Management driven changes (1967–2005) in soil acidity and the understorey plant community following conversion of a coppice-with-standards forest

Forest management regimes influence plant diversity and soil properties. Many European forests were traditionally managed as coppice-with-standards of which the majority are nowadays being converted to or have been converted to high forest systems. To evaluate the impact of these changes on abiotic and biotic characteristics, long-term data are needed. Here results are presented from the 245 ha Tournibus forest (Belgium) where soil acidity was determined and vegetation records were made in 1967 and 2005 for 246 semi-permanent plots. In 1967 most of the forest was managed as coppice-with-standards, whereas in 2005 stands were managed as high forest (either uneven-aged high forest, even-aged high forest with Quercus spp., or even-aged high forest with Fagus spp.).We determined if soil acidity (at 5 and 45 cm depth) and understorey vegetation related characteristics changed between 1967 and 2005 for the whole forest and if conversion types differentially influenced these variables. Each conversion type was also characterised in terms of canopy and forest floor/topsoil derived factors.Soil acidity at 5 cm depth increased and the magnitude depended on conversion type and initial soil acidity. No soil acidification was observed at 45 cm. Significant overall increases were found for: α-diversity (i.e. plot species richness), the proportion of ruderal species and Ellenberg indicator values for soil moisture, soil reaction and soil nitrogen. On the contrary, β-diversity (i.e. the degree of change in species identities among plots) and the proportion of competitive and stress-tolerant species on average decreased significantly. Moreover, conversion type differentially affected the magnitude of change for all variables, except α-diversity. Conversion to even-aged high forest led to larger departures from the 1967 situation than conversion to uneven-aged high forest. Most changes were interpreted as abiotic or biotic homogenization, which are likely not independent: increased convergence of abiotic factors within a conversion type (mainly even-aged high forest) most likely has led to biotic homogenization.