Identifying managerial legacies within conservation corridors using remote sensing and grasshoppers as bioindicators.

Abstract

Biodiversity conservation under global change requires effective management of key biodiversity areas, even areas not under formal protection. Natural grassland conservation corridors between plantation forests are such areas, as they improve landscape connectivity, mitigate the impact of landscape fragmentation, and conserve biodiversity. However, empirical evidence is required to identify the extent to which past management actions promote effectiveness of conservation corridors into the future. We address this issue using grasshoppers, which are well-established indicators of habitat quality. In particular, we assess grasshopper response within corridors to historic grassland photosynthetic activity using a 25-yr normalized difference vegetation index (NDVI) time series. We then use vegetation characteristics measured in the field to understand the potential mechanisms driving grasshopper response. Furthermore, we explore the efficacy of satellite remote sensing for monitoring grasshopper habitat using additive models. We found that grasshopper evenness responded positively to deviation in NDVI within a 3-yr period, whereas assemblage composition responded positively over a shorter time of two years. Grasshopper richness and evenness responded strongly to the local vegetation height and bare ground, whereas grasshopper assemblage composition also responded to plant species richness. We found a major negative impact of the invasive alien bramble (Rubus cuneifolius) on large-sized grasshoppers and species of conservation concern. Overall, the results illustrate the importance of maintaining primary high-quality habitat for maintaining grasshopper diversity, alongside removal of invasive bramble. We recommend prescribed burning to maintain high-quality habitat heterogeneity, with sites burned within three years. Furthermore, high-resolution satellite imagery is effective for monitoring grasshopper richness and assemblage composition response to changes in vegetation within the corridors. Grassland conservation corridors do conserve biodiversity, although effective management and monitoring needs to be in place to ensure biodiversity resembles that of neighbouring protected areas.