- New research indicates that even after 40 years of recovery, fast-growing tropical forests in Brazil house far fewer species and sequester less carbon than their primary counterparts.
- The study finds the most-recovered secondary forests surveyed had around 80 percent the biodiversity and carbon of nearby primary forests.
- To allow greater recovery of secondary forests and the wildlife and carbon they house, the researchers say policies should be put in place to better protect these forests and give them the time they need to mature properly.
- However, they caution that enacting policy is only one part of the solution, and urge more funding and attention be given to monitoring and enforcement of forest protection regulations.
With around half the world’s forest cover cleared or otherwise degraded at some point in the recent past, the new forests that pop up to replace them – called secondary forests – are often seen by conservationists as the next best thing. But just how well secondary forests compare to primary forests in terms of biodiversity and carbon storage has been a bit of a mystery.
Now, new research published in Global Change Biology sheds more light on the ecological value of secondary forests. It finds that even after 40 years of recovery, fast-growing tropical forests in Brazil house significantly fewer species and sequester less carbon than their primary counterparts. The study’s authors say that in order to meet their full ecological potential, established secondary forests need greater protection to allow them to recover more completely.
The study was conducted by a team of scientists from institutions in Europe, Brazil and Australia. They measured carbon content and recorded 1,600 plant, bird and dung beetle species in 59 naturally regenerating secondary forests of varying ages and 30 undisturbed primary forests in the eastern Amazon region of Brazil.
According to Gareth Lennox, a senior research associate at Lancaster University in the UK and lead author of the study, deforestation starting ramping up in this part of Brazil in the 1970s with the construction and expansion of the Cuiabá-Santarém Highway and Belém-Brasília Highway, along with policies that promoted cattle ranching in the region. Because of this, the oldest secondary forests there have been recovering for about 40 years.
Lennox and his team found that the most-recovered secondary forests had around 80 percent the biodiversity and carbon of nearby primary forests. Those that had only recently started to recover were pretty much empty of both.
“At one extreme, some of our secondary forests were located in recently abandoned agricultural areas. These forests had near-zero biomass, open canopies and very small complements of forest plants and animals,” said Gareth Lennox, a senior research associated at Lancaster University in the UK and lead author of the study. “At the other extreme, we also sampled secondary forests with biomass levels approaching regional undisturbed forest averages, fully closed canopies, and levels of species richness around 80% of that found in undisturbed forests.”
However, there’s a caveat to these high-performing recovering forests. The researchers explain that their study site represents a near-ideal situation for secondary forests, with areas of primary forest scattered throughout the region acting as reservoirs for wildlife. Animals and plants there can quickly move from these remnants back into cleared areas when the forest regenerates enough to provide habitat.
Such is not the case in other parts of Brazil or the elsewhere in the world, Lennox warns.
“Other forested regions of the tropics have suffered much higher levels of historic deforestation, resulting from much longer periods of human occupation,” he told Mongabay. “For example, large-scale disturbance of Brazil’s Atlantic forest can be traced back four centuries. As such, the land-use context of our study region likely provides a near best-case scenario for secondary forest recovery. In other contexts, recovery periods are likely to be far greater.”
To allow this recovery to happen, the researchers say policies should be put in place to better protect secondary forests and give them the time needed to mature properly. As an example, they point to the state of Pará, where a secondary forest protection mandate was enacted in 2014. Here, private landowners are required to apply for a license to log their forests. And if it turns out that their forests are older than 20 years or contain many large trees — criteria established by Lennox and his team — then they’re not allowed to log them at all.
“Through the application of these regulations – which are the first of their kind – secondary forest management is based on sound science, is open and transparent, and can deliver environmental and social benefits that would not be achieved in their absence,” Lennox said.
While Lennox and his colleagues see Pará’s policy as promising, they concede that it’s only been in place for a few years, which isn’t enough time to effectively assess its impact. They also say more must be done to make a difference on the larger scale.
Study coauthor Joice Ferreira from The Brazilian Agricultural Research Corporation says developing policy is “only one part of the process.” She underlines the need for greater monitoring and enforcement of regulations aimed at protecting Brazil’s recovering forests.
“Achieving this requires substantial increases to the funding of local environmental agencies,” Ferreira said. “Yet, in 2017 the Brazilian government cut funding to the Environment Ministry by 50%.
“Under these circumstances, laws that seek to protect and enhance Brazil’s forest will fail to achieve their potential.”
Banner image: The turquoise tanager (Tangara mexicana) is a very common inhabitant of secondary forests and forest edges
(even venturing into cities). Photo by Alexander C. Lees
Citation: Lennox, G. D., Gardner, T. A., Thomson, J. R., Ferreira, J., Berenguer, E., Lees, A. C., … & Moura, N. G. (2018). Second rate or a second chance? Assessing biomass and biodiversity recovery in regenerating Amazonian forests. Global change biology.