Crown condition within integrated evaluations of Level II monitoring data at the German level

Abstract

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.

Outline and examples for integrated evaluations of data from the intensive (Level II) monitoring of forest ecosystems in Germany

“…Handling temporal and spatial autocorrelative effects within different biological phenomena including defoliation is another important issue of further in-depth evaluations (cf Musio et al 2004). Figure 2 exemplifies a basic integrative step at hand of defoliation values of individual trees (cf Seidling 2004). While mean defoliation is almost constant over time, a group of six trees shows a deviant behaviour since 1992.…”

“…Parameter specific considerations may include the generation of new, more or less aggregated, or derived parameters like mortality rates calculated on the basis of trees with 100% defoliation (Seidling 2004). Other examples are molar ratios between foliar or soil element concentrations (Sverdrup and Warfvinge 1993) or indicator values derived from the floristic composition of the Fig.…”

“…Lorenz et al 2003;BMVEL 2004). As Seidling (2004) deals with evaluations of defoliation at Level II plots in greater detail, one aspect especially important for integrated studies is emphasised: can it be secured such that we deal with spatially and temporally consistent data sets? This question was already brought up, e.g.…”

“…Crown visibility and crown shadowing are further parameters documented on the basis of individual trees from 1997 onwards. This information was included in an overall approach (Seidling 2004); however, investigations on a plot-wise basis or with nested models are outstanding.…”

Wood production, wood technology, and biotechnological impacts

“…Considering additional parameters from evaluation of Level II plots allows integrated analysis of complex relationships in different ecological situations and their temporal variation. Stress effects on the complex forest systems by direct or indirect impact of air pollutants and soil acidification are expected to become more transparent (Seidling 2004, Seidling & Mues 2005.…”