Quality not just quantity – Why stemming deforestation in the Amazon isn’t enough
Most people would consider policies designed to conserve 80% forest cover in the Amazon to be a success story. However, these forests may lose up to 54% of their potential conservation value from human disturbances in modified landscapes and within the remaining forest. The IAE’s Professor Ralph Mac Nally and a team of international scientists are the first to measure the combined effect of landscape change and within-forest disturbances in tropical forest landscapes.
The researchers looked at a range of disturbed landscapes, from largely pristine primary rainforest through to cleared areas in the Brazilian state of Pará, which includes a quarter of the Brazilian Amazon. Birds, trees, understory plants and dung beetles (which are a ‘proxy’ for ecosystem processes such as nutrient cycling) were sampled, constituting about 2000 species. The broad range of species considered also makes the study unique because previous work has focused on single taxa.
Disturbance was either ‘landscape disturbances’, which includes subsidiary effects of deforestation such as vegetation fragmentation and edge creation, and ‘within-forest disturbances’, which include selective logging and wildfires. Professor Mac Nally and other team members analyzed the data to measure how severely each area was affected by the multiple disturbance processes. Conservation value should be proportional to forest cover in the absence of landscape or within-forest disturbance, so that the deficit relative to this expected conservation value is a measure of the effect of disturbance (the ‘conservation deficit value’).
The findings of the study were alarming – even were land holders to comply with the Brazilian Forest Code, the forests may only retain 46–61% of their potential conservation value. The Forest Code specifies that private land holders must maintain 80% of their forest cover or offset the deficit if their holdings have less than 80% cover. The deficits are significant because about 53% of Brazil’s native vegetation is on private property.
“If you don’t account for both landscape disturbance and within-forest disturbances, then you will significantly underestimate biodiversity loss,” said Professor Mac Nally. “You don’t have to disturb the forest very much to get a substantial loss of biodiversity above the effect of the loss of forest cover in its own right.”
“I think it’s great there is a target to maintain 80 percent forest cover,” Mac Nally continued “but we need to remember this means that land owners with more than 80% can still reduce their cover down to 80%. Offsets are often geographically distant from the forest they are intended to replace, and the species that are meant to be protected may not occur in those distant areas. We are looking at ways to improve the Forest Code to benefit both biodiversity conservation and to reduce opportunity costs to the land holder. Win-win solutions are needed to have a better chance of compliance by land holders.”
This study was published in Nature in June 2016. You can read more about it here.