Impacts of harvesting practices on nutrient balances of forests under high nitrogen deposition

Summary

Forests are essential for providing biomass and timber; however, tree harvesting can pose a risk to forest soils and nutrient stocks. To assess the sustainability of harvest, the nutrient budget approach was used, in which nutrient losses (harvest and leaching should not surpass nutrient inputs (atmospheric deposition and weathering). A large-scale field experiment was established in the Netherlands and the impact of harvest intensity, harvest method and mulching on the nutrient balance was assessed. Key findings show that the nutrient input through atmospheric deposition exceeded national estimates by 2 (for nitrogen) up to 6-fold (for base cations), and that this deposition decreases from extensively to intensively harvested stands. Furthermore, base cation stocks in trees exceed soil base cation stocks indicating a potential risk for nutrient limitation. Moreover, post-harvest leaching strongly increases with increasing harvest intensity resulting in strongly negative post-harvest nutrient balances. Finally, to keep stable or positive nutrient balances it is recommended to use thinnings while final fellings (shelterwood and clearcut) pose risks for long-term site nutrition.