The land carbon sink of Lithuanian forests in the light of climate change: A model approach

Sammanfattning: Forests form the backbone of the European terrestrial carbon sink (State Forest Service & Ministry of Environment, 2018). As the European Union (EU) strives to become climate neutral by 2050, forests are accounted for the natural carbon absorption mechanism (European Commission, n.d.). Currently, the European net land carbon sink is decreasing largely due to forest ageing (Pilli et al., 2022), and increasing soil carbon emissions (Morales et al., 2007). Lithuania, a country composed of temperate-boreal forests located by the Baltic Sea, is witnessing a similar trend. Whilst Lithuania has demonstrated vast carbon sequestration rates over the past decades, the forest ecosystem, primarily composed of Norway spruce, Scot’s pine and Silver birch, is becoming a carbon emitter (Ministry of Environment, n.d.; Mozgeris et al., 2021). To come in line with the targets set by the EU, Lithuania aims to expand its woodlands. With that, appropriate silviculture management practices could support higher carbon sequestration rates. The scope of this study is to explore the behaviour of the three most common tree species and a so-called Natural stand in Lithuania, using a dynamic vegetation model LPJ-GUESS. For the first time the model has been applied solely in Lithuania. Following a baseline climate along with two Representative Concentration Pathway scenarios, RCP2.6 and RCP8.5, three major research questions were addressed: [i] the general response to climate change; [ii] species response to climate change; [iii] response to forestry management strategies. Regarding [i] by 2100 a majority of forests become carbon emitters, due to a higher net soil carbon release compared to carbon uptake by forests. With respect to [ii] broadleaf species were more favoured, whilst needleleaf trees did not exhibit particular sensitivities to the changes in simulated abiotic factors. Concerning [iii] both monoculture and silviculture plantations yielded similar carbon absorption rates due to the dominance of birch. The modelled LPJ-GUESS results demonstrated that two of the three most common species in Lithuania, would not naturally grow at this specific ecoclimate. As a take home message, in order to improve forest land sinks, Lithuania and Europe as a whole, should consider mixed-age and mixed-species plantations in forestry management with a preference for native broadleaf trees in central Europe. Additionally, forests should be allowed to undergo successional development, with the avoidance of clearcuts. Eventually, since the net carbon sink of European forests altogether is weakening, all member states must be prepared to take supplementary initiatives in reducing GHG emissions as part of climate change mitigation.