Article in Global Change Biology by ACES researchers

Evaluation of climate-related carbon turnover processes in global vegetation models for boreal and temperate forests

Most global vegetation models predict a continued carbon sink in terrestrial ecosystems. However, these models may not correctly account for climate effects on carbon turnover processes, likely leading to underestimation of forest mortality and its feedback to climate change. This is the conclusion of a study published in Global Change Biology (http://onlinelibrary.wiley.com/doi/10.1111/gcb.13660/full), which was led by Martin Thurner and Christian Beer from ACES and Bolin Centre RA4.

Global vegetation models (GVMs) allow us to predict the impact of climate change on the vegetation and thereby triggered feedbacks to climate. The land surface has been acting as a carbon sink, i.e. it sequesters CO2 from the atmosphere, thus mitigating climate change. However, the sustainability of this carbon sink is under debate. Little is known about carbon turnover processes, i.e. processes that lead to the loss of carbon from the vegetation to the soil and atmosphere. Such processes involve the senescence of tree components, known as litterfall, herbivory, mortality of individual trees due to senescence or caused by competition for limited resources, and mortality of forest patches related to extreme events (e.g. drought, fire, insect infestations and other disturbances). It is hardly possible to measure the carbon lost by this variety of carbon turnover processes by inventory studies alone, since these processes act on very different timescales, involving short-term extreme events and long-term responses, and spatial scales, affecting single biomass compartments, individual trees or even whole ecosystems. An evaluation against estimates from satellite remote sensing reveals that for boreal and temperate forests many GVMs show large underestimations in their simulated carbon turnover rate, which result in severe overestimations of modelled compared to observed biomass. This shortcoming likely leads to underestimation of the feedback of changes in forest mortality to climate change. An analysis of spatial gradients identifies a need for improved consideration of frost stress, drought stress and insect outbreak effects on forest mortality in GVMs.

Thurner M, Beer C, Ciais P, Friend AD, Ito A, Kleidon A, Lomas M, Quegan S, Rademacher TT, Schaphoff S, Tum M, Wiltshire A, Carvalhais N (2017) Evaluation of climate-related carbon turnover processes in global vegetation models for boreal and temperate forests. Global Change Biology, Early View, doi:10.1111/gcb.13660.

Comparison of observation-based and simulated (a) mean turnover rate (k), (b) mean net primary production (NPP), and (c) mean biomass in boreal and temperate forests.

Bolin Centre for Climate Research
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