The loss of forests means a loss of biodiversity. That’s a no-brainer. Yet simply replanting trees, thereby allowing for secondary forests in the place of bygone primary forests, is no substitute for keeping primary forests intact in the first place. That’s because secondary forests pale in comparison to primary forests when it comes to species diversity and carbon storage capacity, says an international team of researchers.
Even after four decades years of recovery, woods allowed to regrow in formerly forested areas remain poor in species as opposed to the natural biodiversity of undisturbed primary forests. That does not mean, of course, that secondary forests are not important for biodiversity. Even secondary forests with relatively low diversity of species is better than no forest at all.
The team of scientists, who come from Europe, Australia and Brazil, surveyed more than 1,600 species of plant, bird and dung beetle in 59 naturally regenerating secondary forests and 30 undisturbed primary forests in the eastern Amazon. They published their findings in the journal Global Change Biology, demonstrating that primary forests contain more biodiversity and carbon storage capacity than even mature regenerating forests.
“We found that the carbon and biodiversity of secondary forests recovered to more than 80 per cent of levels found in undisturbed primary forests,” the study’s lead author Dr. Gareth Lennox from Lancaster University in the United Kingdom explains.
“This is undoubtedly good news for climate change mitigation and biodiversity conservation,” Lennox elucidates. “Nevertheless, the regions we assessed provide very favourable regeneration conditions, with greater than 50 per cent remnant primary forest cover and, consequently, large populations of forest species that can colonise secondary forests. Even in this situation, secondary forests cannot substitute for undisturbed primary forests, which must remain a priority of conservation efforts.”
In other words, whereas replanting forests is a worthy cause, a primary aim of conservation should focus on saving primary forests from further degradation at the hands of loggers and developers.
In developing countries like Brazil, the authors explain, people from rural areas in forested regions tend to migrate to nearby cities in search of better economic prospects. This reduces the number of farmers, which in turn allows woods to start to regenerate. In the past three decades the area in the Brazilian Amazon occupied by secondary forests has grown from less than 30,000 square kilometers to more than 170,000sqkm, twice the size of Austria. Less encouragingly, tropical primary forests continue to be decimated in Brazil with an area the size of Austria cleared of trees each year.
“In the Brazilian Amazon, the average time before secondary forests are deforested again is just five years,” Professor Jos Barlow, a study co-author from Lancaster University, says. “Moreover, across the tropics, secondary forest management regimes are beset by legal uncertainties, inconsistent decision-making, and the chronic undervaluation of these important ecosystems,” Barlow elucidates. “For secondary forests to achieve the socio-ecological potential we uncover, where sites have been regenerating for up to 40 years, they must be incorporated as key elements of landscape management and conservation planning.”
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