By T. Trevor Caughlin, Literature Coordinator
Recovery of animal populations, particularly visible and charismatic species, is often listed as a public benefit of habitat restoration. However, our knowledge of how tropical forest restoration promotes wildlife is hampered by a lack of long-term data. A new paper, by Amanda Freeman and co-authored by PARTNERS member Carla Catterall, describes the trajectory of rainforest bird communities in restored rainforest sites over two decades. By quantifying the long-term prospects for bird communities, as well as the bird functional traits and restored site characteristics that influence recolonization, the new research could lead to better management for rainforest-dependent bird species in secondary forest.
The study took place in a network of sixteen restoration sites, planted with rainforest tree species in the 1980’s. The restoration sites are spread across 700 km2 of the Atherton Tablelands region of the Australian wet tropics, a largely agricultural landscape with few remnant patches of old growth forest. The restoration sites were surveyed for birds in 2001 and in 2008, 10-24 years after tree planting had taken place and canopy closure had occurred at all sites. Bird species were classified into groups based on their specialization for rainforest habitat and predicted patch colonization ability. Restoration sites were defined by their landscape context, including percent rainforest cover in 200 m. Bird communities at the restoration sites were then compared to eight reference sites with old growth rainforest.
The study’s major finding was that even after more than a decade of forest regrowth, the restoration sites were more similar to one another and to surveys conducted seven years earlier than to old-growth reference forest. Bird functional traits were a significant predictor of recolonization, and rainforest-dependent species, including birds that were edge-avoiders, sedentary or dietary specialists, were significantly less likely to colonize restored patches. Evidence that recolonization is a barrier for birds was also found in analyses of landscape context on avian communities, which revealed a significant decrease in rainforest-dependent bird occupancy when nearby (<200 m) remnant rainforest cover was low. These findings suggest that a realistic timeline for avian community recovery in restored forest may be on the order of decades, even for sites where restoration of forest structure has been largely successful, including a closed canopy of native tree species. The results also reveal the critical importance of spatial planning, including placing restoration sites near to old growth forest, if restoring rainforest bird communities is a major goal. Another potential solution for slow avian colonization of restored forest could be to increase the area of restoration sites—a strategy that could alleviate edge effects and provide a greater variety of dietary niches. Overall, the new research adds to a growing body of evidence that a long-term and large-scale perspective is necessary for research and management of tropical secondary forests.
Photo credit:
Macleay’s Honeyeater by JJ Harrison ([email protected]) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
