Expanding forests can be bad news for the environment

A new study, The biodiversity cost of carbon sequestration in tropical savanna by Abreu et al. in Science Advances, has examined the past 30 years in the Brazilian Cerrado. Over this period the local authorities have encouraged fire suppression to reduce damage to the local environment and as a result the tree cover has increased greatly. However, the authors found that in areas fully encroached by forest, plant species declined by 27 percent and ant species declined by 35 percent.

For a few species, fire suppression is a clear cause, as they need fire to germinate. However for many plants afforestation leads to a slow death. The chief problem is low light.

William Hoffmann, professor of plant and microbial biology at NC State and co-corresponding author the paper, said. “Shady conditions are an enemy to these savanna dwellers. Many of these plant species just can’t persist in a forest. However, fire suppression has taken root in Brazil, so there is a reluctance to allow fires – even to promote the health of the savanna.”

Perhaps more importantly, Hoffmann said, losses of plant and ant species unique to the savanna were even more widespread. Savanna plants declined by two-thirds in lands that converted from savanna to forest, while savanna ants declined by a whopping 86 percent.

“These savanna species can’t be moved and can’t really live anywhere else,” Hoffmann said. “This study really highlights the extent to which these species are dependent on their savanna homes.”

The report contradicts earlier studies that have suggested increasing forests result in a net increase in plant species. Abreu et al. argue that earlier surveys have overlooked the high diversity of shrubs and herbaceous plants in savannas, by focussing on trees. This matters as three quarters of the plant species in the Cerrado are shrubs and herbaceous plants.

The findings could have more far-ranging implications, as Hoffmann added that he would expect to find similar results in other tropical areas where savannas become degraded by suppressing fire. They conclude that it is urgent that current policies are reexamined to see where fire can be included in conservation practice.

Souce: Eurekalert / NC State