Managing Soil Macrofauna Biodiversity in Geothermal Sites

Abstract

In New Zealand, geothermal ecosystems are among the rarest ecosystem types, and provide habitat for rare and in some cases unique thermophilic, extremophilic and thermotolerant species of plant, animals and microorganisms. Yet they are under threat both from surface activities such as farming practices on adjacent land and from extractive uses of the geothermal resource that draw heat and fluid away from the host surface geothermal features. Scientific research is the basis for the sustainable management of natural resources, and geothermal sites present some unique challenges. The plant species composition of most geothermal habitats has been well-studied, as has to a lesser extent the surface fauna, mainly invertebrates. The microbial communities associated with geothermal water and mud are increasingly under investigation as DNA techniques are developed that enable easy recognition of species composition, some of which may have useful industrial or medical applications. This paper presents the results of the first studies undertaken of the soil-dwelling macrofauna in geothermal areas, commissioned by Waikato Regional Council. Many worm and beetle species are able to colonise geothermal soil, with their diversity and numbers influenced by soil temperature, pH, and toxicity, and canopy cover. Organisms found include native and introduced species, including subtropical species existing well outside their normal geographic range. Some introduced species may pose a pest threat should their range become more extensive because of climate changes or changes in land use practices. In some areas of geothermal vegetation no soil-dwelling organisms were found. This raises questions about how normal nutrient cycling processes occur in these habitats. Maintaining ecosystem health is key to managing natural resources in geothermal ecosystems. Soil-dwelling macrofauna in geothermal areas depend on the presence of undecomposed litter in which the roots of thermophilic plants form a mat isolated from the hot soil. Whether these macrofauna complete all or part of their life cycle in this environment poses questions about the interconnectivity of geothermal and non-geothermal ecosystems and the role of suitable buffer zones of non-geothermal native vegetation in which the organisms can complete certain stages of their lifecycle and contribute to ecosystem services such as nutrient cycling and pollination,. The role of mitigation and restoration is discussed within the context of the role of the raised root mat and the implications of a very fragile ecosystem that may require several essential components for functionality Management tools facilitate the management of natural resources. A ranking system is presented to rate the quality and anthropomorphic disturbance at individual geothermal sites. A decision tool is provided to facilitate the prioritisation of management objectives that would give best value for resource investment at an individual site basis. The tool also facilitates the identification of sustaining linkages between both geothermal and non-geothermal plant and animal communities and the role and dimensions of buffers to increase the resilience of what are currently many island geothermal ecosystems surrounded by pasture, exotic forestry or native vegetation.