Thanks to Timo Hämeranta for alerting us to the following paper!
Vuichard, N., P. Ciais, L. Belelli, P. Smith, and R. Valentini (2008), Carbon sequestration due to the abandonment of agriculture in the former USSR since 1990, Global Biogeochem. Cycles, 22, GB4018, doi:10.1029/2008GB003212.
The abstract reads
“The end of the Soviet Union and the collapse of its agricultural structures in the early 1990s has induced the abandonment of a large croplands area, which have been recovered by herbaceous plants. This widespread unintended and abrupt land use change took place over 200,000 km2, a large enough scale to impact the continental and global carbon budgets. The goal of this study is to estimate the net biome productivity (NBP) of the abandoned croplands and to assess the soil C storage dynamics due to recent land conversion. The soil C balance and its input (net primary productivity) and output (heterotrophic respiration) fluxes is simulated in a spatially explicit manner with the process-driven natural vegetation/crop model Organizing Carbon and Hydrology in Dynamic Ecosystems-Supra-Thermal Ion Composion Spectrometer prescribed with successive area changes of abandoned croplands during the 1990s. We estimate that regional agricultural abandonment is responsible of a cumulated carbon sink over 1991-2000 of 373 gC m -2, or 64 TgC over the domain considered, which defines a mean annual C sink of 46.7 g C m-2 a1. Agricultural practices during the former cultivation phase determine a legacy on the C sink following abandonment, which impacts by +37% to -25% according to the practice considered (no tillage, no fertilization, and export of some crop residues). We conclude that futures studies of this regional change in the C cycle should better consider management information in order to refine the NBP estimate.”
The conclusion reads
“The simulations presented here indicate that the massive abandonment of croplands in the former USSR in the 1990s has induced a net C sequestration rate of 47 gC m-2 a-1. It is roughly 50% higher than the observed C sequestration rates in the Russian forests for 1961-1998 (~31 gC m-2 a-1 [ Shvidenko and Nilsson, 2003]). Thus, this land use induced net C sequestration rate is significant and leads to a net C sink (NBP) of 64 Tg over 171,000 km2 during the period 1993-2000. However, at the regional scale this sink does not contribute significantly to the carbon balance mainly because the area of the abandoned cultivated lands of former USSR is small (~0.2 106 km2) in comparison for instance of the lands of the Russian forests (~8.8 106 km2). Estimates of the carbon sink of the Russian forests are 268 Tg C a-1 and 272 Tg C a-1 by pool- and flux-based methods respectively [Shvidenko and Nilsson, 2003] while the carbon sink over the abandoned cultivated lands of the former USSR is 8 Tg C a-1. However, the focus should be more on the change in the C balance rather than its absolute value. In this respect, the contribution of the studied land conversion to the regional C balance change over the 1990s is certainly significant.
The main controlling process of NBP in our case study is the large fraction of grass NPP which gets returned to the soil, against only a small fraction of NPP in croplands. This larger return to the soil compensates for the lower NPP of grass ecosystem compared to croplands. Therefore, not surprisingly, our modeled net change in soil C stock is quite sensitive to the agricultural practice applied during the period of cultivation: tillage/fate of straw residues/N fertilizers. According to a set of model sensitivity experiments where each of these practice are turned off, it is the input of N fertilizers which impacts the most the simulated change in soil C storage after abandonment (+37 %). However, in this sensitivity study, we only considered the impact on soil C storage of management practices taken one by one. Combining different practices should lead to a higher range of uncertainty. For instance, considering both reduced export of straw and no tillage should decrease the C gain after abandonment by up to 40 %. Therefore, we strongly recommend that future studies should better represent management information in order to improve the NBP estimate. It will be also interesting to compare for future scenarios, how C gains legated from the agricultural abandonment might be offset by C losses implied by soil warming and faster decomposition.”
Also see the ppt Carbon sequestration due to the abandonment of croplands in the former USSR since 1990.
This is an important paper but it focuses on just the carbon aspect of the climate system. It ignores the very substantial effect of the landscape change on the hydrologic cycle and on the surface energy budget. For effective climate policy, rather than just a “carbon policy” (see), we need to move beyond carbon dioxide as the currency of the cliamte system.
The need to consider the combined effects of landscape change on all aspects of the climate system was emphasized in our papers
Pielke Sr., R.A., G. Marland, R.A. Betts, T.N. Chase, J.L. Eastman, J.O. Niles, D. Niyogi, and S.W. Running, 2003: The influence of land-use change and landscape dynamics on the climate system: Relevance to climate-change policy beyond the radiative effect of greenhouse gases. Chapter 9 in Capturing Carbon and Conserving Biodiversity: The Market Approach, I.R. Swingland, Ed., Earthscan Publications Ltd., London, 157-172.
Marland, G., R.A. Pielke, Sr., M. Apps, R. Avissar, R.A. Betts, K.J. Davis, P.C. Frumhoff, S.T. Jackson, L. Joyce, P. Kauppi, J. Katzenberger, K.G. MacDicken, R. Neilson, J.O. Niles, D. dutta S. Niyogi, R.J. Norby, N. Pena, N. Sampson, and Y. Xue, 2003: The climatic impacts of land surface change and carbon management, and the implications for climate-change mitigation policy. Climate Policy, 3, 149-157.