PARENT SESSION
Organized Oral Session 28: Ecological processes important in the responses of bird populations to environmental change driven by agriculture
Organizer(s): K Norris, E Chambers, and J Vickery
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 511a, Level 5, Palais des congrès de Montréal
Long-term responses of understory birds in Amazonian forest fragments to local matrix dynamics.
Stouffer, Philip*,1, Bierregaard, Richard2, Strong, Cheryl 3, 1 Louisiana State University, Baton Rouge2 University of North Carolina- Charlotte, Charlotte3 San Francisco Bay Bird Observatory, Alviso, CA
ABSTRACT- The rainforests of the Amazon basin are being converted at a rate of over 1,500,000 ha/year. The rate is currently increasing, and may lead to over 2/3 of the Amazon being degraded by 2020. Forest loss inevitably leads to smaller and more isolated patches of forest, with remaining patches often in the 1-100 ha range. Studies of the effects of fragmentation typically consider the consequences of fragment size, landscape-level forest cover, or time since isolation on forest biota. Based on 20 years of bird sampling in fragments in a dynamic Amazonian landscape, we show that the condition of the matrix habitat surrounding fragments can often be as important as fragment size or forest cover in explaining variation in understory bird abundance. Fragments surrounded by 100 m of open pasture can experience reductions in understory bird abundance of over 95%, including complete absence of some insectivore guilds, even in landscapes dominated by continuous forest and old second growth. We suggest that these extreme reductions may be expected throughout Amazonia in small (< 10 ha), isolated rainforest fragments. At the same time, abundance for some guilds returned to preisolation levels in 10 ha and 100 ha fragments connected to continuous forest by 20 year old second growth. Our results show that the consequences of Amazonian forest loss cannot accurately be described without explicit consideration of vegetation dynamics in matrix habitat. Any dichotomous classification of the landscape into "forest" and "non-forest" misses essential information.
Key words: fragmentation, matrix habitat, landscape change, bird communities