VDI 3959 Blatt 1:2008-12 (R2017)

Nitrogen availability (nitrogen is abbreviated as 'N' in the following text) is one of the principal habitat factors determining the functions and the species composition of vegetation. The evaluation of N-indicator values of plant species is particularly suitable for detection of eutrophication in forest ecosystems, because in forests particularly large amounts of N are deposited from the air owing to the pronounced aerodynamic roughness, N availability is not purposely controlled by fertilisation apart from compensatory liming, the ground vegetation is not purposely controlled by sowing, planting, mowing, grazing, or use of plant protection agents, and disturbances due to harvesting and passage of vehicles are comparatively rare. The method is suitable for the detection of spatial gradients and temporal changes in N supply, e. g. within the framework of environmental observation programmes such as the German federal forest inventory, soil survey, or ecological area sampling.