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Browsing by Subject "Yasso"

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  • Holder, Jonathan (2019)
    Forests have acted as a substantial Carbon sink during the last decades. In Finland, forests currently sequester about half of the total anthropogenic CO2 emissions. In order to mitigate climate change, most recent policies, both on the European and the Finnish level, are focussing on increasing forest utilisation, and use forest biomass to substitute fossil resources for material or energy production purposes. However, as increasing harvests commonly reduce the growth potential of forests, their function as a carbon sink could be reduced. This reduction of the forest carbon sink might offset the reduction in emissions gained by substitution. The aim of this study is to analyse how different levels of forest utilisation, i.e. harvest levels, and climate change affect the carbon sink function of Finnish forests at a national level during the period of 2015–2100. In order to quantify these effects in detail, the semi-empirical, climate- and management-sensitive forest growth simulator FORMIT-M is employed to estimate carbon stocks and fluxes in living biomass. The carbon stocks and balances of soils are calculated by applying the Yasso15 soil model to litter input as modelled by FORMIT-M. The carbon balance of harvested wood products is estimated by applying species- and assortment-specific decay functions to harvested timber assortments derived from dimensions. Four harvest scenarios were applied, covering total annual harvest levels between 40 and 87 million m3 a-1, i.e. both reduced and increased levels compared to current levels. The simulations were run for three climate scenarios: current climate (1981-2010 means), and RCP2.6 and RCP8.5 scenarios, the latter two based on predictions of the general circulation model CanESM2. The general findings of the simulations largely confirm earlier research, indicating that higher harvest levels decrease the total C sink. This was true across all climate scenarios examined; in general, the total C sink function of forests was predicted to increase under climate change conditions, with higher C sinks under RCP8.5 than RCP2.6. Under climate change, the relative effect of increasing harvests is reduced, but management in the form of harvest levels remains a more influential factor than climate change. In addition, the reduction in C sink function per unit of additionally harvested C is larger at higher harvest levels, especially under current climate. In the highest harvest scenario, managed forests acted as C sources in the beginning of the modelling period, and the total Finnish forest areas remain net C sinks only due to net C sequestration in preservation areas during this period. The simulations of this study therefore suggest that, from a climate change mitigation perspective, a reduction of harvests is more beneficial than increasing harvests. This is true even when avoided greenhouse gas emissions by replacing fossil resources with forest biomass are considered in the form of a rough estimation of substitution effects. In general, both the absolute magnitude of the C sink and the differences between harvest scenarios are likely to be overestimated in this study, as neither the reduction in growth potential nor the potential reduction of C stocks due to natural disturbances were considered; in addition, potential limiting factors such as nutrient deficiency did not restrict the fertilisation effect of elevated atmospheric CO2 levels. The results include large uncertainties, both regarding the effect and extend of climate change and the potential accumulation of misrepresentations within the growth modelling; hence, the reliability can be expected to decrease during the modelling period. Future applications of the FORMIT-M simulator in Finland should consider the effects of natural disturbances as well as limitations to the substantially improving growing conditions due to climatic conditions and elevated atmospheric CO2 levels; in addition, an optimisation procedure for the distribution of harvests would be beneficial.