Tuesday, May 4, 2010

Under Cover

While working on my masters thesis I got really interested in the rates of forest and species loss. As a result, articles relating to these topics still catch my eye. So when I saw this article published online in PNAS I knew I couldn't pass it up.

If you are reading this blog then you are probably aware of the massive forest loss in the topics and other places around the world. Forests that aren't completely cut down are fragmented into ever smaller islands and refugia. We can see this happening, but putting a rate to it can be difficult. Typically, rates are calculated by such methods as putting together a large meta-analysis or collecting lots of satellite images. This study does the latter in that the researchers took data from the MODIS sensor to look at stratification for forest cover loss. MODIS (Moderate Resolution Imaging Spectroradiometer) is an instrument aboard the Terra (EOS AM) and Aqua (EOS PM) satellites that orbit around the Earth. Terra passes from north to south across the equator in the morning, and Aqua passes in the afternoon. This allows the satellites to view the entire surface of the Earth every 1-2 days. The authors also used the Landsat ETM+ to quantify gross forest cover loss (GFCL) for the entire planet. With these data they were able to compare GFCL among biomes, continents, and countries. Note that "GFCL is defined as the area of forest cover removed because of any disturbance, including both natural and human-induced causes."

"GFCL was estimated to be 1,011,000 km2 from 2000 to 2005, representing 3.1% (0.6% per year) of the year 2000 estimated total forest area of 32,688,000 km2." The results showed that Russia had the most extensive forest loss. Next in line were Brazil, Canada and the USA. If you break it down by type then you see the most loss in boreal forests, Russia being the biggest offender again - 60% of boreal forest loss can be blamed on them. Tsk tsk. Humid tropical forests rank next, especially in the countries of Brazil, Indonesia and Malaysia. Although, in terms of smallest proportion lost they actually rank pretty well. Mweh, still not exactly a comforting figure. Sticking with the tropics, dry tropical forests rank next, especially in the countries of Australia, Brazil, Argentina and Paraguay. Temperate forests have been hacked at for hundreds of years and, as of this study, still managed to have the second higest proportional loss (after boreal forests, which I mentioned above), with North America being the biggest offender -- 30% of the blame for global loss (5.1% proportional loss) lies there. Also, I would be remiss if I did not mention that the processes driving GFCL, and rates of recovery from it, vary regionally. If you look at the boreal system you will find that naturally induced fire is important, and in other systems additonal factors are key. But all in all, everybody needs to step back -- to a global scale, as in the picture at the top -- and see what this fragmentation is doing to these regions. (insert finger waggle and head shaking here)

Here's the article:
Hansen, M.C., S.V. Stehman, and P.V. Potapov (2010) Quantification of global gross forest cover loss. Proceedings of the National Academy of Sciences: published online. (DOI: 10.1073/pnas.0912668107)

(Both images are credited to NASA's MODIS website: http://modis.gsfc.nasa.gov/gallery/ and more spectactular images can be found there. Check it out!)
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