The interactive effects of livestock exclusion and mammalian pest control on the restoration of invertebrate communities in small forest remnants

摘要

In many agricultural landscapes, significant biodiversity gains can be made by improving the ecological condition of degraded remnants of semi-natural habitat. Recent emphasis has been on the level of management intervention required to initiate vegetation recovery in small forest remnants, but no comparable emphasis has been placed on benefits for invertebrate communities. In the Wai-kato region, New Zealand, we tested the effects of livestock exclusion, mammalian pest control, and their interaction, on leaf-litter invertebrate communities in 30 forest remnants, using a space-for-time substitution approach. A total of 87 376 invertebrates were extracted from 964 leaf-litter samples. Invertebrate density was an order of magnitude lower in remnants than in nearby large forest reserves. For key taxa, such as Diplopoda, Isopoda, Coleoptera and Mollusca, 10- to 100-fold lower densities were recorded in remnants with no pest control, particularly where livestock were not excluded. By contrast, other taxa such as Thysanoptera and Formicidae (Hymenoptera) had up to 100-fold greater densities in remnants with recent stock exclusion and pest control. These changes led to a significant livestock exclusion x pest control interaction effect on the degree of invertebrate community dissimilarity between forest remnants and forest reserves. Using structural equation modelling, we found that treatment effects were largely mediated by a cascading series of indirect causal paths involving altered soil chemistry, vegetation composition, and litter mass relative to large forest reserves, although the livestock exclusion x pest control interaction was inadvertently confounded with differing slopes and areas of remnants in different treatments. Livestock exclusion and mammalian pest control have significant, but contrasting, effects on invertebrates in the first 10-20 years following livestock exclusion from forest remnants, with mammalian pest control having limited benefit for the leaf-litter invertebrate fauna without livestock exclusion.