De‐eutrophication of a nitrogen‐saturated Scots pine forest by prescribed litter‐raking

Abstract

AbstractShort‐term (<7 years) effects of prescribed litter‐raking on forest‐floor nutrient pools, stand nutrition, and seepage water chemistry were studied in an N‐saturated Scots pine (Pinus sylvestris L.) forest in Southern Germany subject to high atmospheric‐nitrogen deposition. The study was based on a comparison of plots with and without annual prescribed litter raking at three sites with different N‐deposition levels. Prescribed litter‐raking resulted in a considerable reduction of forest‐floor thickness and mass, as well as of forest‐floor C, N, P, K, Mg, and Ca pools. Furthermore, it induced a significant decrease of the foliar N content in current‐year needles of the pines and a more balanced nutritional status of the stand. Particularly on the site subject to the highest N deposition, but to a lesser degree also at the other sites, the mean NO$ _3^- $ concentration in the subsoil seepage water and the N export into the groundwater were substantially reduced on the litter‐raked plots. The results show that in N‐saturated Scots pine ecosystems prescribed litter‐raking on areas of limited size, which are used as sources of groundwater‐derived drinking water and/or serve as habitat for endangered plant species, is a quick and effective method to achieve a more balanced nutritional status of the trees and to reduce seepage‐water NO$ _3^- $ concentrations and N export into the groundwater. In terms of sustainable ecosystem nutrient management, the conversion of conifer monocultures into broadleaf‐rich mixed stands is the better, yet less immediately effective method to reduce the seepage‐water N export from conifer forests subject to high atmospheric‐N deposition.