PROBLEMS IN VEGETATION MONITORING IN NATURE MANAGEMENT PRACTICE: TWO CASE STUDIES

One of the major requirements of the monitoring of vegetation is the comparability of data between years. Therefore, a proper sampling scheme is essential. However, through the years, in nature management practice lots of data collected without a primary monitoring goal. Afterwards, it often seems very valuable to include these older data in the analysis for several reasons. In two examples from military ranges in the Netherlands, two of the problems which can be met with in comparing unequivalent or biased data in monitoring are shown. In the first example, the frequency of grassland species in two sets of relevés is examined. A solution is presented for the overrepresentation of relevés from one or more vegetation types from the first year, based on the area of the vegetation types on the vegetation map of this same year. In the second example, two sequential vegetation maps are compared. A major problem is often the thematic incongruence of sequential vegetation maps. Afterwards, this can only be resolved by upscaling one or both maps. It is concluded that the use of old data for monitoring purposes can be very valuable, but that this often calls for creative data handling, in which GIS and modern computer programmes are very helpful.