As groundwater flow is unidirectional and continual in springs, plants and their diversity in spring habitats is expected to be controlled mainly by hydrochemical conditions. To test which environmental compartments the vegetation of springs is reflecting in fact, we investigated the influence of springwater hydrochemical properties, catchment traits, and spatial configuration on plant species composition of springs in forested catchments.

Many of those, especially on siliceous bedrock, have been strongly influenced by atmospheric depositions, which is reflected by the acidification of ground and surface waters. The temporal dynamics of springwater quality and associated vegetation were investigated by means of repeated measurements in 102 springs from 1989 to 2006.

Vascular plants, mosses and liverworts have been tested in a former project to identify (1) the driving forces of species composition and (2) indicator species, which react sensibly to changes in water chemistry.

In a recent project we repeated the investigation of springwater chemistry and vegetation on different spatial and temporal scales, (3) to test if there is a recovery from acidification (as a consequence of the reduced deposition of acidifying pollutants) and (4) to quantify amplitude and delay of plant species’ and community response.

Hydrochemical conditions are found to be more important than physical or spatial factors. Low pH-values accompanied by high concentrations of Al, Cd, Zn and Mn are the main factor that is related to species composition. By means of multivariate ordination techniques Chrysosplenium oppositifolium and Cardamine amara are identified as indicator species for non-acidic water chemistry, whereas the mosses Spagnum fallax and Polytrichum commune are found to be dominant under acidic conditions.

Surprisingly, changes in dominance of these selected indicator species can not be directly linked to trends in acidification. While we found a slight trend of recovery from acidification in springwater from 1989 to 2006, the predefined indicator species did not reflect that change. This could be caused by either a delayed reaction due to persistent dominance patterns (inertia) or a longer-integrating reaction, compensating short-term fluctuations in water chemistry. In contrast the response of the whole plant community shows first signs of recovery, which suggests the existence of faster responding species.

Seepage zone vegetation proves to be a good indicator system to characterise groundwater chemistry, which in turn reflects the geochemical and hydrological conditions of forested catchments. Spatial patterns of spring vegetation emerge at various spatial scales and can provide valuable ecological information. Hence we propose to continue this long-term research, .especially because it is to expect that also climate change will affect those habitats, which are originally featured by their relative constancy of hydrophysical and hydrochemical parameters.