Annika Nordin - Nitrogen Management in Swedish Forests

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In boreal forests, nitrogen supply is a limiting factor for plant growth. Fertilizing with nitrogen can double tree biomass, but may interfere with ecosystem functionality, changing plant species composition and soil microbial communities. The research in my group targets nitrogen effects on ecophysiological mechanisms driving nitrogen-induced ecosystem changes. The aim is to increase our knowledge of both positive and negative effects of nitrogen enrichment on important ecosystem services, such as productivity, carbon sequestration, nitrogen retention and biodiversity. Ultimately, we seek ways to wisely manage nitrogen use in forest ecosystems
Nordin_Annika_portrait

Nitrogen addition to Swedish forests occurs both passively (via deposition of atmospherically transported nitrogen pol- lutants from agriculture, industry and traffic) and actively (via forest fertilization to increase forest yields). The effects of nitrogen addition on forest ecosystems are both positive (increased productivity and carbon sequestration) and nega- tive (water pollution and decreased biodiversity).
My research group studies nitrogen addition effects on forest ecosystems. We have demonstrated that nitrogen addition may shift the balance between plants and herbivorous organisms. This can lead to vegetation changes. For example, nitrogen addition increases disease incidence of pathogenic fungi on bilberry (Vaccinium myrtillus). This causes premature leaf-shed, which results in increased growth of grass competing with the bilberry shrubs. Nitrogen addition also promotes the abundance of winter-moth larvae feeding on the bilberry shrubs. For lingonberry (Vaccinium vitis-idaea) and heather (Cal- luna vulgaris), nitrogen addition increases leaf infection with snow-blight fungi. Hence, when a forest is subjected to elevated nitrogen input, the dwarf-shrubs decline due to increased disease caused by fungal pathogens and increased competition from grasses and herbs.


Forest field-layer dominated by Vaccinium myrtillus L	Vaccinium myrtillus diseased by a fungal leaf pathogen (Valdensia heterodoxa).

Survey of the species composition of forest floor vegetation

Many bryophyte species can be even more sensitive than dwarf-shrubs to nitrogen addition. Particularly sensitive are common forest floor mosses, like stair-step moss (Hylocomium splendens), and many peat-forming mosses (Sphagnum spp). We have studied physiological mechanisms explaining the nitrogen sensitivity of bryophytes. Only in the very long-term (following > 50 years of exposure to continuous high nitrogen input) do mosses have at least a slight capacity to physiologically adjust to high nitrogen input. More often, nitrogen-sensitive bryophytes disappear from ecosystems subjected to high nitrogen input. These studies show that nitrogen addition to a forest may have negative effects on forest biodiversity by decreasing the abundance of important keystone species. Ecosystem functionality can also be affected, since forest understory species composition influences ecosystem carbon sequestration, as well as nitrogen retention. Moreover, nitrogen effects can be very long-lasting. We have demonstrated effects on understory vegetation species composition of forest fertilization in the forest generation following the one fertilized (> 20 years after the fertilization). The effects include increased abundance of nitrogen-favoured grasses and herbs, and decreased (ca. 40 %) abundance of dwarf-shrubs.
Are there ways we can use nitrogen to increase forest yields while avoiding negative effects on forest biodiversity and ecosystem functionality? We think so. Our idea is to find alternative fertilizers and methods of applying fertilizers that cause less severe and long-lasting effects on forest biodiversity, while inducing stronger tree growth responses greaterthan current practices for forest fertilization.

Svensk sammanfattning

Key publications

Wiedermann MM, Gunnarsson U, Ericsson L, Nordin A 2009. Ecophysiological adjustment of two Sphagnum species in response to anthropogenic N deposition. New Phytologist 181: 208 – 217.

Strengbom J, Nordin A 2008. Commercial forest fertilization cause long-term residual effects in ground vegetation of boreal forests. Forest, Ecology & Management 256: 2175 – 2181.

Wiedermann MM, Nordin A, Gunnarsson U, Nilsson MB, Ericson L 2007. Global change shifts vegetation and plant-parasite interactions in a boreal mire. Ecology 88: 454 – 464.

Forsum Å, Dahlman L, Näsholm T, Nordin A 2006. Nitrogen utilization by Hylocomium splendens in a boreal forest fertilization experiment. Functional Ecology 20: 421 – 426.

Nordin A, Strengbom J, Witzell J, Näsholm T, Ericson L 2005. Nitrogen deposition and the biodiversity of boreal forests – implications for the nitrogen critical load. Ambio 34: 20 – 24

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July 2010

Friday, July 30, 2010
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