A ‘threshold’ for deforestation’s effect on biodiversity in the Amazon rainforest has been uncovered by new research from Cambridge University.

When this newly revealed forest-cover deforestation threshold is exceeded, extinctions surge in the regions affected — with extinctions becoming both more rapid and also more widespread.

To explain — for every 10% of forest cover that is lost, 1-2 large to medium-sized mammals or birds go extinct, according to the new research. That holds true (more or less) up until ~43% of forest cover is lost (deforested) — when this figure is reached extinction rates surge to between 2-8 major species per 10% of forest loss. So, in the case of 50% forest cover loss, you could expect to see the extinction of 10-40 large to medium-sized mammals or birds. Extinction rates for smaller species are thought to follow similar patterns.

While laws currently on the books in Brazil require regional/individual landowners to retain 80% forest cover, these laws are generally ignored. And unenforced.

A recent press release provides more:

Researchers say that the focus should be shifted to maintaining 50% cover — just half the forest — but over entire landscapes rather than individual farms, in a bid to stop whole regions losing untold biodiversity by slipping below the 43% threshold at which species loss accelerates.

Unless urgent action is taken to stem deforestation in key areas that are heading towards or have just 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% of species by just 2030.

“These results support the need for a major shift in the scale at which environmental legislation is applied in Brazil and the tropics,” stated Dr Jose Manuel Ochoa-Quintero, from Cambridge University’s Department of Zoology, who led the study, published recently in the journal Conservation Biology.

“We need to move from thinking in terms of compliance at a farm scale to compliance at a landscape scale if we are to save as many species as we can from extinction.”

The new research was performed in a portion of the North West Amazon over 3 million hectares in size. This region was divided by the researchers into 1,223 squares of 10,000 km — 31 squares the selected as representatives of the spectrum of forest cover across the region (12-90% cover). Of these 31 squares, 27 consisted of private land, and 4 of protected areas (PAs) with near complete forest cover.

In these 31 squares the presence of 35 key species of mammals and birds — pumas, giant anteaters, red howler monkeys, etc — were monitored via a combination of: direct observation, recordings, footprints, feces, interviews with landowners and residents, etc. Interviews were done using photographs, recorded animal noises, and other means, as identifiers.

“This is not just a result of overall loss of habitat, but also reduced connectivity between remaining forest fragments, causing species to hunt and mate in ever-decreasing circles,” noted Ochoa-Quintero. “This fragmentation may be the key element of the ‘threshold’ tipping point for biodiversity.”

This fragmentation is being driven largely by ever growing industrial agricultural production in the region — in particular, soya and beef production.

“At the current rates, the number of 10,000 km2 landscapes in the Amazon that fall below the species loss threshold of 43% forest cover will almost double by just 2030. At current rates, by 2030 only a mere 22% of landscapes in the region will be able to sustain three quarters of the key species surveyed for the study.”

“The expansion of agriculture in recent decades means that around 41% of the original forest in the study region — some 2 million hectares — 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,” noted Ochoa-Quintero.

Easier said than done though. After all, there’s money to be made, and growing populations of people to be fed. Is anyone ever going to really be able to convince someone that a puma or howler monkey off in a forest somewhere is more important than their “right” to live a modern lifestyle and/or eat the way that modern people do?

Image Credit: Public Domain