Ecosystem dynamics in dry heathlands: spatial and temporal effects of environmental drivers on the vegetation

To understand and estimate the effects of environmental drivers on temperate dry heathland vegetation, pin-point cover data from 102 Danish sites sampled during a 16-year period was regressed onto selected environmental variables. The effects of nitrogen deposition, soil pH, soil C-N ratio, soil type, precipitation and grazing on the heathland vegetation was modelled in a spatio-temporal structural equation model using a Bayesian hierarchical model structure. The results suggest that the modelled environmental variables have important regulating effects on the large-scale spatial variation as well as plant community dynamics in dry heathlands. The cover of the dwarf shrub Calluna vulgaris, which is the characteristic species of dry heathlands, increased in relatively sandy soils with a relatively high C/N ratio. The cover of the grass Avenella flexuosa increased markedly at relatively high nitrogen deposition and low precipitation. The cover of other graminoids, of which Molinia caerulea is the most abundant, increases with a relatively low C/N ratio, low grazing pressure, and clayey soils. It was concluded that the modeled environmental variables are sufficient for predicting the average plant community dynamics of dry heathlands. Consequently, the model may be used to make forecasts for the effect of different management scenarios at a specific site and thus provide important input to setting up local adaptive management plans.