Carbon cycling under 300 years of land use change: Importance of the secondary vegetation sink

Abstract

[1] We have developed a dynamic land model (LM3V) able to simulate ecosystem dynamics and exchanges of water, energy, and CO 2 between land and atmosphere. LM3V is specifically designed to address the consequences of land use and land management changes including cropland and pasture dynamics, shifting cultivation, logging, fire, and resulting patterns of secondary regrowth. Here we analyze the behavior of LM3V, forced with the output from the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model AM2, observed precipitation data, and four historic scenarios of land use change for 1700-2000. Our analysis suggests a net terrestrial carbon source due to land use activities from 1.1 to 1.3 GtC/a during the 1990s, where the range is due to the difference in the historic cropland distribution. This magnitude is substantially smaller than previous estimates from other models, largely due to our estimates of a secondary vegetation sink of 0.35 to 0.6 GtC/a in the 1990s and decelerating agricultural land clearing since the 1960s. For the 1990s, our estimates for the pastures' carbon flux vary from a source of 0.37 to a sink of 0.15 GtC/a, and for the croplands our model shows a carbon source of 0.6 to 0.9 GtC/a. Our process-based model suggests a smaller net deforestation source than earlier bookkeeping models because it accounts for decelerated net conversion of primary forest to agriculture and for stronger secondary vegetation regrowth in tropical regions. The overall uncertainty is likely to be higher than the range reported here because of uncertainty in the biomass recovery under changing ambient conditions, including atmospheric CO 2 concentration, nutrients availability, and climate.

Harmonization of land-use scenarios for the period 1500–2100: 600 years of global gridded annual land-use transitions, wood harvest, and resulting secondary lands

“…Previous studies have demonstrated the utility of historical gridded land-use-transition estimates for use in regional-global carbon/climate modeling studies Hurtt et al 2002;Roy et al 2003;Shevliakova et al 2009). Land-use transitions not only create important changes to ecosystems (e.g.…”

“…Cumulatively, land-use emissions of carbon to date are comparable to fossil fuel emissions (Houghton 1999). Land-use changes have altered the surface albedo, surface aerodynamic roughness, and rooting depth and terrestrial carbon balance, with resulting effects on regional-global weather, hydrology and climate (Pielke et al 2002;Roy et al 2003;Brovkin et al 2004;D'Almeida et al 2007;Piao et al 2007;Piao et al 2009;Pitman et al 2009;Shevliakova et al 2009;Pongratz et al 2010;Betts et al 2007). Habitat loss is the primary cause of species extinctions (UNEP 2002;Mace et al 2005).…”

“…ED) and global dynamic land models (e.g. LM3V) able to track the consequences of these changes for both the carbon cycle and climate (Hurtt et al 2002;Roy et al 2003;Shevliakova et al 2009). These studies have made use of the detailed land-use transition information to quantify land conversion events and track the resulting demographic effects of land disturbance and recovery, ultimately helping to close regional and global carbon budgets.…”

Potential climate forcing of land use and land cover change

“…Lal (2004) estimates that cultivation has caused the loss of 78 ± 12 PgC from soils since 1850. Modeling studies suggest that LULCC can contribute a net loss of soil carbon globally, from ∼ 13 % of total LULCC carbon emitted (Strassmann et al, 2008) to ∼ 37 % (Shevliakova et al, 2009), or a net gain as in Arora and Boer (2010). Recently, Levis et al (2014) implemented a cultivation parameterization that includes impacts on soil carbon and found an additional global flux of 0.4 PgC yr −1 from soils due to crop management in recent decades.…”

Earth System Model Needs for Including the Interactive Representation of Nitrogen Deposition and Drought Effects on Forested Ecosystems

“…The most common allocation approach assigns C to each plant component (usually leaf, stem, and root) via fixed ratios that vary with plant functional type (PFT), but not spatially or temporally [38,85,88,95,107,[113][114][115]. For models that include N (and less often P), N uptake plays a strong role in governing C assimilation and drives competition between plants and decomposers.…”