The Many Threats to Biodiversity in Brazil

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A study finds less intrusive activities double our overall impact on biodiversity in the forests of Pará, Brazil.

By Nathan Collins


(Photo: tentenuk/Flickr)

The most obvious way to preserve fragile forest ecosystems is simply to not cut down trees, but preventing deforestation might not be enough to protect biodiversity in tropical forests, according to a study out today in Nature. Less destructive human disturbances, such as selective logging, fires, and clearcutting on adjacent lands may roughly double our impact on some of the most important forests in the world.

In the most stringent circumstances, Brazil mandates that landowners preserve 80 percent of an area’s forest cover, but it isn’t obvious that conserving trees is enough to maintain complex forest ecosystems, writes a team of researchers led by Lancaster University professor Jos Barlow.

Indeed, breaking up forests into increasingly fragmented, isolated sections is thought to drastically reduce biodiversity, and it’s plausible that even subtler actions like selective logging could have an impact. But, Barlow and his colleagues note, no one’s looked for those effects.

Deforestation itself is far from the only thing threatening Brazil’s legendary biodiversity.

The researchers first counted how often they found each of 2,154 plant and animal species in 36 catchments, or river drainage basins, in the Brazilian state of Pará. From that survey, they estimated the conservation value—essentially a measure of species richness—for 371 plots across the 36 catchments.

If only actual deforestation affected biodiversity, then a plot’s conservation value should be proportional to its forest cover—but that’s not what the team found. Instead, plots of land that had seen fires or selective logging and plots adjacent to farms or extensively logged areas suffered substantial biodiversity losses. Forest cover losses of 20 percent, for example, led to between 39 and 54 percent losses in conservation value. In other words, deforestation itself is far from the only thing threatening Brazil’s legendary biodiversity.

“At its most stringent, Brazil’s centrepiece environmental legislation, the Forest Code, mandates Amazonian landowners to maintain 80% of their primary forest cover,” the team writes. “Our results show that even where this level of compliance is achieved, the primary forests of these landscapes may only retain 46–61% of their potential conservation value and are likely to have lost many species of high conservation and functional importance.”