The effects of restoration on the structure and function of litter invertebrate communities in New Zealand native forest remnants : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Palmerston North, New Zealand

Abstract

Much of New Zealand‘s remaining lowland forest exists as small, often degraded and heavily disturbed remnants on private farmland. Disturbances, such as livestock grazing and browsing by mammalian pests, are known to have a detrimental effect on native vegetation of these remnants. However, it is unclear what impact these disturbances have on the structure and function of forest floor invertebrate communities. Existing studies of forest fragmentation have predominantly focused on the effects of remnant area and shape, rather than remnant condition. This study examines how litter invertebrate habitat, community structure, and leaf litter decomposition, vary between grazed and ungrazed (fenced) remnants of differing size, and nearby forest reserves. Secondly, I examine how invertebrate community structure and function recover with time since livestock exclusion, with and without additional mammalian pest control. I found that grazed remnants provide dramatically altered habitat for litter invertebrates, compared to fenced remnants and large forest reserves. Grazed remnants are typified by having higher soil compaction, minimal understorey vegetation, and reduced litter cover. Consequently, grazed remnants have depauperate, yet highly variable invertebrate communities, compared to fenced remnants and forest reserves. Even very small forest remnants can support litter invertebrate communities very similar to that of larger forest reserves, provided they are protected from livestock grazing. Furthermore, invertebrate communities show strong recovery over time since livestock exclusion, particularly when livestock exclusion is combined with mammalian pest control measures. I found that litter decomposition rates did not differ between management treatments in my first observational study. However, in the second observational study, leaf decomposition rates at the edge of remnants increased with time since livestock exclusion, suggesting that restoration actions can lead to changes in ecological functioning. Small native forest remnants have high ecological value and substantial restoration gains can be made through the relatively simple action of fencing to exclude livestock.