For tropical forest birds, old neighborhoods matter

Old, complex tropical forests support a wider diversity of birds than second-growth forests and have irreplaceable value for conservation, according to an Oregon State University-led exhaustive analysis of bird diversity in the mountains of southern Costa Rica.

During their surveys, researchers found similar numbers of bird species in secondary stands compared to stands comprised entirely or in part of old-growth forest. However, the bird community in secondary forest was clearly shifted towards non-forest species, and only old-growth forest stands tended to include rare birds and to benefit biodiversity across the entire landscape. Scientists reported their results this week in the Journal of Applied Ecology.

The findings are important because in some cases, conservation programs have focused on the potential benefits of secondary forests. Although secondary forests do have value for conservation, the study suggests that primary forests are necessary as sources of biodiversity and as a refuge for species that can colonize other sites that are being restored. Thus, these results suggest that a strategy focussing only on second-growth forests may not benefit conservation-relevant species. Indeed, such stands tend to support only a few common species that can survive in highly disturbed areas.

To reach their conclusions, a team led by Urs Kormann, a post-doctoral scientist in the College of Forestry at Oregon State University, surveyed bird communities in 49 forest fragments near the Las Cruces Biological Station in Costa Rica. They analyzed diversity within each fragment as well as from one stand to another. Much of the old-growth forest in the area has been cleared for pasture in the last 50 years, but about 30 percent of the old-growth remains in patches ranging from less than two to more than 2,500 acres. The study was conducted in the Coto Brus region, which borders Panama and varies from rolling hills to mountains more than 10,000 feet high.

Read the full press release.