Modelling carbon recovery time after clear-cutting or fire in boreal forests under changing climate

The boreal forest covers approximately 12 million km² and contains one-third of the terrestrial vegetation carbon, making it a vital component of the global carbon cycle. The impact of forest harvesting (e.g. clear-cuts) and forest fires on forest carbon budgets under climate change is still not well understood. This study presents results from simulations with the process-based dynamic global
vegetation model LPJ-GUESS conducted for the boreal forests of Sweden, specifically at Norunda (ICOS) and at a forest in the Ljusdal area (central Sweden). At Norunda, we simulated the clear-cut of a 120-year-old mixed pine-spruce forest and a subsequent set of reforestation approaches. In Ljusdal, where forests were severely affected by wildfire in 2018, we conducted simulations of the forest fire and several post-fire management options with LPJ-GUESS and the fire module SIMFIRE-BLAZE. The model outputs were validated against in-situ observational data (eddy-covariance carbon fluxes, forest characteristics) from the forest stands. Both studies included simulations until the year 2100 following two distinct climate scenarios. We estimated the carbon recovery time using the carbon compensation point (CCP) following clear-cut or forest fire. We found that the CCP for different types of reforestation approaches at Norunda ranged from 12-16 years. For the Ljusdal forest, CPP was reached only 18-33 years following the forest fire and subsequent reforestation strategies, mostly due to carbon-dioxide emissions during the fire. These findings could guide the adoption of suitable reforestation strategies after clear-cutting or wildfires to maximize carbon recovery in boreal forests.