Wednesday, June 06, 2007

Climate Change, Land Use, and Bird Diversity

A study published this week in the open-access journal, PLoS Biology, argues that many species of birds face range reduction due to climate change and landscape alteration. Approximately 400 of the 8750 species studied will lose more than half of their range by 2050. That number could rise to 900-1,800 species by 2100. The largest effects on bird diversity are expected to occur in the tropics because many ranges there are already small.

The study used four scenarios for climate change and land alteration derived from Millennium Ecosystem Assessment models. The scenarios present the likely future distribution of 18 types of land cover under different models of economic development (globalization vs. regionalization) and conservation actions (proactive vs. reactive). Maps created from those scenarios were compared against the current distribution of 8,750 birds (pdf) to identify species that are likely to suffer range loss. (1,125 species (pdf) were not included; most of these appear to be waterfowl, seabirds, gulls, and waders, which are somewhat less dependent on land cover.)

Changes in land cover are likely to be concentrated in high latitudes and in the developing world. At high altitude the changes are predominantly due to climate change. In Central and South America, central Africa, and southern Asia, development and deforestation play a more critical role than climate change. Changes due to economic development rather than climate change would be a greater factor when ecosystems are managed reactively (addressing problems only after they occur) rather than proactively. Consequently, range reductions are likely to be greatest without active environmental protection.

The authors identify several factors that could alter their results. One factor that could worsen range loss for some species is habitat specialization. The effects of disease and invasive species will have their own impact, as well. Range shifts and adaptation to new habitat types could mitigate loss for other species.

If these results are accurate, reducing future extinctions among bird species will require solutions to two problems. Reductions in greenhouse gas emissions will be necessary to prevent large-scale range loss and possible extinctions at higher latitudes. In areas closer to the tropics, controlling climate change still plays a role, but preventing habitat loss through expansion of protected areas and other conservation actions is more important in the immediate future.

The maps below show the likely landscape changes due to climate change and development, and the likely distribution of range reductions (click to enlarge).

(A, B) Patterns of change in land cover due to land-use and climate change by 2100. (C, D) The resulting potential impact for birds: the pattern of richness of species with projected range declines ≥50%. This represents the summed, current-day occurrence of qualifying species across a 0.5° grid. Patterns are given for the environmentally proactive “Adapting Mosaic” scenario (A, C), and the environmentally reactive “Order from Strength” scenario (B, D). Maps are in equal-area cylindrical projection. Colors in C and D vary from dark blue to dark red, and the legends provide labels for select colors along this continuous scale (minimum, ~1/3, ~2/3, maximum of data). From: Projected Impacts of Climate and Land-Use Change on the Global Diversity of Birds Jetz W, Wilcove DS, Dobson AP PLoS Biology Vol. 5, No. 6, e157 doi:10.1371/journal.pbio.0050157