The white-plumed Antbird (Credit: Philip Stouffer/LSU)
One of the big questions that keep getting raised in relation to tropical forests is will species return when deforested areas are replanted. This so called secondary forest may not be as diverse as the original primary forest. With REDD programmes about to take off it’s an important question to answer.
Latest research published in PLoS seems to indicate that, where understory bird species are concerned, secondary forest could bring back almost as many species as was originally lost – but not all of them. The new study looked at forest fragments left after forest clearance for agriculture. The study lasted 25 years and covered the original clearance in the early 80′s right up to 2007 and the consequences of allowing the cleared areas to revert to secondary forest.
Most bird species returned to area with secondary growth forests.
The good news is that of the 101 understory birds species that were lost during the original clearence by 2007 97 of those species had returned to the forest fragments that was now contained within secondary forest areas.
Lead author Philip Stouffer, an ornithologist at Louisiana State University and co-authors of the paper, Erik Johnson at the National Audubon Society; Richard Bierregaard at the University of North Carolina, Charlotte; and Thomas Lovejoy at The Heinz Center in Washington, D.C., measured bird populations over 25 years in 11 forest fragments ranging from 2.5 acres to 250 acres in the Amazon rainforest near Manaus, Brazil.
“Through long-term observations of fragmentation in tropical forests, this study provides verification that local extinction is accompanied by continual recolonization, dependent on habitat size,” said Saran Twombly, program director in NSF’s Division of Environmental Biology, which funded the research.
Locally extinct birds returned over time.
The long term project highlighted that many species could recolonise areas even when habitat changes took place – if the species were given enough time. The study looked at the number of bird species before the areas were cleared and then again in 1985, 1992, 2000 and 2007 to monitor the ongoing effects.
Stouffer said. “Early on, the small fragments lost most of their understory birds, and the area that was cut had no forest birds at all.”
As you would expect the smallest forest fragments left after clearance had the most species losses with upto 70% lost in the smallest fragments. Larger areas that had been left lost as few as 10% of it species.
Bird species in forest fragments live in a state of flux.
By 2007 many of the areas being studied which had been cleared for cattle and other agriculture had less agricultural activity and were recovering to secondary forest status. In one of the areas before deforestation took place the researchers had netted 101 species of understory birds. By 2007 the number of species recorded had returned to 97.
“A handful of species have ‘gone extinct,’ but many more species are in flux,” Stouffer said. “They come and go.”
“Our samples are snapshots in time,” said Stouffer. “They show that forest fragments have the potential to recover their biodiversity if they’re in a landscape that can rebound. They’re not doomed.”
“If we consider a balance of abandoned and returned forests, within a 20-year window, birds will begin to treat the fragments as continuous forest,” Stouffer said.
“Although a small subset of species is extremely vulnerable to fragmentation and predictably goes extinct, developing second-growth forest around fragments encourages recolonization.”
One of the conclusions that the researchers came to was that local biodiversity in fragments was more to do with local turnover of species rather than any reflection on the status of the species as a whole.
Encouraging news for reforestation projects.
It’s encouraging news to see that species will return and recolonise deforested areas that are allowed to recover. While secondary forest will not provide the diversity of plant species which was originally in an area the news that it can bring back the majority of bird species is welcome. If the same response can be found to other types of species such as canopy birds or reptiles then REDD projects could help to re-establish thriving biodiversity in previously forested areas that have been severely degraded for one reason or another.
