Determination of tropical deforestation rates and related carbon losses from 1990 to 2010

Abstract

We estimate changes in forest cover (deforestation and forest regrowth) in the tropics for the two last decades (1990-2000 and 2000-2010) based on a sample of 4000 units of 10 ×10 km size. Forest cover is interpreted from satellite imagery at 30 × 30 m resolution. Forest cover changes are then combined with pan-tropical biomass maps to estimate carbon losses. We show that there was a gross loss of tropical forests of 8.0 million ha yr(-1) in the 1990s and 7.6 million ha yr(-1) in the 2000s (0.49% annual rate), with no statistically significant difference. Humid forests account for 64% of the total forest cover in 2010 and 54% of the net forest loss during second study decade. Losses of forest cover and Other Wooded Land (OWL) cover result in estimates of carbon losses which are similar for 1990s and 2000s at 887 MtC yr(-1) (range: 646-1238) and 880 MtC yr(-1) (range: 602-1237) respectively, with humid regions contributing two-thirds. The estimates of forest area changes have small statistical standard errors due to large sample size. We also reduce uncertainties of previous estimates of carbon losses and removals. Our estimates of forest area change are significantly lower as compared to national survey data. We reconcile recent low estimates of carbon emissions from tropical deforestation for early 2000s and show that carbon loss rates did not change between the two last decades. Carbon losses from deforestation represent circa 10% of Carbon emissions from fossil fuel combustion and cement production during the last decade (2000-2010). Our estimates of annual removals of carbon from forest regrowth at 115 MtC yr(-1) (range: 61-168) and 97 MtC yr(-1) (53-141) for the 1990s and 2000s respectively are five to fifteen times lower than earlier published estimates.

Keywords: carbon emissions from tropical deforestation; carbon removals from tropical forest regrowth; climate change impacts; forest cover changes in tropics for the 1990s and the 2000s; spatial explicit use of pan tropical biomass maps combined with detailed deforestation maps.

Fig 1

Proportions of forest cover within all sample sites over the tree continents for year 2010.

Fig 2

Losses of forest cover and other wooded land for all sample sites over the tree continents and the two periods: 1990–2000 and 2000–2010. Gross loss of forest cover appears in orange circles when gross loss from other woodland losses appears in yellow circles. Range is 0–100% loss over one decade.

Fig 3

Gross carbon losses from forest cover and Other Wooded Land (OWL) losses for all sample sites over the tree continents and the two decades: 1990–2000 and 2000–2010 (3 × 2 panels). Red color means that 100% of carbon losses are due to forest losses when blue color mean than 100% of carbon losses are due to OWL losses.

Fig 4

Continental charts showing (from left to right): (a) area of forest cover (green) and other wooded land (orange) for year 2010 in million ha, (b) annual gross loss of forest cover for 1990s (pink) and 2000s (red) in million ha yr⁻¹ and (c) annual gross loss of carbon losses from changes in forest cover and other wooded land for 1990s (light blue) and 2000s (dark blue) with removals from forest regrowth (yellow) in million tC yr⁻¹. Ranges represent statistical standard error for (a) and (b) and maximum–minimum estimates for (c).