Rainforests on Fire

   
In his 2003 article, Fire Science for Rainforests, Mark A. Cochrane explains that while tropical forest fires have never been unprecedented, the problem is the frequency with which they are nowadays being burned. Fires in tropical forests have return intervals of hundreds or even thousands of years. As a result, tropical rainforest are evolutionarily not adapted to current patterns of fires, with thin barks that provide little protection even against low intensity fires.

Most fires in tropical rainforests are associated with forest edges and are mostly arise from ‘slash and burn’ practices getting out of control. Forest edges, borders of forested and deforested land, generally have increased mortality of trees, decreased living biomass and increased fuel loads (dry wood debris), which makes these forests susceptible to fire. While due to their high sub-canopy humidity extensive undamaged forests make large forest fires almost impossible, current levels of fragmentation in tropical forests (with scattered deforested areas) make large areas of forestland threatened. In addition, extensive selective logging (when only certain trees are removed but in large numbers) significantly decreases forest biomass and can thus also increase fire susceptibility.

Cochrane points out that frequent tropical forest fires lead to a vicious cycle where forests thinned by fire transpire less water, which leads to lower humidity and as a result increased future fire probability. Instead of applying fire knowledge from other parts of the world, Cochrane says, to prevent the continuous loss of large areas of tropical forests “current fire knowledge needs to be interpreted in the context of tropical forests and, where necessary, added to, by defining the mechanisms by which fire and ecosystem processes interact in these forests."

Photo: Daniel Beltra,
www.danielbeltra.com