Das Projekt verfolgte folgende Ziele:
Funded by the Bavarian State Forest Authority, the MARGINS project will forecast reactions of temperate tree species to increasing temperature and drought based on a combination of species distribution modeling and study of populations at the warm and dry edges of the distributions. Background Ecological niche models identify thresholds for physiological existence (i.e., fundamental niche) or observability of species (i.e., realized niche). The model output are probabilities of occurence, whereas the highest probabilities are found in the niche center, with probabilities converging to zero towards the margins. Validation with real observations reveals that beyond certain thresholds no occurrences of the species in question can be ascertained.
The specification of these threshold values for the commercially important tree species of Bavaria is the central scope of the MARGINS project. Aims Niche models applied to geographic areas result in species distribution models (SDM), where the probabilities of occurrence are mapped onto geographic zones. Occurrences just before the distributional margins represent populations under extreme climatic influence. Hence, symptoms induced by climatic change should become visible in these populations "at the rear edges" first. Studying these extreme populations is the core part of the MARGINS project, and SDM are used to identify interesting populations, and later to transfer the obtained results to future conditions in Bavaria.
Aiming at the combination of the strengths of both statistical niche modeling and effect-oriented case studies in a space-for-time approach, the MARGINS project aims to:
The HSWT workpackage within MARGINS studies vegetation composition and plant traits of tree populations. We collect plot data in ain the field and assemble a reference database using existing data from partners throughout Southern Europe.
In 2013 and 2014 45 MARGINS-plots have been sampled at the southern distribution edge of beech, spruce, fir, Scots pine and sessile oak. We found a total of 432 vascular plant species, among them 59 tree species. Species composition was highly similar to the one found in Bavarian forests. Site index (dominant height at 100 yrs.) indicated average growth conditions. Radial growth in Spain was limited by high summer temperatures and low precipitation of the previous year, with a diminishing influence of the north-atlantic oscillation. In 12 beech stands throughout the Mediterranean it was demonstrated, that radial growth chiefly depended on summer temperatures, with a diminishing influence of precipitation in the western, yet still significant effects in the central and eastern regions. In many plots a diminishing growth trend was detectable.
The concept of “site marginality” was elaborated in a paper submitted to the journal Forestry. Models of the niche edge are designed to define climatic limits of forest tree species more sharply, but they are limited by a lack of high resolution soil information. Based on the newly built occurrence database, the outer tolerance limit was defined as the most extreme climate (in terms of warmth and aridity), at which the specis occurs under favourable conditions of soil and relief. Based on the systematic sample of ICP Forests Level-I plots, the so-called “impact” was estimated from an ensemble of 63 climate change scenarios. Marginality proved to be a robust estimate of the sensitivity of a given situation (tree species, current climate) towards climate change. As a summary parameter, impact explicitly encompasses the diversity of scenarios and model uncertainty. Such a representation of climate risk improves decision support in tree species selection under climate change.
Mellert, K. H., Ewald, J., Hornstein, D. et al. (2015): Climatic marginality: a new metric for the susceptibility of tree species to warming exemplified by Fagus sylvatica (L.) and Ellenberg’s quotient. European Journal of Forest Research. Eur. J. Forest Res. 135: 137-152