Wednesday, May 5, 2010

Gross forest cover loss

We are mostly aware of deforestation occurring in third world countries. Which is exactly why I must convey the findings of a particularly illuminating paper, Quantification of global gross forest cover loss, by Matthew Hansen, Stephen Stehman, and Peter Potapov of South Dakota State University and State University of New York (SUNY), published in Proceedings of the National Academy of Sciences (April 2010).

The researchers used satellite imagery to quantify the Gross Forest Cover Loss, GFCL, defined as ‘the area of forest cover removed because of any disturbance, including both natural and human-induced causes’ from 2000 to 2005 (‘forest cover’ is specified as 25% (or greater) of canopy closure for trees over 5 metres tall).

To summarise the findings:
Firstly, during this time period, 3% (1011,000 km2 ) of the world’s forest disappeared, which relates as a loss of 3.1% from the estimated total forested area in 2000 (32688,000 km2).

Secondly, amongst the biomes, the
boreal experienced the largest GFCL (where 60% was due to fire), followed by the humid tropical (mostly due to clearing for agriculture and plantations, especially in Brazil, Indonesia, and Malaysia), dry tropical (again, due to clearing for agriculture, and mostly in Australia, Brazil, Argentina, and Paraguay), and temperate biomes.

Thirdly, amongst the continents, North America had the greatest GFCL (around 30%), followed by Asia and South America. Interestingly, Africa exhibited the least GFCL.

Fourthly, amongst the seven countries which has over 100,000 km2 of forests (Russia, Brazil, US, Canada, China, Indonesia, and Congo), Brazil showed the largest GFCL (165,000 km2; of which 26000 km2 were rainforests and 7000 km2 were dry tropical forests) followed by Canada (160,000 km2).

Fifthly, the greatest proportional GFCL was exhibited by US, which lost more than 120,000 km2 (6% of its forest cover in 2000) mainly due to logging. Canada’s proportional forest loss was 5.2% of its forest cover, higher than Brazil’s. Of the remainder, Indonesia lost 3.6%, Russia lost 2.8%, China lost 2.3%, and DRC lost 0.6% of their respective forest covers.

There are some caveats with this otherwise illuminating study: it did not factor in forest gains during this time period. Secondly, the study period is from 2000-2005, and obviously is not indicative of what happened over the past half decade. It is also limited by its definition of forest cover. Yet, it does serve to remove some amount of misconceptions!
Hansen, M., Stehman, S., & Potapov, P. (2010). From the Cover: Quantification of global gross forest cover loss Proceedings of the National Academy of Sciences, 107 (19), 8650-8655 DOI: 10.1073/pnas.0912668107

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