Of prime importance is to understand to what extent vegetation effects due to increased nitrogen deposition are scale-dependent. The studies have been able to quantify a drastic increase in the abundance of natural enemies already at low levels of nitrogen supply and preliminary data indicates that these attacks have a measurable impact on species composition. This indicates that the interaction between parasitic fungi, herbivorous insects and vegetation is an important factor regulating species assemblage in coniferous forests.

The studies comprises:

· Additions of different doses of nitrogen in experiments with plot sizes between 1 and 5000 m2.

· Identification of simple indicators that can be used in assessments of the risk for significant effects on species composition in ecosystems subject to nitrogen deposition.

· Development of new concepts of critical load and environmental monitoring (together with other activities of ASTA).

Lars Ericson
Umeå University
lars.ericson@eg.umu.se