Tamm Review: Influence of forest management activities on soil organic carbon stocks: A knowledge synthesis

•Afforestation of former croplands increases soil C stocks, but stocks are unchanged or reduced in former grasslands and peatlands.•Removal of biomass through harvesting, herbivory or removal of residue or fuelwood reduce soil C stocks, in accordance with the intensity of removal.•Nitrogen addition through fertilization or inclusion of N-fixing plants consistently increases soil C stocks across a wide range of forest ecosystems.•Tree species identity has a stronger impact on soil C stocks than tree species diversity.•Stand density management and thinning have small effects on forest soil C stocks.•Additional long-term field experiments are needed, particularly in ecosystems other than north-temperate and boreal forests. Almost half of the total organic carbon (C) in terrestrial ecosystems is stored in forest soils. By altering rates of input or release of C from soils, forest management activities can influence soil C stocks in forests. In this review, we synthesize current evidence regarding the influences of 13 common forest management practices on forest soil C stocks. Afforestation of former croplands generally increases soil C stocks, whereas on former grasslands and peatlands, soil C stocks are unchanged or even reduced following afforestation. The conversion of primary forests to secondary forests generally reduces soil C stocks, particularly if the land is converted to an agricultural land-use prior to reforestation. Harvesting, particularly clear-cut harvesting, generally results in a reduction in soil C stocks, particularly in the forest floor and upper mineral soil. Removal of residues by harvesting whole-trees and stumps negatively affects soil C stocks. Soil disturbance from site preparation decreases soil C stocks, particularly in the organic top soil, however improved growth of tree seedlings may outweigh soil C losses over a rotation. Nitrogen (N) addition has an overall positive effect on soil C stocks across a wide range of forest ecosystems. Likewise, higher stocks and faster accumulation of soil C occur under tree species with N-fixing associates. Stocks and accumulation rates of soil C also differ under different tree species, with coniferous species accumulating more C in the forest floor and broadleaved species tending to store more C in the mineral soil. There is some evidence that increased tree species diversity could positively affect soil C stocks in temperate and subtropical forests, but tree species identity, particularly N-fi