Monitoring Temporal Change

As spatially and temporally explicit, detailed representations of vegetation, phytosociological releves and maps are appropriate tools for monitoring change in plant species composition and the underlying environmental conditions. Thus, fine-scale monitoring systems in agriculture, forestry, nature conservation, and civil engineering have used repeated phytosociological releves at permanently marked locations over many decades, which allow us to analyze trends in diversity of species and species groups (such as Ellenberg indicators or plant functional types). Besides detecting gradual changes, phytosociology expresses succession as a change of community types. Where many permanent plots conform to the same rules, succession can be generalized into temporal gradients and/ or sequences of community types (seres). However, many phytosociological succession models have been based on comparative observation (space-for-time substitution) rather than real time series. Larger groups of old releves without permanent marking are sometimes used to detect succesional trends by making new releves in the supposed old positions ('quasi-permanent plots') and by detecting systematic differences between old and new data.

Repeated mapping may reveal changes in the spatial delimitation of vegetation units and allow representation of succession in a transition matrix. However, its validity crucially depends on fully operational mapping keys that unequivocally define the criteria for drawing boundaries between types.

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