Resilience of New Zealand indigenous forest fragments to impacts of livestock and pest mammals
- AgResearch Grasslands, Private Bag 11008, Palmerston North 4442, New Zealand
- Landcare Research, Private Bag 3127, Hamilton 3240, New Zealand
- School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
- School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
- Present Address: School of Animal Biology, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia and CSIRO Entomology, Centre for Environment and Life Sciences, Underwood Avenue, Floreat WA 6014, Australia
- School of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand
A number of factors have combined to diminish ecosystem integrity in New Zealand indigenous lowland forest fragments surrounded by intensively grazed pasture. Livestock grazing, mammalian pests, adventive weeds and altered nutrient input regimes are important drivers compounding the changes in fragment structure and function due to historical deforestation and fragmentation. We used qualitative systems modelling and empirical data from Beilschmiedia tawa dominated lowland forest fragments in the Waikato Region to explore the relevance of two common resilience paradigms – engineering resilience and ecological resilience – for addressing the conservation management of forest fragments into the future. Grazing by livestock and foraging/predation by introduced mammalian pests both have direct detrimental impacts on key structural and functional attributes of forest fragments. Release from these perturbations through fencing and pest control leads to partial or full recovery of some key indicators (i.e. increased indigenous plant regeneration and cover, increased invertebrate populations and litter mass, decreased soil fertility and increased nesting success) relative to levels seen in larger forest systems over a range of timescales. These changes indicate that forest fragments do show resilience consistent with adopting an engineering resilience paradigm for conservation management, in the landscape context studied. The relevance of the ecological resilience paradigm in these ecosystems is obscured by limited data. We characterise forest fragment dynamics in terms of changes in indigenous species occupancy and functional dominance, and present a conceptual model for the management of forest fragment ecosystems.