Strict forest nature reserves research in Bavaria - analysis of vegetation data for ecological long-term observation

A recent research concept prioritises 26 out of Bavaria's 159 strict forest nature reserves for long-term observation. In 2013 the first permanent plot sample for ecological studies was established in four of the priority reserves. A total of 24 circular 314 m(2) vegetation plots were located within the large (1 ha) permanent core areas of six priority reserves. The concept for long-term observation of natural forests is presented, pathways of analysis are outlined and exemplified on the basis of the 2013 vegetation data. Because plots are inevitably spatially autocorrelated, they were coupled with a representative reference from the whole of Bavaria. The latter data set comprises 313 plots in strict forest nature reserves which were selected to represent the potential natural vegetation of plots in the 8 x 8 km grid of the "Forest Soil Condition Survey" (BZE II; EWALD 2009). Detrended Correspondence Analysis (DCA) was used to detect gradients of species composition and corresponding plot groupings. Thus, the newly collected plots were classified independently and impartially on the base of their floristic similarity to reference vegetation types. The subsequent characterisation of vegetation types was performed by ordering phytosociological tables. The newly collected data comprise beech forests on limestone (Hordelymo-Fagetum) and on siliceous substrates (Galio- and Luzulo-Fagetum), as well as mixed forests of unstable hillsides (Adoxo-Aceretum) and riverine forests (Pruno-Fraxinetum, Querco-Ulmetum). Post-hoc correlation with Ellenberg indicator values suggested soil reaction and nutrient availability as putative drivers of species turnover along the first axis; species turnover along the second axis was apparently caused by a temperature gradient. While these correlations are congruent between ordinations of the newly collected and the reference data set, the temperature gradient (featuring low Ellenberg temperature values) in the new plots appears as a pseudo-effect due to cultivated conifers. Opportunities for data analysis will gradually increase within the next two decades, and, with the data set of the 26 priority reserves completed, the long-term observation of vegetation dynamics in beech forests as well as at the temperature- and moisture-induced margins of beech distribution will become pivotal.