Mountain forests store 40 percent more carbon than expected

It’s not easy to measure carbon in mountain forest ecosystems. For one thing, climbing into these forests can be difficult, exhausting, and even treacherous. For another, many mountain rainforests are almost constantly blanketed by clouds—hence the term “cloud forest”—making it problematic to measure above-ground carbon storage from the air or satellite. But a new review study in Biogeosciences found that many estimates of carbon storage in montane tropical forests have been largely underestimated.

“Tropical mountain forests are under heavy human pressure and are experiencing rapid rates of deforestation and degradation. It is well known that tropical mountain forests are biodiversity hotspots as well as playing an important role in downstream water resources. Our study demonstrates that tropical mountain forests are also globally important stores of carbon, providing more justification to protect these forests,” lead author Dominick Spracklen with the University of Leeds told mongabay.com.

Cloud forest in Indonesia New Guinea. Photo by: Rhett A. Butler.

Looking at over 90 studies of above-ground carbon in mountain forests, Spracklen and co-author Renton Righelato with the University of Reading, found that the angle of the forest’s slope has led to many erroneous carbon storage estimates.

“The angle of the slope means that the actual land-surface area of a hillside is greater than the planimetric area that is recorded by a map…On shallow slopes this makes little difference, but on the steep slopes found in mountain forests the land-surface area of mountain forests is actually a lot more than seen on a map,” explained Spracklen.

In fact, the scientists found that 75 percent of tropical forests on mountain sides rested on steep slopes, meaning that carbon storage in these ecosystems is 40 percent more than usually calculated worldwide.

Still, above-ground carbon in tropical montane forests remains less than in lowland rainforests by land area, but not by too much.

“We found that the difference is less than you might expect. In the Andes, mountain forests store only about 20 percent less above-ground carbon per land-surface area than lowland forests,” said Spracklen adding, “We don’t yet know the reason behind the differences. Some researchers are probing into how carbon fluxes change along altitude gradients, and these studies promise to tell us more about how and why changes occur.”

Moreover, the current research only looked at above-ground biomass and not the carbon sequestered in the soil. Spracklen says this area “needs more research.” In addition, studies of above-ground carbon in tropical montane forests have largely focused on the Andes with few studies in Africa or Asia. But still, the results show montane forests are likely a much more important carbon sink than expected.

“Hopefully our study will inspire forest carbon projects in the mountains,” Spracklen noted.

Forest cleared around hill for cattle ranching in Colombia. More-and-more montane forests are facing clearing. Photo by: Rhett A. Butler.

Citations:

Spracklen, D. V. and Righelato, R.: Tropical montane forests are a larger than expected global carbon store, Biogeosciences, 11, 2741-2754, doi:10.5194/bg-11-2741-2014, 2014.

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