An assessment of the ecological restoration on Motuora Island

Abstract

Ecological restoration is increasingly being undertaken to reverse the declines in biodiversity and to restore ecosystem functioning in damaged environments. On New Zealand islands it is especially significant because islands act as refugia for the native biota because they are naively vulnerable to invasive predators widespread on the mainland. On Motuora Island restoration began two decades ago (in the 1990’s) and previous studies on the Island in 2004 indicated that the planted forest sites had native beetles establishing in them but not the same assemblage as in the unmanaged naturally regenerating sites. We resurveyed the flighted beetle fauna at planted, unmanaged and pasture sites to investigate what changes had occurred since last decade. We remeasured the vegetation plots established on the Island and conducted leaf litter experiments to measure the rate of decomposition at the planted, unmanaged and pasture sites. Beetle fauna from the 2004 study was assigned functional groupings to investigate functional differences across the sites. The results were that the flighted beetle fauna of the planted sites had converged on the unmanaged sites, as planted and unmanaged forests had similar native beetle diversity, abundance and composition. Vegetation changes were also detected and the planted forests have converged on the same stem density as the unmanaged forests. However, functional analysis revealed that in 2004 the ground beetle functional composition in unmanaged forest sites differed from both planted forest and pasture sites, with many more predatory beetles present in unmanaged forest sites. In both 2005 and 2014, litter decomposition was significantly slower in unmanaged forests than in other vegetation types. These results suggest that the efforts to restore Motuora Island are achieving success in restoring the Island’s flora and fauna, although it is not certain whether the functional diversity in planted sites will eventually resemble unmanaged assemblages. The decomposition findings indicate that ecosystem function still differs between planted and unmanaged forests, and may take more time to resolve naturally.