CORVALLIS, Ore. – An analysis of 50 datasets from more than 1,000 individual parcels of tropical and subtropical forest show that avian species richness declines fastest when those pieces of habitat are surrounded by areas that woodland birds find inhospitable.
The study by an international collaboration that included Matthew Betts of the Oregon State University College of Forestry suggests the conservation value of forest remnants could be greatly increased simply by working to give the areas around habitat patches more tree cover.
Findings of the project led by scientists in Brazil and at Slippery Rock University in Pennsylvania were published in the Proceedings of the National Academies of Sciences .
“Contrary to what some people have thought, our research shows that pockets of small protected areas, by themselves, aren’t enough to enable robust avian conservation efforts in the biodiversity-rich forests of the tropics and subtropics,” Betts said. “Even tiny forest fragments, a few acres or less, with moderate nearby tree cover hold some conservation value, but the value goes up massively when the surrounding landscape is more hospitable.”
In fragmented forest areas, species richness declines as forest remnant size goes down, and the magnitude of decline depends on how specialized the species are to their habitat and on the quality of the surrounding landscape, known as matrix.
Biodiversity loss, Betts noted, can lead to species extirpations that irreversibly alter ecosystems and impair their capacity to support ecosystem services such as pollination and seed dispersal. Threats to biodiversity are at crisis levels, he said, as almost 25% of assessed animal and plant species worldwide are threatened, with more than 1 million species facing declines .
“The research shows that conservation gains from investing in a more hospitable matrix in agricultural and urban areas are far greater than previously realized,” added co-author Carlos Peres of England’s University of East Anglia.
The international team of 58 researchers from 19 countries combined data from forest islands created by river damming and from forest fragments created by clear-cutting. Unlike islands in the ocean, which are often millions of years old, human-caused forest islands are similar to forest fragments and serve as a baseline for worst-case scenarios of forest fragmentation, the scientists note.
“Two forest remnants of the same size can support very different numbers of bird species,” said project co-lead Anderson S. Bueno of Brazil’s Instituto Federal de Educação, Ciência e Tecnologia Farroupilha (Federal Institute of Science and Technology Education in Farroupilha). “Those surrounded by farmland with nearby trees may host more than twice as many species as isolated remnants within reservoirs.”
The other co-lead, Chase D. Mendenhall of Slippery Rock, said he hopes the research will result in more-effective land-use policies.
“Ideally it will encourage governments and landowners to invest in wildlife‑friendly farming practices that support both biodiversity and agricultural productivity,” he said.
Data/statistical analysis
Animals
High-quality surrounding landscapes mitigate avian extirpations from forest remnants
1-Apr-2026