Correspondence of the fine-scale spatial variation in soil chemistry and the herb layer vegetation in beech forests

The objective of this paper is to analyse the degree to which the variation in soil conditions corresponds to the occurrence of specific plant species at micro-scale. The investigation was performed in beech forests with seven plant species growing on three sites with different geological substrates of the Triassic period (Muschelkalk, Oberer and Mittlerer Buntsandstein). At each site three to five plant species of ca. 20 individuals each were selected by stratified random sampling. The growth location of a plant individual was considered to be a potential microsite. At the gowth locations, soil solution was exctracted in situ by low tension lysimetry from the rooted topsoil exactly beneath the selected plant individuals. A soil sample was taken from the same spot and analysed for pH(H₂O) and exchangeable cations. In addition, the vegetation was recorded around each target individual and species composition was related to chemical soil properties by multivariate analyses.

The three sites were found to form a gradient with respect to most analysed soil parameters. Variation coefficients of soil properties increased in the sequence pH, exchangeable Ca, K, Mg, Al, Fe, Mn. Concentrations of cations in the soil solution varied to a higher degree than those of exchangeable cations with the sole exception of Fe that showed a lower variation in the soil solution. Averaged over all sites, the microsite values for pH and exchangeable Ca exhibited a distinct sequence for the investigated species with decreasing values in the root horizon in the sequence Mercurialis perennis, Arum maculatum, Lamiastrum galeobdolon, Galium odoratum, Viola reichenbachiana, Oxalis acetosella and Luzula luzuloides. Within sites, only few significant differences were found between the potential microsites of specific species. The microsites of species on Muschelkalk differed in pH, concentrations of exchangeable Ca and K and of Ca in the soil solution. The microsites on Mittlerer Buntsandstein differed in pH and concentration of exchangeable Fe. No significant differences between species were found on Oberer Buntsandstein. Species composition in a area of 3.14 m² around the sample locations varied only to a minor degree as was revealed by canonical correspondence analysis (CCA). In addition, the low level of encountered variation could only be explained to a small degree by the soil variables.

It is concluded that the analysed environmental factors are of minor importance for fine-scale species occurrences. At a scale of meters or less, biotic parameters might exert a greater influence than soil parameters.