One of the first studies to map the impact of deforestation on biodiversity across entire regions of the Amazon has found a clear ‘threshold’ for forest cover below which species loss becomes more rapid and widespread.
By measuring the loss of a portion of the dominant species of large and medium-sized mammals and birds, and using the results as a bellwether, researchers at the University of Cambridge found that for every 10 percent of forest loss, one to two major species are wiped out.
That is, until the threshold of 43 percent of forest cover loss is reached. After that the rate of loss jumps up to eight major species gone for every 10 percent of forest lost.
While current Brazilian law requires individual landowners in the Amazon to retain 80 percent forest cover, this is rarely achieved or enforced. Researchers say that the focus should shift to maintaining 50 percent cover – just half the forest – but over entire landscapes rather than individual farms in a bid to stop accelerated loss.
Unless urgent action is taken to stem deforestation in key areas that are heading towards or have already dipped below the forest cover ‘threshold’ – which, according to the research team’s models, amounts to a third of the Amazon – these areas will suffer the loss of between 31-44 percent of species by just 2030.
The expansion of agriculture in recent decades means that around 41% of the original forest in the study region has been lost over just the last 40 years.’
Avoiding deforestation and focusing reforestation in the areas that teeter on the species loss threshold will be the most direct and cost-effective way to prevent further species loss in the Amazon region.