Chapter 15: Forest remediation options in the face of excess nitrogen deposition
Although nitrogen (N) deposition has decreased in Europe and the United States for decades, considerable areas of the world will likely continue to receive high levels of N deposition in the future. Some soil chemical variables can respond quickly to declining N deposition, but many other ecological effects persist for a long time. Forest management options are needed to mitigate negative effects of excess N deposition and/or promote ecosystem recovery under declining N deposition. Based on a literature review, this chapter i) summarizes the negative effects of excess N deposition on soil chemistry and plant community to identify the key detrimental effects in need of remediation, ii) synthesizes the ecosystem responses to declining N deposition to identify key processes for intervention need, and iii) proposes specific management approaches to remediate the effects of excess N deposition and/or promote ecosystem recovery. Soil N eutrophication, soil acidification, plant diversity loss and forest growth decline are identified as four key negative impacts of excess N deposition. Potential remediation approaches are proposed for each negative impact, including i) carbon additions and biomass removal for N eutrophication, ii) liming and wood ash addition for soil acidification, iii) liming, adding deficient nutrients, replenishing seed banks and replanting target species for biodiversity loss, and iv) liming, adding deficient nutrients and replanting tolerant tree species for forest growth decline. Future research efforts are needed to design a combination of the abovementioned approaches to improve the effectiveness and avoid intended effects.