Climate-regulation services of natural and agricultural ecoregions of the Americas

Abstract

Terrestrial ecosystems regulate climate through both biogeochemical (greenhouse-gas regulation) and biophysical (regulation of water and energy) mechanisms 1,2 . However, policies aimed at climate protection through land management, including REDD+ (where REDD is Reducing Emissions from Deforestation and Forest Degradation) 3 and bioenergy sustainability standards 4 , account only for biogeochemical mechanisms. By ignoring biophysical processes, which sometimes offset biogeochemical effects 5,6 , policies risk promoting suboptimal solutions 1,2,4,7-10 . Here, we quantify how biogeochemical 11 and biophysical processes combine to shape the climate regulation values of 18 natural and agricultural ecoregions across the Americas. Natural ecosystems generally had higher climate regulation values than agroecosystems, largely driven by differences in biogeochemical services. Biophysical contributions ranged from minimal to dominant. They were highly variable in space, and their relative importance varied with the spatio-temporal scale of analysis. Our findings reinforce the importance of protecting tropical forests 7,10,12,13 , show that northern forests have a relatively small net effect on climate 5,10,13 , and indicate that climatic effects of bioenergy production may be more positive when biophysical processes are considered 14,15 . Ensuring effective climate protection through land management requires consideration of combined biogeochemical and biophysical processes 7,8 . Our climate regulation value index serves as one potential approach to quantify the full climate services of terrestrial ecosystems.Anthropogenic land use has been, and will continue to be, a major driver of the climate system 6,[16][17][18] . In terms of biogeochemical drivers, land-use change and agriculture together account for over 25% of global greenhouse-gas (GHG) emissions 19 . From 1990 to 2007, gross CO 2 emissions from tropical deforestation were equal to ∼40% of global fossil fuel emissions 18 . In recent years, agriculture has contributed ∼14% of total global GHG emissions 19,20 .Terrestrial ecosystems also strongly affect climate through their control over albedo and evapotransipiration 5,6,8,16,21,22 . Vegetated surfaces-especially forests-typically have lower albedos than bare ground and therefore absorb more incoming solar radiation. The reduction in net radiation (R n ) associated with deforestation has a cooling effect on the climate 5,22,23 -sometimes even outweighing GHG-induced warming 5,18 . Counteracting this, clearing vegetation reduces evapotranspiration and associated latent heat flux (LE). Without the vegetation, energy normally used to evaporate water instead heats the land surface 6,8,14,22,23 . Understanding the counteracting effects of R n and LE is key to quantifying the climate regulation values (CRVs) of different ecosystems 1 .Policies that affect land use may serve as one effective strategy contributing to climate change mitigation 2,12 or may inadvertently exacerbate the problem 24 . Major national and intern...

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