Modelling forest plantations for carbon uptake with the LPJmL dynamic global vegetation model

Abstract

Abstract. We present an extension of the dynamic global vegetation model LPJmL to simulate planted forests intended for C sequestration. We implemented three functional types to simulate plantation trees in temperate, tropical, and boreal climates. The parameters of these functional types were optimized to fit target growth curves (TGCs). These curves represent the evolution of stemwood C over time in typical productive plantations and were derived by combining field observations and LPJmL estimates for equivalent natural forests. While the calibrated model underestimates stemwood C growth rates compared to the TGCs, it represents substantial improvement over using natural forests to represent afforestation. Based on a simulation experiment in which we compared global natural forest versus global forest plantation, we found that forest plantations allow for much larger C uptake rates on the time scale of 100 years, with a maximum difference of a factor 1.9, around 54 years. In subsequent simulations for an ambitious but realistic scenario in which 650 Mha (14 % of global managed land, 4.5 % of global land surface) is converted to forest over 85 years, we found that natural forests take up 37 PgC versus 48 PgC for forest plantations. Comparing these results to estimations of C sequestration required to achieve the 2 °C climate target, we conclude that afforestation can offer a substantial contribution to climate mitigation. Full evaluation of afforestation as a climate change mitigation strategy requires an integrated assessment which considers all relevant aspects, including costs, biodiversity, and trade-offs with other land-use types. Our extended version of LPJmL can contribute such an assessment by providing improved estimates of C uptake rates by forest plantations.

Afforestation for climate change mitigation: Potentials, risks and trade‐offs

“…Previous studies use either a stylized growth curve (Humpenöder et al, ; Kyle et al, ) or natural forest growth from vegetation models (Krause et al, ). Natural forest growth in vegetation models underestimates potential growth rates of trees as no seeding, planting or management is taken into account (Braakhekke et al, ). This study uses forest plantations because if afforestation is actively implemented for the purpose of climate change mitigation it is likely that some form of management is implemented to enhance tree growth.…”

“…Biophysical potential of forest growth on a grid‐basis is modelled using LPJmL (Bondeau et al, ; Sitch et al, ; Figure ). In this study we use the new forest plantation functional types (FPFT) that have been developed to represent planted forests (Braakhekke et al, ). Tree growth is simulated for three FPFTs (temperate, tropical and boreal).…”

“…No forest management after establishment such as irrigation, fertilization or thinning is assumed. The resulting growth rates are substantially higher than natural forest growth rates, but lower than intensively managed forest plantations (see for more info Braakhekke et al, ). Therefore, this representation of forest plantations can be described as a planted forest in line with the FAO definition (FAO, ) with minimal management after establishment.…”