Conserving New Zealand’s endemic carnivorous land snail Powelliphanta patrickensis through restoration of a functioning ecosystem : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

As of 2014, New Zealand’s largest active opencast mine, covering approximately 2500 hectares, and located on the West Coast of the South Island has been granted an extension that will further impact the diverse range of native and endemic flora and fauna in the area. Powelliphanta patrickensis, a locally endemic carnivorous land snail, will be subject to restoration and relocation programmes as a result of habitat loss. Mining of this type requires the complete removal of ecosystems, including vegetation, soil and rock to access the mineral resources beneath, impacting a range of species and ecological processes. Soil and rock are then stored in large, mixed stockpiles that can become depleted in volume, organic matter and nutrients. A number of restoration measures are already undertaken on site including: vegetation direct transfer (VDT), where intact sods of topsoil, flora and fauna are lifted and transplanted to a holding site or site requiring restoration; addition of biosolids to stockpiled soils to restore organic matter and nutrient levels in stockpiled soil; and spread of untreated soil stockpiles. The objectives of this thesis were to test the efficacy of the current restoration methods and further develop ecological restoration practices following mining to inform decision-making concerning restoration, with an initial focus on P. patrickensis. Molecular analysis of P. patrickensis diet showed that this species has a relatively generalist feeding behaviour consisting predominantly, if not exclusively, of endemic earthworms. Notable seasonal variation occurred between summer and winter diet composition, and comparison to the closely related but allopatric species Powelliphanta augusta showed a strong difference in diet composition. Such analyses support the notion that flagship species do not necessarily represent the needs of other, even closely related, species. The impact of biosolids amendment on a key earthworm species (present in 22% and 77% of P. patrickensis and P. augusta diets respectively) was assessed in a glasshouse experiment. Biosolids addition led to total earthworm mortality, compared to significantly lower mortality rates in pots containing ‘unmodified’ native and untreated stockpiled soil. Biosolids, however, doubled plant growth compared to controls, and both biosolids and earthworms benefited soil community and function. Subsequent work investigated the response of various other ecosystem processes to VDT, biosolids amendments and stockpiled soil. Soil microbial activity, biomass, community-level physiological profile and functional diversity were examined in a field setting. VDT was the most effective restoration technique, followed by biosolids treatment, and then stockpiled soil spreads. Reconciling results with studies of the effects of restoration protocols on earthworm species richness and abundance led to the recommendation that VDT is a preferable restoration type, and that P. patrickensis should be relocated only to VDT or undisturbed native sites when being translocated. Responses of other ecosystem functions, including plant-arbuscular mycorrhzal fungal (AMF) interactions and their effects on plant growth and soil microbial communities, to restoration practices were examined in glasshouse experiments. It was found not only that native vegetation was sensitive to the AMF species present, but also that biosolids disrupted colonisation of plant roots by AMF. Rather than pursue a ‘flagship’ or ‘keystone’ species approach focusing on a single species, this thesis used the legal, conservation and media attention that P. patrickensis attracted, to investigate a range of ecosystem-wide processes that inform site restoration. Recommendations for restoration should be supported by strong empirical evidence, and this thesis has provided a basis for further work on complex ecological interactions associated with restoration of opencast mining.