Nitrogen availability and ground vegetation dynamics. Role of anthropogenic and natural factors?

Rationale

Hemispherical photograph in a forest stand

Ground vegetation is a powerful bio-indicator of the environment. As such it has been widely used to establish forest types. More recently, it has been used to detect changes in the environment which may be ascribed to human activities (air pollution and in particular nitrogen deposition, climate change). The advantage of such vegetation studies lies in their lower cost in comparison with the measurement of the causal factors (e.g. air chemistry) or the response factors (e.g. soil chemistry). However, the results of vegetation studies are difficult to interpret. Ground vegetation often reflects a combination of ecological factors rather than a single one, or it may react identically to different factors. This is especially the case for vegetation changes indicating improved nitrogen availability.

Project aims

The project aims at discriminating the various factors which may influence the spatial and temporal dynamics of ground vegetation. Emphasis is being given to the role of nitrogen.

Methods

The project uses the data from vegetation assessment carried out in the project "Biogeochemical cycling and ground vegetation". The vegetation is surveyed at three levels of intensity:

• Establishment of a complete list of the vascular plants and byophytes present in the whole plot.
• Assessment of the vegetation (tree, shrub, herb and moss layer) on three concentric circular plots (30 m², 200 m² and 500 m²) using the Braun-Blanquet scale.
• Detailed assessment of the vegetation on 16 permanent quadrats (1 m²), estimating the percentage cover of each species.

The vegetation assessment are carried out every second year, in summer and, for sites with a distinct vernal flora, also in spring. The data on soil, nutrient fluxes, climate, stand history collected in the other LWF projects will contribute to the interpretation of the spatial and temporal dynamics of ground vegetation. In addition to these measurements, potential light conditions are assessed with hemispherical photographs of the canopy above the permanent quadrats and the Leaf Area Index (LAI) is estimated with an LAI-2000 Plant Canopy Analyzer (Li-cor, Inc., Lincoln, NE).

Participants

• Walter Keller
• Peter Kull
• Anne Thimonier (Project leader)
• Jean-Luc Dupouey (INRA Nancy, France)
• Susanne Ilg
• Fabienne Progin
• Caroline Stein
• Norbert Kräuchi

Contact

• Anne Thimonier Rickenmann
  

Links

• International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests)