ConservationBytes.com

© A. Hesse

I’ve written rather a lot about rates of forest loss around the world, including accumulated estimates of tropical forest loss and increasing fragmentation/loss in the boreal forest (see Bradshaw et al. 2009 Front Ecol Evol & Bradshaw et al. 2009 Trends Ecol Evol). For the tropics in particular, we used the index that an area of rain forest about the size of Bangladesh (> 15 million hectares) was disappearing each year, and in Russia alone, annual decline in forest area averaged 1.1 million hectares between 1988 and 1993. Mind boggling, really.

But some of these estimates were a bit old, relied on some imprecise satellite data, and didn’t differentiate forest types well. In addition, many have questioned whether the rates are continuing and which countries are being naughty or nice with respect to forest conservation.

It was great therefore when I came across a new paper in PNAS by Hansen & colleagues entitled Quantification of global gross forest cover loss because it answered many of the latter questions.

Part of the problem in assessing worldwide forest cover loss in the past was the expense of satellite imagery, access problems, data storage and processing issues. Happily, new satellite streams and easing of access has rectified many of these limitations. Hansen & colleagues took advantage of data from the MODIS sensor to create a stratification for forest cover loss. They then used the Landsat ETM+ sensor as the primary data for quantifying gross forest cover loss for the entire planet from 2000 to 2005. They defined ‘forest cover’ as “… 25% or greater canopy closure at the Landsat pixel scale (30-m × 30-m spatial resolution) for trees > 5 m in height”.

For your reading pleasure (and conservation horror), the salient features were:

• Russia has the most extensive forest cover, followed by Brazil, Canada and USA
• Estimated area of gross forest cover loss at the global scale is 1,011,000 km², or 3.1 % of year 2000 forest area (0.6% per year from 2000 to 2005)
• Gross forest cover loss was highest in the boreal biome, with fire (increasing mainly due to human-induced fragmentation – Bradshaw et al. 2009 Trends Ecol Evol) accounting for 60 % of that loss (bad Russia!)
• The humid tropics had the second-highest gross forest cover loss, due mainly to broad-scale clearing for agriculture in Brazil, Indonesia and Malaysia (bad Brazil! bad Indonesia! bad Malaysia!)
• Fortunately (?), when expressed as proportion lost from the 2000 extent estimates, the humid tropics is the least disturbed
• The Amazon interior is the largest remaining ‘intact’ forest, followed by the Congo basin
• The dry tropics has the 3^rd-highest gross forest cover loss, with Australia, Brazil, Argentina and Paraguay accounting for most of this (bad Australia et alia!)
• Although the temperate biome had the lowest forest cover (due mainly to forest clearances long, long ago), it had the 2^nd-highest proportional gross forest cover loss
• North America has the greatest area of gross forest cover loss, followed by Asia and South America (bad North America!)
• North America alone accounts for ~ 30 % of global gross forest cover loss, and has the highest proportional gross forest cover loss at 5.1 % (double-bad North America!)
• Brazil has the highest gross national forest cover loss of any nation (bad, bad, bad Brazil!)
• Indonesia and the Democratic Republic of Congo are next in line for tropical countries (bad Indonesia & DRC!)
• USA has the highest proportional global forest cover loss since 2000 (bad America!)
• Despite previous estimates suggesting that Canada has had little forest loss, the new estimates place it second in terms of gross forest cover loss only to Brazil (bad Canada!)

Bottom line? Everyone’s a bastard. We all have a lot of work to do (sigh).

CJA Bradshaw

Hansen, M., Stehman, S., & Potapov, P. (2010). Quantification of global gross forest cover loss Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0912668107