Matrix habitat restoration alters dung beetle species responses across tropical forest edges

Abstract

External threats from agricultural intensification, fire encroachment, species invasion and illegal harvesting present major conservation challenges in isolated tropical forest remnants. These processes can greatly exacerbate the magnitude of edge effects as the degree of patch to matrix contrast increases. Theory suggests that mitigation of these effects should be possible through conservation strategies that remove external threats and restore adjacent matrix structure, but this has not been tested experimentally. In the rapidly-dwindling Afromontane rainforests of Nigeria, where nature reserves have the least protection of all African conservation areas, we created an experimental matrix restoration treatment in which we excluded livestock by fencing, maintained a fire-exclusion break, and passively revegetated a 200m buffer zone in the surrounding matrix at replicated edges. After three years, dung beetle communities in remnant forests showed a 53% increase in abundance at sites adjacent to the restored matrix. Over 90% of the common dung beetle species differed in the magnitude of their edge responses between forest-to-restored versus forest-to-degraded matrix sites. Moreover, a significant difference in species richness across the forest-to-degraded matrix edge became non-significant following matrix restoration, and there was also a significant decrease in community dissimilarity across the edge gradient in these regenerating sites. Just three years after excluding threatening processes from comparatively small areas of matrix habitat, we found that these efforts not only reduced edge effects, but also (1) enhanced dung beetle populations in the adjacent reserve, (2) led to an increase in dung beetle capture rates in the regenerating matrix, and (3) facilitated re-establishment of species that were absent due to matrix degradation. Therefore, regenerating buffers can substantially increase effective reserve size and restore invertebrate communities in landscape mosaics where remnant habitats are embedded within anthropogenic landscapes.