil and litter arthropods, as the effects of shading and litter depth on

87 colonisation patterns have not been systematically studied in restored rainforests.

88 We investigated the effects of shading and mulch depth on the development of

89 assemblages of soil and litter arthropods in experimentally-created habitat patches

90 within a rainforest landscape now dominated by pasture. This experimental approach

91 enabled us to test systematically the focal factors without interactions with extraneous

92 factors, such as plant species and litter composition, habitat area and proximity to the

93 nearest rainforest, which are inherently variable in studies of actual restoration programs.

94 We test the hypothesis that the abundance and diversity of rainforest-associated

95 arthropods in restored patches will increase with increased shading and that an opposite

5 96 pattern will occur for pasture-associated arthropods. Further, we test whether increased

97 mulch depth compensates for reduced shading.

98 METHODS

99 Study area

100 The study was undertaken on the Maleny plateau, in the Sunshine Coast hinterland

101 of eastern Australia (26° 40’- 50’ S, 152° 45’- 53’ E, elevation 350 to 530 m). Mean

102 daily maximum and minimum temperatures in mid-summer (January) are 28.9° and

103 18.8°C respectively, and 19.5° and 7.1°C in mid-winter (July). Average annual rainfall

104 in the region is 1851 mm, with most falling between December and April. Total

105 precipitation during the study period (1437 mm between August 2003 and April 2004)

106 was below average for those months (1633 mm).

107 Five replicated experimental sites, each comprising an area of pasture abutting a

108 fenced rainforest remnant, were dispersed across a study region of approximately 170

109 km2. Remnants varied from 1.15 ha at one site to over 10 ha at other sites, and were

110 either old regrowth (age of ca.100 years) or had been selectively logged until recently.

111 Further details of study sites are provided in Nakamura et al. (2007).

112 Experimental design

113 At each site, we established a series of 3 m x 3 m experimental plots that simulated

114 conditions experienced by soil and litter arthropods within areas of rainforest restoration.

115 All plots were situated in pasture within two metres of a rainforest remnant, so that the

116 results were not confounded by distance effects on colonisation (see Nakamura et al.,

117 2008b). Plots were at least 5 m apart (Fig 1).

6 118 Plots were first sprayed with approximately 400-600 ml of broad spectrum herbicide

119 (Roundup® Biactive™, 7.2 g/L Glyphosate), in line with actual restoration procedures

120 conducted in the region (Big Scrub Rainforest Landcare Group, 2005; Goosem &

121 Tucker, 1995). A companion study found no short- or long-term impacts of the

122 herbicide on soil and litter arthropods inhabiting rainforest litter (Nakamura et al.,

123 2008a). Plots were then fenced with barbed wire to a height of 1.2m to exclude stock.

124 Three weeks after herbicide application, all visible vegetation (dead and alive) was

125 removed by hand.

126 Plots were either unshaded or covered with Sarlon® shadecloth rated at either 50%

127 or 90% protection from insolation. Shadecloth was placed over the top of the plot and

128 20-40 cm down each side and cut in 15 – 20 places with a slit length of 10 – 15 cm to

129 permit sunflecks and throughfall of rain. No live plants were planted within

130 experimental plots as this was pragmatically difficult and would confound effects of the

131 focal factors.

132 A mulch of woodchip and leaf material was placed in either a ‘shallow’ (3-5 cm) or

133 ‘deep’ (10-15 cm) layer in a square quadrat (2.5 m x 2.5 m) within each plot. The

134 mulched area was bordered by wire netting (40 cm high, hexagonal mesh size of 1.5 cm

135 (maximum height) x 2 cm (maximum width)) to minimise loss of mulch due to wind or

136 disturbance by larger wildlife. Mulch was derived from vegetation lopped from around

137 powerlines in various locations within about 150 km of the study region, and comprised

138 a mix of foliage and wood derived from rainforest and eucalypt species. Mulch was

139 steam-sterilised for 100 minutes before application to minimise the introduction of

140 exotic species and to create ‘empty’ habitat patches. Sterilised mulch was stored

7 141 beneath plastic sheets to minimise any casual arthropod colonisation and distributed to

142 plots within seven days after steam-treatment.

143 Seven plots were constructed at each of the five sites. Six plots were experimental

144 treatments, with three levels of shading (0%, 50%, 90%) and two levels of mulch depth

145 (shallow, deep). The seventh was a control plot which received herbicide treatment and

146 vegetation removal but no shadecloth or mulch (Fig 1). Construction of the field

147 experiment took place between May and August 2003.

148 Sampling methodology

149 Arthropods

150 Pitfall trapping and litter extraction was carried out between 9 April and 7 May

151 2004, approximately nine months after the plots were established. Four pitfall traps

152 were installed on the diagonal lines of each plot, approximately 80 cm from the centre.

153 Each trap was a 120 ml plastic vial (44 mm in diameter), buried in the ground with the

154 lip flush with the surface. Vials were filled with 70 to 80 ml of 70% ethanol with a

155 small amount of glycerol. Pitfall traps were operated for five days. Before data analyses,

156 samples from the four pitfall traps were pooled. Litter samples were taken immediately

157 before pitfall trapping. One litre of litter and surface soil (approx. 20% surface soil and

158 80% litter by volume to a depth of 1 to 2 cm) was collected in small amounts evenly

159 over the entire plot area. Samples were placed in Tullgren funnels within 12 hours of

160 sampling, and extracted for 4.5 days using 40 watt clear light bulbs.

161 During sampling, care was taken to avoid cross-contamination among the

162 experimental plots. All footwear was covered with thick polythene film and researchers

163 were thoroughly brush-cleaned before and after visiting each plot.

8 164 Identification of arthropods was to order except (a) Hymenoptera which were split

165 into Formicidae and ‘others’; and (b) myriapods, which were sorted to class. Acari and

166 Collembola were not sorted due to their high abundance and ubiquitous occurrence

167 regardless of the experimental treatments. (Hymenoptera: Formicidae) were

168 selected as a target taxon, and sorted to species. Where possible, ants were identified as

169 described species by CJB, using published taxonomic literature, otherwise they were

170 assigned species codes. Voucher specimens are deposited at Griffith School of

171 Environment, Griffith University.

172 Soil moisture content and temperature

173 During arthropod sampling (between 15 April and 7 May 2004), soil moisture

174 content was measured by hand-collecting approximately 50 cm3 of topsoil (up to 2 – 3

175 cm in depth) from each experimental plot at the five sites as well as their adjacent

176 rainforest and pasture areas. Small amounts of topsoil were collected evenly over the

177 plot area, and within 2.5 m x 2.5 m quadrats established within rainforest and pasture at

178 each site. Each soil sample was kept in an airtight plastic bag, and weighed before and

179 after it was oven dried for 24 hours at 105° C. Ground temperature was recorded at 30

180 minute intervals for 5.5 days (14 to 20 April 2004) using temperature loggers (HOBO®

181 Temperature Data Logger, Onset Computer Corporation, MA), deployed at the

182 experimental plots and surrounding rainforest and pasture areas in one site only. The

183 temperature sensor was placed on the ground surface (beneath the mulch, except in the

184 un-mulched control plot), in the centre of each plot.

185 Data processing

186 Data were analysed in three different sets: (i) arthropods sorted to order/class

9 187 (referred to as ‘ordinal-sorted arthropods’ hereafter), (ii) ant species and (iii) ant

188 functional groups (Andersen et al., 2003). Each dataset was further divided into two

189 subsets comprising data sampled using pitfall traps and litter extraction. Abundances of

190 ordinal-sorted arthropods were log transformed before analysis. Abundances of ant

191 species were scored on a seven-point ordinal scale following Andersen et al. (2003): 1 =

192 1, 2 = 2-5, 3 = 6-20, 4 = 21-50, 5 = 51–100, 6 = 101-1000, 7 = >1000 individuals.

193 Abundances within ant functional groups were expressed as proportions of all ants at

194 each plot, and arcsine-transformed for analysis.

195 In addition to data from the present study, we incorporated data from a preceding

196 survey (Nakamura et al., 2007), which provided baseline information on the difference

197 between the arthropod assemblages of rainforest and pasture habitats in the study region.

198 That survey was carried out in the same location and in a similar season the previous

199 year (8 January to 6 May 2003). Arthropods were collected from three sampling points

200 at each of 24 sites (12 in rainforest remnants and 12 in pasture) across the Maleny

201 region, including the five used for the present study. Although the baseline arthropod

202 sampling was carried out over a slightly larger area than in the present experimental

203 study (each sampling point comprising a circular area of 3 m radius), sampling and

204 sorting protocols were otherwise identical, so that direct comparison was possible.

205 Baseline survey data were used to identify indicator taxa for either rainforest or

206 pasture habitats, based on the Indicator Value protocol (Dufrene & Legendre, 1997).

207 Rainforest/pasture indicators were classed as either ‘specialist’ (found exclusively in

208 either rainforest or pasture) or ‘increaser’ (found in both habitat types but significantly

209 more abundant in one). Taxa that did not have significant habitat preferences were

10 210 classed as ‘generalist’ (see Nakamura et al., 2007 for more details).

211 Many individual habitat indicator taxa were of limited usefulness due to their patchy

212 distributions (Nakamura et al., 2007). To develop a more robust indicator statistic,

213 additional ‘composite rainforest/pasture indices’ were generated for only two of the

214 selected data sets (viz. ordinal-sorted arthropods, ant species). To calculate composite

215 indices of ordinal-sorted arthropods, abundance values of each of the indicator taxa (as

216 defined by the baseline survey) were first individually range-standardised to give values

217 between 0 and 1 for each taxon at each site (site-specific abundance minus minimum

218 abundance across all sites / maximum minus minimum abundance across all sites). This

219 was done to remove the effects of large differences in taxon-specific abundance. The

220 range-standardisation procedure was not carried out for ant species, as most indicator

221 species had similar abundance scores (most from 0 to 4, with a maximum of 6). The

222 range-standardised abundance (ordinal-sorted arthropods) or abundance scores (ant

223 species) of rainforest or pasture indicator taxa were then summed to give composite

224 indices of rainforest or pasture habitat at each site. Composite indices provided a single

225 value quantifying the extent to which a site resembled rainforest or pasture. Composite

226 indices were calculated separately for ordinal-sorted arthropods and ant species

227 collected by either pitfall traps or litter extraction and were calculated only if two or

228 more of the component indicator taxa/species were present.

229 Data analysis

230 Two-factor crossed ANOVAs with randomised complete block design were carried

231 out, using SPSS (Rel.13.0) statistical software (SPSS Inc., 2004) to evaluate the

232 responses of variables (total abundances, taxon richness, individual arthropod

11 233 abundances, composite rainforest/pasture indices, soil moisture contents) to the

234 experimental treatments. Factors tested were shading (0%, 50%, 90%), mulch depth

235 (shallow, deep) and their interaction. Between-site variation (blocks) was included as a

236 random factor. Analyses of variance were carried out on the abundance of an individual

237 taxon only if it occurred in at least four of the total experimental plots used for the

238 analyses (N = 30). To enable direct comparison with rainforest and pasture reference

239 sites, we also present baseline survey data from the same five sites (one randomly

240 selected sampling point from the three at a site).

241 Nonparametric multivariate analyses of variance (MANOVA) were carried out with

242 PERMANOVA software (Anderson, 2005) to test for responses of arthropod

243 assemblages to the experimental treatments. Factors tested were the same as in the

244 univariate analyses of variance. Between-site variation (blocks) was accounted for by

245 including sites in the program as covariates, in a manner specified by M. Anderson

246 (personal communication).

247

248 RESULTS

249 Arthropod assemblages and their response to shading and mulch

250 Overall abundances

251 A total of 8839 arthropods was sampled from the experiment, the majority from

252 pitfall traps (7162 individuals). Among 28 ordinal-sorted taxa identified, ants were the

253 most abundant with 3633 individuals (2897 from pitfall traps), followed by Coleoptera

254 with 1846 and Araneae with 582 individuals. Of the 52 ant species identified, 26 were

12 255 rare, occurring at less than four plots.

256 A significant effect of shading was found for the total abundances of pitfall-trapped

257 ants (ANOVA for the effect of shading and mulch depth: P = 0.019, P = 0.272

258 respectively, with interaction P = 0.558); a post-hoc LSD test showed that abundances

259 were greater in 0% (mean = 106.6) and 50% shading (95.3) than in 90% shading (44.9).

260 Neither the abundance nor taxon richness of ordinal-sorted arthropods, nor the species

261 richness of ants responded significantly to the shading or mulch depth treatments

262 (results not shown).

263 Ordinal-sorted arthropods

264 Among pitfall-trapped ordinal-sorted arthropods, two taxa were rainforest

265 ‘specialists’ (Archaeognatha, Opilionida), as defined by Nakamura et al. (2007); nine

266 rainforest ‘increasers’ (Blattodea, Coleoptera, Dermaptera, Diplopoda, Diplura,

267 Heteroptera, Isopoda, Pseudoscorpionida, Psocoptera); and three pasture ‘increasers’

268 (Araneae, Homoptera, Orthoptera). Among litter-extracted arthropods, there were 14

269 rainforest ‘increasers’ (Amphipoda, Blattodea, Chilopoda, Coleoptera, Dermaptera,

270 Diplopoda, Diplura, Formicidae, Heteroptera, Isopoda, ‘other Hymenoptera’, Pauropoda,

271 Pseudoscorpionida, Symphyla) and a single pasture ‘increaser’ (Orthoptera).

272 Despite the large number of indicator taxa, few showed statistically significant

273 responses to shading and litter depth (Table 1). A number of ‘generalists’ significantly

274 responsed to shading, mostly showing elevated abundances in plots at 0% and/or 50%

275 shading, while abundances at 90% were lower.

276 Despite the lack of responses from individual indicator taxa, the composite index of

277 rainforest ‘increasers’ based on pitfall-trapped ordinal-sorted arthropods responded

13 278 positively to an increase in shading from 0% to 50% (Fig. 2a, Table 2). No experimental

279 treatments affected the composite index of litter-extracted rainforest ‘increasers’ (Fig.

280 2b, Table 2). Shading also had a significant negative effect on the composite index of

281 pasture ‘increasers’: abundances of pasture-associated arthropods were lower in the

282 plots under 50% and 90% shading than in plots without shading, with no significant

283 interaction between shading and mulch depth (Fig. 2c, Table 2). Composite habitat

284 indices were not calculated for any habitat ‘specialists’ due to very rare occurrences

285 (presence in less than four plots) of their component taxa.

286 Multivariate analyses using PERMANOVA showed statistically significant effects

287 of shading on the composition of pitfall-trapped ordinal-sorted arthropod assemblages

288 (Table 2). A post-hoc permutation test showed that the coarse taxonomic composition of

289 arthropod assemblages under 0% shading differed significantly from those under both

290 50% and 90% shading. Shading and litter depth treatments did not have a significant

291 influence on the taxonomic composition of litter-extracted ordinal-sorted arthropods.

292 Ant species

293 Among pitfall-trapped ants, there were six rainforest ‘specialists’, as defined by

294 Nakamura et al. (2007) (Anonychomyrma QM3, Leptomyrmex erythrocephalus

295 rufithorax, Monomorium tambourinense, Pheidole QM1, Pheidole QM2, Pheidole sp.2),

296 two rainforest ‘increasers’ (Notoncus capitatus, Rhytidoponera chalybaea), three

297 pasture ‘specialists’ (Cardiocondyla nuda, Pheidole QM3, Rhytidoponera metallica),

298 and one pasture ‘increaser’ (Carebara QM1). Among litter-extracted ants, a single

299 species of each group was found: a rainforest ‘specialist’ (Carebara QM2), a rainforest

300 ‘increaser’ (Hypoponera sp.1), a pasture ‘specialist’ (Pheidole QM3), and a pasture

14 301 ‘increaser’ (Carebara QM1).

302 As the occurrences of most ant indicators were patchy, only eight satisfied the

303 frequency requirement for statistical analysis (presence in at least four of the 30 plots).

304 Of the four rainforest indicators tested, Hypoponera sp.1 (litter-extracted rainforest

305 ‘increaser’) responded significantly to the experimental treatments (Table 3),

306 progressively increasing in abundance with increased shading.

307 Within pitfall-trapped ants, the composite index value for rainforest ‘specialists’ was

308 greater in plots with shallow than deep mulch (Fig. 3a, Table 4). No experimental

309 treatments influenced the composite index of rainforest ‘increasers’ significantly (Fig.

310 3b, Table 4). Levels of the composite index of pasture ‘specialists’ were significantly

311 lower in plots with 90% shading compared with those with 0% shading (Fig. 3c, Table

312 4). Composite habitat indices were not calculated for litter-extracted ants, as only one

313 component species was identified for each group of habitat indicators.

314 Multivariate analysis showed statistically significant effects of shading on species

315 composition of pitfall-trapped ant assemblages (Table 4). The response was similar to

316 that observed for ordinal-sorted arthropods: assemblages of pitfall-trapped ant species in

317 plots under 0% shading were different from those under 90% shading, and assemblages

318 under 50% shading were intermediate.

319 No ant functional groups responded significantly to the experimental treatments.

320 The strongest response within ant functional groups was that pitfall-trapped ‘cryptic

321 species’ showed a non-significant trend to increase in relative abundance with increased

322 mulch depth (ANOVA for the effect of shading and mulch depth: P = 0.226, P = 0.083

323 respectively; interaction P = 0.520).

15 324 Soil moisture content and temperature

325 Mean soil moisture content was higher in pasture (at least 100 m away from the

326 forest edge) than in rainforest (Fig. 4). Compared with control plots (no mulch or

327 shading), a relatively high soil moisture content was maintained by all experimental

328 plots regardless of differences in shading and mulch depth; however, none were as

329 moist as the pasture or rainforest reference sites. No significant effects of shading or

330 mulch depth were found on soil moisture content across the experimental treatments

331 (two-factor ANOVA for the effect of shading and mulch depth: P = 0.885, P = 0.158

332 respectively; interaction P = 0.670), whereas a single factor ANOVA found significant

333 differences among pasture, rainforest, no mulch (control) and the combined

334 experimental treatments (P < 0.001), with pairwise tests showing that all were different.

335 Temperatures recorded in rainforest were lower on average than those in pasture,

336 and the coefficient of variation of half-hourly temperatures over five days in rainforest

337 was about half that of pasture (Fig. 5a). The provision of mulch in the experimental

338 plots suppressed extreme temperature fluctuations (compare the control plot in Fig. 5a

339 with mulched, unshaded plots in Fig. 5b). The presence of shading further reduced

340 average temperatures and their coefficients of variation (Fig. 5b).

341 DISCUSSION

342 Responses of arthropods to shading and litter depth

343 Previous studies of soil and litter fauna development in revegetated sites have

344 reported an initial colonisation by species tolerant of harsh environmental conditions

345 (e.g. Andersen, 1993; Dunger et al., 2001; Fox & Fox, 1982; van Aarde et al., 1996). As

16 346 the restored habitat developed, these species were gradually or abruptly replaced by

347 others characteristic of undisturbed habitats. In the context of rainforest restoration, our

348 results suggest that successional patterns of this type could occur as a function of

349 increased shading alone. The effects of shading shown here are consistent with the

350 findings of other studies emphasising the importance of structural attributes, including

351 canopy cover, for the organisation of soil and litter arthropod assemblages (e.g.

352 Grimbacher et al., 2007; Holmes et al., 1993; Lassau & Hochuli, 2004; Proctor et al.,

353 2003; Watts & Gibbs, 2002). Exceptions to this pattern include some groups of

354 arthropods that are linked strongly with biological traits of live plant species (e.g.

355 herbivores, which show strong host-plant affinities, Hunter & Price, 1992; Wardle,

356 2006).

357 The observed patterns of arthropod colonisation may be due, at least in part, to

358 ameliorated temperature regimes in shaded plots. Temperature tolerance is important in

359 influencing the distribution of ground-dwelling arthropods (Addo-Bediako et al., 2000;

360 Pearson & Lederhouse, 1987), and a number of restoration studies have shown that

361 arthropods characteristic of rainforest prefer cooler microclimatic conditions

362 (Grimbacher et al., 2006; King et al., 1998). In contrast, soil moisture content did not

363 explain colonisation patterns of arthropod assemblages (as it did not vary significantly

364 among the experimental plots), even though small arthropods could arguably be more

365 sensitive to reduced moisture levels (Levings & Windsor, 1984; Shure & Phillips, 1991).

366 Had we conducted sampling in winter (typically cool and dry), the patterns and role of

367 soil moisture may have been different, although arthropod activity and abundance

368 would have been lower.

17 369 In addition to the effects of microclimatic conditions, growth of herbaceous

370 vegetation may have affected arthropod colonisation patterns, particularly those

371 characteristic of pastures. Unshaded plots and some of the plots with 50% shade showed

372 increased levels of colonisation by pasture-associated taxa (Fig 2c). In these types of

373 plot there was visible regrowth of herbaceous pasture plants, which potentially provided

374 food and habitat for pasture-associated herbivorous arthropods, such as Homoptera and

375 Orthoptera. Colonisation patterns of pasture ant species may have also been influenced

376 by the supply of food resources (e.g. seeds from pasture, honeydew from Homoptera)

377 associated with the growth of pasture plants.

378 In contrast to the strong effects of shading, our results suggest that the amount of

379 litter may not be a strong determinant of arthropod assemblages in the context of

380 rainforest restoration. Our results were consistent with the findings of other restoration

381 studies of soil and litter arthropods colonising revegetated landscapes in various habitats

382 (viz. sclerophyllous and temperate forest, shrubland, grassland, dune forest, heathland

383 and rainforest), mainly from Australasia, Europe, North America and South Africa (53

384 studies reviewed by Nakamura (2007)). Using empirical and anecdotal evidence, these

385 studies evaluated a large number of biotic and abiotic factors that potentially influence

386 the colonisation of arthropod groups, including ants, beetles and spiders.. The effects of

387 differing levels of canopy cover and litter have been well studied, investigated by 14

388 and 21 studies respectively. While significant or potential impacts of shading were

389 reported by all of the 14 studies, this was not the case for the effect of litter quantity.

390 Seven of the 21 studies (including studies conducted in rainforest reforestation of

391 formerly cleared landscapes, Jansen, 1997; King et al., 1998), found no apparent

392 responses in the rate of arthropod colonisation to different amounts of forest litter.

18 393 Although rainforest-like arthropod assemblages may require the presence of at least

394 some litter similar to that typically found on the rainforest floor (ca. 3 cm, see King et

395 al., 1998; Nakamura et al., 2003), our results indicate that further addition of mulch

396 does not benefit their colonisation.

397 It could be argued that the observed results may have been different had we

398 incorporated other arthropod groups (e.g. spiders, beetles) into species-level analyses

399 (Wassenaar et al., 2005). Furthermore, the use of higher taxonomic levels may have

400 obscured significant responses, as individual species within an order may have

401 responded in different manners. However, our results were consistent with other

402 restoration studies incorporating diverse groups of soil and litter arthropods (Nakamura

403 2007, see above), suggesting that the fundamental patterns of arthropod colonisation

404 would not have differed regardless of the arthropod groups investigated.

405

406 Effects of the experimental context

407 Most restoration studies to date have employed a post-hoc empirical approach to

408 investigate the effects of factors considered important for the development of colonising

409 fauna (Michener, 1997). The ecological effects of the factors under investigation are

410 therefore difficult to elucidate, due to the presence of extraneous factors (Block et al.,

411 2001; Catterall et al., 2004). This problem is further exacerbated by the fact that

412 restoration projects are generally carried out on a site-specific basis with no spatial

413 replication, limiting inference from the data (Block et al., 2001). This study provided an

414 opportunity to test systematically the factors of interest since the experimental approach

415 allowed for the construction of replicated units in which focal factors (i.e. shading and

19 416 litter depth) were manipulated, while extraneous factors were controlled.

417 There were, however, a number of constraints associated with the experimental

418 design, which potentially limited colonisation of the constructed plots by

419 rainforest-dependent arthropods. First, experimental plots lacked some of the habitat

420 components of reforested sites, namely live plants that supply freshly shed foliage and

421 woody debris, both of which may be important for the colonisation and persistence of

422 rainforest-dependent arthropods (Andrew et al., 2000; Majer et al., 1984). Second, the

423 mulch used in the experiment had been sterilised with steam, which may have killed

424 potential food resources (e.g. prey micro-invertebrates, bacteria, fungi), and may have

425 altered the chemical composition of the mulch, making it more or less favourable to

426 arthropods. Third, the spatial and temporal scale of the experiment may have been

427 insufficient for successful colonisation, although the location of plots adjacent to the

428 forest edge maximised the probability of rainforest-associated taxa moving into the

429 plots (Nakamura et al., 2008b). These limitations may be reflected by the low

430 colonisation rates of litter-associated rainforest ant species (e.g. Mayriella abstinens

431 complex, Strumigenys harpya, Discothyrea and Lordomyrma spp., see Nakamura et al.

432 2007), which were either very low in abundance or absent from the experimental plots.

433 Nevertheless, a diverse array of arthropods, including rainforest-dependent taxa (albeit

434 not as diverse as those commonly found in rainforest), did colonise the experimental

435 plots and their assemblage composition responded differentially to the experimental

436 treatments.

437 Implications for practice

438 In order to maximise rainforest biodiversity values (the occurrence of biota and

20 439 ecological process typical of intact rainforest; Catterall et al., 2004), restored habitat

440 patches need to facilitate colonisation by fauna characteristic of rainforests, while

441 inhibiting (re-)invasion by taxa characteristic of the matrix habitat (i.e. pasture). Our

442 results show that rainforest restoration using lower density plantings, such as timber

443 plantations, may facilitate colonisation by rainforest soil and litter arthropods even

444 though canopy cover is not developed as rapidly, or to the same extent, as in

445 ecologically-designed restoration plantings. However, the establishment of a fully

446 closed canopy (90%) appeared to inhibit invasion by arthropods characteristic of the

447 matrix habitat most effectively. Using deeper mulch did not create more suitable

448 conditions for rainforest arthropods or offset the deleterious effects of less shade.

449 ACKNOWLEDGEMENTS

450 This study would not have been possible without the support of the Maleny

451 landholders who generously lent parts of their pastures for the construction of the

452 experimental plots. We are also grateful to Alan Andersen, Marti Anderson, Harry

453 Hines, John Kanowski, Scott Piper, Heather Proctor, and Cas Vanderwoude for

454 assistance and advice. Thanks also to Barung Landcare and our volunteer workers for

455 field and laboratory assistance. Steaming facilities were generously provided by the

456 Queensland Department of Primary Industries Fire Ant Research Centre. This research

457 was funded by the Rainforest Cooperative Research Centre and the Queensland

458 Government’s Growing the Smart State program. Akihiro Nakamura was supported by

459 a Griffith University Postgraduate Research Scholarship.

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24 Table 1. Effects of shading and mulch depth on abundances of ordinal-sorted arthropod taxa: results only for taxa where the main effects of ANOVA P < 0.05. Between-site effects are also shown. ‘Difference’ shows the results of LSD tests (levels with different letters are significantly different; A smaller, B larger, P < 0.05). Degrees of freedom (df) for shading, mulch depth, interaction and site are 2, 1, 2, and 4 respectively. P value

Indicator category Freq† Shading (S) Depth (D) S x D Site Difference

Pitfall traps

Formicidae ‘Generalist’ 30 0.019 0.272 0.558 0.441 0%(B) 50%(B) 90%(A)

Other Hymenoptera ‘Generalist’ 29 0.035 0.911 0.468 0.001 0%(A) 50%(B) 90%(A)

Pauropoda ‘Generalist’ 9 0.041 0.561 0.165 <0.001 0%(B) 50%(A) 90%(A)

Thysanoptera ‘Generalist’ 17 0.009 0.677 0.915 0.112 0%(B) 50%(A) 90%(A)

Litter extraction

Thysanoptera ‘Generalist’ 4 0.025 0.877 0.976 0.561 0%(B) 50%(A) 90%(A)

† Number of plots (N = 30) where that taxon was present. Significant values (P < 0.05) are highlighted in bold.

25 Table 2. Effects of shading and mulch depth on composite rainforest and pasture indices (ANOVA) and assemblage composition (PERMANOVA) of ordinal-sorted arthropods. Between-site effects are also shown. ‘Difference’ shows the results of post-hoc LSD (for composite indices) or permutation (for assemblage composition) tests (% levels with different letters are significantly different, P < 0.05). Df for shading, mulch depth, interaction and site are 2, 1, 2, and 4 respectively. Composite habitat indices were not calculated for all ‘specialist’ indicators as they occurred at less than four plots, or were absent altogether. P value

T† Shading (S) Depth (D) S x D Site Difference

Composite rainforest index ‘Increaser' indicators (Pitfall traps) 9 0.045 0.669 0.993 0.003 0%(A) 50%(B) 90%(AB)

‘Increaser' indicators (Litter extraction) 14 0.337 0.320 0.483 0.110 -

Composite pasture index ‘Increaser' indicators (Pitfall traps) 3 0.022 0.347 0.100 0.050 0%(B) 50%(AB) 90%(A)

‘Increaser' indicators (Litter extraction)‡ 1 - - - - -

Assemblage composition Pitfall traps n/a 0.006 0.448 0.548 <0.001 0%(A) 50%(B) 90%(B)

Litter extraction n/a 0.252 0.339 0.994 <0.001 -

†Number of taxa used for that composite indicator. ‡Composite habitat index was not calculated as only one component taxon was found. Significant values (P < 0.05) are highlighted in bold.

26 591 Table 3. Effects of shading and mulch depth on abundance scales of ant species: results only for species where the main effects of ANOVA P ≤0.05. Between-site effects are also shown. ‘Difference’ shows the results of LSD tests (levels with different letters are significantly different; A smaller, B larger, P < 0.05). Df for shading, mulch depth, interaction and site are 2, 1, 2, and 4 respectively. P value

Indicator category Freq† Shading (S) Depth (D) S x D Site Difference

Pitfall traps

Paratrechina QM1 ‘Generalist’ 13 0.051 0.838 0.026 0.051 -

Pheidole QM8 (mjobergi grp.) ‘Generalist’ 10 0.022 0.652 0.288 <0.001 0%(B) 50%(A) 90%(A)

Solenopsis QM1 ‘Generalist’ 28 0.051 0.503 0.857 <0.001 0%(AB) 50%(B) 90%(A)

Litter extraction

Hypoponera sp.1 Rainforest 'increaser' 8 0.044 0.210 0.871 0.099 0%(A) 50%(AB) 90%(B)

† Number of plots (N = 30) where that species was present. Significant values (P ≤ 0.05) are highlighted in bold. 592

27 Table 4. Effects of shading and mulch depth on composite rainforest and pasture indices (ANOVA) and assemblage composition (PERMANOVA) of ant species. Between-site effects are also shown. ‘Difference’ shows the results of post-hoc LSD (for composite indices) or permutation (for assemblage composition) tests (% levels with different letters are significantly different, P < 0.05). Df for shading, mulch depth, interaction and site are 2, 1, 2, and 4 respectively. Composite indices were not calculated for all litter-extracted ants, as less than 2 component species (T† < 2) were found from each index. P value

T† Shading (S) Depth (D) S x D Site Difference

Composite rainforest index ‘Specialist' indicators (Pitfall traps) 5 0.178 0.049 0.335 0.002 Deep(A) Shallow(B)

‘Increaser' indicators (Pitfall traps) 2 0.858 0.441 0.858 0.244 -

Composite pasture index ‘Specialist' indicators (Pitfall traps) 3 0.048 0.117 0.984 0.009 0%(B) 50%(AB) 90%(A)

‘Increaser' indicators (Pitfall traps)‡ 1 - - - - -

Assemblage composition Pitfall traps n/a 0.025 0.851 0.510 <0.001 0%(A) 50%(AB) 90%(B)

Litter extraction n/a 0.387 0.676 0.276 0.025 -

†Number of taxa used for that composite indicator. ‡Composite habitat index was not calculated as only one component taxon was found. Significant values (P < 0.05) are highlighted in bold.

28 593 FIGURE CAPTIONS

594 Fig. 1. Schematic diagram of one of the field experimental sites (distances not to scale),

595 showing criteria used when positioning experimental plots. ‘Shallow’ indicates

596 sterilised mulch placed at a depth of 3-5 cm, and ‘deep’ is 10-15 cm. The seven plots

597 were located randomly.(see text for more details).

598 Fig. 2. Effect of shading and mulch depth (S, shallow; D, deep) on composite rainforest

599 and pasture indices of ordinal-sorted arthropods. Values for rainforest and pasture

600 reference habitats (sampled the previous year) are also shown. The plots included in the

601 statistical analysis are represented by closed bars.

602 Fig. 3. Effect of shading and mulch depth (S, shallow; D, deep) on composite rainforest

603 and pasture indices of ant species. Values for rainforest and pasture reference habitats

604 (sampled the previous year) are also shown. The plots included in the statistical analysis

605 are represented by closed bars.

606 Fig. 4. Average soil moisture contents across the experimental treatments and unshaded,

607 un-mulched controls. Values for rainforest and pasture reference habitats are also shown.

608 All samples were taken in 2004. The plots included in the statistical analysis are

609 represented by closed bars.

610 Fig. 5. Temperature fluctuations over five days recorded at: (a) un-mulched, unshaded

611 control plots, rainforest and pasture reference habitats, and (b) plots with different

612 shading and mulch depths, with mean values and coefficient of variations (CV).

613 Temperature was recorded only from one site during April 2004. Horizontal lines are

614 drawn at 25 C˚.

29 Figure 1

Pasture Rainforest remnant

Shallow mulch 5-10 m Deep mulch

Shallow mulch

Deep mulch

Shallow mulch

Deep mulch

Legend Plot with 90% shadecloth No mulch (control) Plot with 50% shadecloth Plot with no shadecloth (0%)

615

616

30 FigureFigure 12

a Composite rainforest index (‘Increasers’, Pitfall traps) b Composite rainforest index (‘Increasers’, Litter extraction) 5 6

4 4 3

2 Index level level Index Index level level Index 2 1

0 0 PastureP NoneCon- 0% 0% SM 0% 0% DM 50% 50% SM 50% 50% DM 90% 90% SM 90% 90% DM Rain- RF Pasture Con- 0% 0% 50% 50% 90% 90% Rain- trol S D S D S D forest P N one 0% SM 0% DM 50% 50% 90% 90% RF trol S D SM S DM D SMS DM D forest

c Composite pasture index (‘Increasers’, Pitfall traps) 2

1 Index level level Index

0 PastureP NoneCon- 0% 0% SM 0%0% DM 50%50% SM 50%50% DM 90% SM 90%90% DM Rain- RF trol S D S D S D forest

617

618

31 FigureFigure 2 3

a Composite rainforest index (‘Specialists’, Pitfall traps) b Composite rainforest index (‘Increasers’, Pitfall traps) 2 6 1.5

4 1 Index level level Index Index level level Index 2 0.5

0 0 PastureP Con- N one 0% 0% SM 0% 0% DM 50% 50% SM 50% 50% DM 90% 90% SM 90% 90% DM Rain- RF PastureP NoneCon- 0% 0% SM 0%0% DM 50%50% SM 50%50% DM 90%90% SM 90%90% DM Rain- RF trol S D S D S D forest trol S D S D S D forest c Composite pasture index (‘Specialists’, Pitfall traps) 10

8

6

4 Index level level Index 2

0 PastureP NoneCon- 0% 0% SM 0% 0% DM 50%50% SM 50%50% DM 90%90% SM 90%90% DM Rain- RF trol S D S D S D forest

619

620

32 FigureFigure 4 3

60

50

40

30

20

Soil moisture (%) (%) moisture Soil 10

0 PasturePasture Con- 0m 0%Shal 0%lowW ood 0% 0m 50%Shal 50%lowW ood 50% 0m 90%Shal 90%lowW ood 90% Rain- RF trol S D S D S D forest

621

622

623

624

33 Mean CV FigureFigure 4 5 Control 20.84 23.92 a Pasture 20.02 6.23 18.28 3.50 35 Rainforest ) ˚ 30

25

Temperature (C Temperature 20

15 0 20 40 60 80 100 120 140 Mean CV 0% Shallow 23.21 7.66 b 0% Deep 22.15 8.43 35 50% Shallow 20.01 4.63 50% Deep 21.18 4.52 90% Shallow 19.52 3.52

) 90% Deep ˚ 30 20.02 3.64

25

Temperature (C Temperature 20

15 0 20406080100120140 Time lapsed (hour)

625

34