If we plant the plants do the insects follow? An assessment of indigenous invertebrates in an urban forest remnant and restoration sites in Christchurch

Abstract

Urbanisation has led to substantial loss and fragmentation of natural habitat. Native ecosystems have been detrimentally affected through this habitat loss along with reduction of habitat quality and the introduction of non-native plants and animals. The impact of urbanisation can be reduced by the protection and restoration of remnant habitat along with re-vegetation of suitable areas with indigenous plant species. Through public interest and community group participation urban restoration has increased globally, with the motivation to re-create ecological processes which support native flora and fauna. Successful restoration should restore biological functions and the integrity of ecosystems but this is often only evaluated on the success of establishing native plant cover. The hypothesis of 'if you build it they will come' is seldom tested. This study aims to assess the importance of remnant indigenous habitat to the success of restoration projects and if restoration is achieving the goal of re-creating ecological processes. This aim was accomplished by surveying the biodiversity and abundance of terrestrial invertebrates. They constitute a wide range of functional groups and are major contributors to almost all ecological processes and thus valuable and increasingly used indicators of ecosystem integrity and function. This study repeated one done by Richard Toft in 2003 where invertebrates of the old growth remnant forest of Riccarton Bush, suburban gardens and the restoration site of the Wigram Retention Basin were sampled. Two other restoration sites, Travis Wetland and Styx Mill Reserve, within Christchurch City were also included in the repeated survey of 2013. Results from the 2003 survey showed that Riccarton Bush was well differentiated from the suburban gardens and the restoration site of Wigram Retention Basin. The restoration site was more similar to the suburban gardens than the remnant old growth forest. The repeated survey ten years later in 2013 showed similar results, the restoration site of Wigram Retention Basin was still similar in species richness and abundance to the suburban gardens than Riccarton Bush. The site most similar to Riccarton Bush was an area in Travis Wetland that contained old growth manuka (Leptospermum scoparium). Indications from this study reflect others; the succession of restoration sites to fully functioning ecosystem takes time. The establishment of suitable habitat, the surrounding landscape matrix and dispersal ability impact on the capacity of species to colonize restoration sites. The key to the enhancement of native biodiversity in an urban setting is the restoration and maintenance of remnant vegetation and the success of restoration projects. The findings of this study contribute to the understanding of the requirements needed for the invertebrates to follow the plants and whether some management changes are required to achieve a positive ecosystem outcome.