Webs of well-designed conservation corridors maintain river ecosystem integrity and biodiversity in plantation mosaics

Abstract

Landscape transformation and subsequent habitat loss locally extirpate populations and threaten ecosystem health. Timber plantations are a major threat to grassland ecosystems globally. An effective mitigation measure is the instigation of webs of large conservation corridors as ecological networks in plantation mosaics. These ecological networks incorporate natural water courses along with their matrices of natural grassland. Dragonflies are highly sensitive to habitat condition and are effective bioindicators of water quality. Here, we compare dragonfly diversity in conservation corridors, with nearby protected areas as controls, to determine the effectiveness of ecological networks for maintaining river ecosystem integrity, in the KwaZulu-Natal Midlands, South Africa. We also investigate the effect of ecological network corridor width on dragonfly assemblages. Lastly, we explore the importance of 18 environmental variables as drivers of dragonfly diversity. Dragonfly abundance, species richness, and Dragonfly Biotic Index scores (a scoring system based on dragonfly range of extent, threat status, and environmental sensitivity) did not differ between ecological network and protected area sites. Dragonfly abundance and species richness were positively correlated with ecological network corridor width. Landscape and water variables were the most important drivers of dragonfly assemblage composition in both ecological networks and protected areas. Management variables and those related to anthropogenic disturbance were not as important. This highlights the conservation success of these well-managed ecological networks for maintaining dragonfly biodiversity in forestry plantations, provided that corridors are wide enough. Implementation of ecological networks as a mitigation measure for plantation forestry is highly effective for lotic systems, and should be implemented more widely in environmental protection plans for transformed landscapes.