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Subprogram C2: Nitrogen Induced Ecosystem Changes  
Effects of Nitrogen Deposition in Forest Ecosystems on Ground-layer Species Dynamics  
The goal is to use ground-layer species composition in deciduous, hardwood forests in Sweden as a dynamic measure in time and space of the response of forest ecosystems to nitrogen deposition. A dose-response function is established by relating observed vegetation changes to various nitrogen measures.

These are present nitrogen deposition, accumulated nitrogen deposition and nitrogen deposition relative to nitrogen mineralisation rates in the soil. Effects of soil eutrophication and acidification on vegetation are considered separately as far as possible. The work is based on 700 deciduous forest sites in the South part of Sweden.

Important activities are:

· Data on nitrogen mineralisation rate, current and accumulated nitrogen deposition and nitrate deposition is used to calculate the varying dose-responses of ecosystems and their critical loads at defined changes in the vegetation.

· New plant functional types are defined, related to soil eutrophication and validated towards long-term changes in ground vegetation.

· The uptake of nitrate by the ground flora is measured to estimate to what extent it prevents nitrate leaching in soils.

· A simple model is parameterised for soil chemistry using the above parameters.

Ursula Falkengren-Grerup
Lund University
ursula.falkengren-grerup@planteco.lu.se