The Environmental Legacy of Modern Tropical Deforestation

Abstract

Tropical deforestation has caused a significant share of carbon emissions and species losses, but historical patterns have rarely been explicitly considered when estimating these impacts [1]. A deforestation event today leads to a time-delayed future release of carbon, from the eventual decay either of forest products or of slash left at the site [2]. Similarly, deforestation often does not result in the immediate loss of species, and communities may exhibit a process of "relaxation" to their new equilibrium over time [3]. We used a spatially explicit land cover change model [4] to reconstruct the annual rates and spatial patterns of tropical deforestation that occurred between 1950 and 2009 in the Amazon, in the Congo Basin, and across Southeast Asia. Using these patterns, we estimated the resulting gross vegetation carbon emissions [2, 5] and species losses over time [6]. Importantly, we accounted for the time lags inherent in both the release of carbon and the extinction of species. We show that even if deforestation had completely halted in 2010, time lags ensured there would still be a carbon emissions debt of at least 8.6 petagrams, equivalent to 5-10 years of global deforestation, and an extinction debt of more than 140 bird, mammal, and amphibian forest-specific species, which if paid, would increase the number of 20(th)-century extinctions in these groups by 120%. Given the magnitude of these debts, commitments to reduce emissions and biodiversity loss are unlikely to be realized without specific actions that directly address this damaging environmental legacy.

Keywords: carbon debt; species extinction debt; time lags; tropical deforestation.

Figure 1

Modeled Annual Deforestation Rates from 1950 to 2009 in Five-Year Intervals Rates are shown in km²/year. Error bars represent 95% confidence interval estimate from 100 model replicates. See also Figure S1 and Table S1.

Figure 2

Vegetation Carbon Emissions and Species Losses from the Deforestation of Tropical Forests from 1950 to 2009 (A) Vegetation carbon emissions, separated into those that occurred from deforestation that took place in that year (immediate) versus those that occurred as a result of time lags in the release of carbon from deforestation in previous years (committed). (B) Species losses, separated into those that have already occurred (loss) and those that will occur as a result of time delays in the extinction of species (debt). Error bars represent 95% confidence intervals from 100 model replicates. Figures for the Amazon, the Congo Basin, and SE Asia are presented in Figures S2 and S3.

Figure 3

Magnitude of Carbon Emissions and Extinction Debts in the World’s Tropical Forests in 2009 (A) and (B) show results for the Congo Basin, (C) and (D) for the Amazon, and (E) and (F) for SE Asia. See also Table S2. (A, C, and E) Carbon emissions. Maps display the (log-normal transformed) median carbon tons per hectare left to decay after 2009. (B, D, and F) Extinction debts. Maps show the (log-normal transformed) median number of forest-specific species committed to extinction as of 2009 due to past tropical deforestation.

Figure 4

Linear Regression between Carbon and Extinction Debts in the World’s Tropical Forests in 2009 Each gray dot represents a 100 km² pixel. The carbon debt was aggregated from its initial 1 km² resolution to match the resolution of the extinction debt. Figures for the Amazon, the Congo Basin, and SE Asia are presented in Figure S4.