Effect of future forest management on carbon and energy budgets in pine forests on mineral soil in southern Finland

Abstract. In forest management, carbon sequestration is often the main topic of interest when it comes to climate change mitigation. Here, we examined other climate impacts of forests – caused by changes in albedo, latent heat flux and sensible heat flux – and assessed their significance in relation to carbon sequestration in Finnish pine forests growing on mineral soil. Three different forest management scenarios with different harvest intensities were modelled with JSBACH_FOM forced with data from three climate models CanESM2, MIROC5 and CNRM-CM5 under two climate scenarios RCP 4.5 and RCP 8.5 from 2010 to 2054. Forest management scenarios were compared with each other, and the differences in the 45–year mean energy balance, connected to the relevant climate impacts, were converted from W m^-2 to carbon equivalent with time-dependent-emission-equivalent (TDEE) metric. Based on our findings, carbon sequestration acts as the main driver behind the differences between the harvest scenarios in their total climate impact. Carbon sequestration was highest in the scenario with the lowest harvest intensity, and lowest in the scenario with the highest harvest intensity. The total carbon pool of the forest experienced growth in all of the harvest scenarios. The lowest harvest intensity yielded the highest carbon sequestration, but resulted in the highest absorption of solar radiation due to the low albedo, which slightly decreased the benefit from the carbon sequestration. The albedo–induced carbon equivalent climate impact differences between the harvest scenarios were in the range of 4–7 % of the differences in carbon sequestration. The carbon equivalent differences from fluxes of latent and sensible heat between the harvest scenarios were in the range of 3–5 % in comparison to the differences in carbon sequestration, with an opposite sign in relation to the differences from the albedo–induced climate impact. Accounting for the carbon equivalent climate impacts did not result in any of the scenarios becoming a carbon source, indicating that the forests remained beneficial in terms of climate change mitigation despite the management actions analyzed in this study. The harvest scenario with lowest harvest intensity resulted in the most beneficial carbon equivalent climate impact in terms of climate change mitigation. After accounting for the differences in albedo and fluxes of latent and sensible heat in the total carbon equivalent climate impact between the scenarios, the climate change mitigation benefit resulting from the harvest scenarios with higher carbon sequestration was reduced in total by less than 5 % across all harvest and climate scenarios. No significant differences were found between RCP 4.5 and RCP 8.5 in the climate impact differences from the different sources between the harvest scenarios.