Is there a deforestation limit we can aim for?

Deforestation is bad, according to just about everybody in the world who isn’t actively engaged in cutting down a tree right now. It isn’t a controversial position to say that we should save our rain forests and other major wooded areas, but it also isn’t a particularly useful one. A more interesting question to answer is exactly how much is too much when it comes to deforestation: Just as the world has coalesced around doing our best to hold global warming under two degrees C from preindustrial levels, is there some amount of forest that we really must keep in order to keep the ecosystems at least somewhat intact?

A group of researchers in Ecuador and Germany set out to determine that limit in the tropical Andes region in South America, at least in terms of how forest cover affects “benthic” indicators—essentially measures of how healthy a river or stream is based on the water, sediment, animals living there, and other factors. Specifically, they looked at 23 streams in two separate “headwater catchments” of the Zamora River basin, in Ecuador; one of the two is heavily populated and has been heavily deforested, while the other is a more sparsely populated and less disturbed area. “In Ecuador, deforestation for agriculture and/or urbanization is a critical threat for Andean ecosystems, reaching annual deforestation rates of 2.7 percent between 1989 and 2008 in the montane forests of southern Andes,” they write. So how does that sort of rate change what’s beneath the canopy?

Over the full catchment area, they found that water quality is significantly better when vegetation cover is above 70 percent, giving us one large-scale line it seems good not to cross. That line also holds true for “macroinvertebrate community assemblages,” or groups of animals that would include larval insects, snails, crustaceans, and other such critters; above 70 percent vegetation coverage again, those communities were more diverse. Of 53 genera of macroinvertebrate found in areas with at least 70 percent coverage, an amazing 25 of those were absent from the more deforested areas.

There was some correlation with water quality and macroinvertebrate success at a smaller “riparian” scale, encompassing 30 meters on each side of the stream for its full length, but at an even smaller, local scale the connections broke down.

This is a useful line to know, though of course the specifics may vary based on where in the world one is trying to conserve. And we do need these types of studies in order to define those lines; as it stands, there really isn’t a goal other than to stop pillaging the forests in general. The authors note that in Ecuador in particular, the “constitution defines the right to water and promotes the protection, restoration and management of basins and water resources; but it does not mention how much forest needs to be retained in a catchment or a recommended width for riparian buffers.” Even with the best of intentions, we aren’t sure what we need to save. This is a good—though early—step toward fixing that problem. – Dave Levitan | August 26 2014

Source: Iniguez-Armijos C, Leiva A, Frede HG, et al (2014). Deforestation and benthic indicators: How much vegetation cover is needed to sustain healthy Andean streams? PLoS One, 9 (8) e105869. DOI: 10.1371/journal.pone.0105869

Image: shutterstock.com, Markuso

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