Explaining the large-scale diversity of soil organisms that drive biogeochemical processes-and their responses to environmental change-is critical. However, identifying consistent drivers of belowground diversity and abundance for some soil organisms at large spatial scales remains problematic. Here we investigate a major guild, the ectomycorrhizal fungi, across European forests at a spatial scale and resolution that is-to our knowledge-unprecedented, to explore key biotic and abiotic predictors of ectomycorrhizal diversity and to identify dominant responses and thresholds for change across complex environmental gradients. We show the effect of 38 host, environment, climate and geographical variables on ectomycorrhizal diversity, and define thresholds of community change for key variables. We quantify host specificity and reveal plasticity in functional traits involved in soil foraging across gradients. We conclude that environmental and host factors explain most of the variation in ectomycorrhizal diversity, that the environmental thresholds used as major ecosystem assessment tools need adjustment and that the importance of belowground specificity and plasticity has previously been underappreciated.

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Crown transparency estimates of Scots pine, Norway spruce, common beech, pedunculate and sessile oak, annually surveyed between 1990 and 2004 within a grid over Germany, provide a suitable response variable to study drought effects on forest trees. Major climatic factors, available on a monthly basis as plot-specifically interpolated values and parameters of site and stand conditions, biotic and other relevant factors were used as predictors in different cross-and length-sectional, and longitudinal models. Stand age is a considerable and most constant driver of crown transparency in all species. Pine, spruce and beech responded-mainly with a delay of 1 year-with some foliar loss in areas where there was a surplus of temperature after the generally hot and dry summer of 2003. Parallel time-series analyses delivered species-specific geographic large-scale patterns with delayed or recent precipitation deficits or temperature surpluses. Even if beech is partly responding in current years with leaf loss towards precipitation surpluses, defoliation is especially high 1 year after hot summers, partly a result of high seed sets after such summers. Crown condition of oak responds in dry and warm areas according to the drought stress hypothesis, however, in cool and wet mountainous ranges oak responds after wet summers with higher defoliation.Longitudinal approaches revealed for all 4-tree species significant relationships between crown condition and deviations from the long-term means of temperature, precipitation but also global radiation and wind speed. Results do not always match the drought stress hypothesis, however, this is not to expect considering the heterogeneous site, stand and climatic conditions across Germany. Complex interactions of climatic and biotic factors also impede simple relationships. Soil-related clusters reveal higher sensitivity of spruce and beech towards climatic drought factors on more acid soils with thin humus layers. Also clusters constructed from plotspecific courses of defoliation reveal groups with rather closer relationships like a group of pine plots in the Oberpfalz, which seems to be especially sensitive to summer drought.

As a part of the 'Intensive Forest Monitoring Programme' of ICP Forests, ground floor vegetation has been surveyed along with parameters of other relevant components of the forest ecosystems and their environment at 80 permanent plots all over Germany. Its floristic composition and their changes can therefore be linked to a wide variety of potentially influencing factors, scrutinising recent hypotheses on floristic changes, mainly soil eutrophication and acidification due to air pollutants. Results of a broad-scaled feasibility study are presented and critically discussed with regard to future in-depth evaluations. After an overview on the most abundant species, the syntaxonomic allocation of the plots is given. An ordination reveals a gradient from nutrient and base rich soils to poor acidic soils. Floristic dynamics are mainly aligned with the main axis, but conclusions about the medium-term development cannot be stated yet. Ordination and subsequent statistics are recommended to open up a wide field for explorative investigations. Indicator values for soil acidity and nutrient supply corroborate the main floristic gradient. Based on an empirical species-area relationship (SAR), species numbers for a common plot size of 400 m 2 were calculated. Basic relationships among different diversity measures and between diversity measures and basic stand and site-related parameters were elaborated. Recommendations focus on enhancements of the assessment of ground floor vegetation within the context of the Level II monitoring like annual sampling or harmonisation of the plot sizes.

The assessment of crown condition is an annually repeated core activity within the 'Intensive Forest Monitoring Programme' (Level II monitoring) at selected plots. As the intensive monitoring focuses on a better understanding of direct and indirect effects of air pollution at the ecosystem level, a considerable number of parameters are collected. This allows the analysis of numerous relationships which may determine tree-crown condition with respect to different ecological situations and their temporal variation. This article describes possibilities for integrated evaluations of crown condition data within the German Level II programme. Besides descriptions of defoliation and mortality rates over time, relationships among defoliation, and stand and site characteristics and sampling circumstances are explored. Autocorrelative properties of defoliation data are also described. The results reveal that the date of the field assessment is influential in three out of four species, while the dominance structure has effects in Scots pine and oak. Temporal variation of defoliation reveals strong plot-specific characteristics with limited possibilities for generalisations. Species-specific temporal autocorrelation structures were detected. Within integrated approaches, the 'federal state' variable gains high coefficients of determination; however, alternative models incorporating significant ecological factors also reveal plausible explanations. Interactions between predictors complicate the statistical approaches. This is also true for models that include temporal aspects of defoliation and indicators of climatic drought stress. Methodological limitations and significant interpretations are discussed. Statistical evaluations are restricted mainly by the low number of cases, limiting the number of predictors within multiple models. In the future, both a consequent processing of the collected data according to relevant questions and the application of advanced statistical models will be needed.