Canopy openness rather than tree species determines atmospheric deposition into forests

Summary

Atmospheric nutrient deposition plays a crucial role in supplying nutrients to forests on poor soils, making it a key factor in maintaining nutrient stocks and forest productivity. We compared total atmospheric deposition in production forests of European beech (Fagus sylvatica), Douglas fir (Pseudotsuga menziesii), and Scots pine (Pinus sylvestris) by measuring bulk deposition and throughfall while accounting for canopy exchange. We assessed the differences in total deposition resulting from forest management practices such as high-thinning, shelterwood and clearcutting, on forest structure for both macronutrients and micronutrients in areas exposed to high nutrient deposition. We demonstrate that total nutrient deposition is highest in Douglas fir stands and lowest in Scots pine stands, primarily due to differences in dry deposition. The total deposition in forest exceeds national estimates because nutrient deposition in forests was higher than expected compared to more open areas. Canopy openness strongly influences the total deposition of all nutrients except phosphorus (P). Total deposition increases by a factor of 2.2 when moving from clearcuts to closed forests, with the extent of the increase varying among tree species and nutrients. Additionally, total deposition fluctuates between seasons, revealing clear seasonal patterns in both throughfall and canopy exchange. Our results suggest that the effective capture of potentially growth-limiting nutrients (such as K, Ca, Mg and Mn) in closed and thinned production forests significantly contributes to the resilience of forests on nutrient-poor, acidified soils. Our results underscore the importance of considering the effects of harvest intensity on canopy openness and forest structure and, to a lesser extent, tree species when calculating nutrient inputs from atmospheric deposition.