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Sanderson, M. A., Skinner, R. H., Barker, D. J., Edwards, G. R., Tracy, B. F., Wedin, D. A. (2004): Plant species diversity and management of temperate forage and grazing land ecosystems.
Authors:I. Geedicke, M. Schultz, B. Rudolph, and J. Oldeland
Species richness is a widespread measure to evaluate the effect of different management histories on plant communities and their biodiversity. However, analysing the phylogenetic structure of plant communities could provide new insights into the effects of different management methods on community assemblages and provide further guidance for conservation decisions. Heathlands require permanent management to ensure the existence of such a cultural landscape. While traditional management with grazing is time consuming, mechanical methods are often applied but their consequences on the phylogenetic community assemblages are still unclear. We sampled 60 vegetation plots in dry sandy heathlands (EU habitat type 2310) in northern Germany stratified by five different heathland management histories: fire, plaggen (turf cutting), mowing, deforestation and intensive grazing. Due to the distant relationship of vascular plants and lichens, we assembled two phylogenetic trees, one for vascular plants and one for lichens. We then calculated phylogenetic diversity (PD) and measures of phylogenetic community structure for vascular plant and lichen communities. Deforested areas supported significantly higher PD values for vascular plant communities. We found that PD was strongly correlated with species richness (SR) but the calculation of rarefied PD was uncorrelated to SR leading to a different ranking of management histories. We observed phylogenetic clustering in the lichen communities but not for vascular plants. Thus, management by mowing and intensive grazing promotes habitat filtering of lichens, while management histories that cause greater disturbance such as fire and plaggen do not seem to affect phylogenetic community structure. The set of management strategies fulfilled the goals of the managers in maintaining a healthy heathland community structure. However, management strategies that cause less disturbance can offer an additional range of habitat for other taxonomic groups such as lichen communities.
We used space-for-time substitution to obtain a directed successional sequence for subalpine meadow vegetation in the Swiss National Park. Since human impacts (e.g., domestic animal grazing) ceased in 1914, the successional processes documented are assumed to be autogenic in nature. The data consist of 59 permanent plots spanning almost 90 years, and include many spatial replications. An initial inspection of the individual time series revealed the existence of a variety of response patterns, which are described in the literature as representing different successional types. However, a closer inspection suggested that many of these series can be superimposed, as they are part of a much longer deterministic series. Linking the individual time series proved to be challenging. A heuristic approach produced results that differed depending on initial starting conditions. We therefore derived a deterministic algorithm to produce a unique solution. The resulting sequence largely confirmed the heuristic interpretation, suggesting a trend from early successional (post-grazing) grassland to pine invasion spanning about 400 years. This timespan is valid only for the climatic conditions near the treeline, and for plant species specific to the study site. Our results suggest that the various species temporal response models described in the literature may be artifactual, representing portions of underlying Gaussian responses. The data also indicate that species assemblages may persist for several decades with only minor fluctuations, only to change suddenly for no apparent reason.