Structure and growth of mixed Scots pine/European beech stands compared with pure stands analyzed along an ecological gradient through Europe

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Emerging properties in species mixtures and causes of overyielding are hardly clarified, but important for the understanding and the prediction of mixed stand dynamics and for the designing of resource efficient production systems. This project would be focused on mixtures of Scots pine and European beech. Their complementary ecological traits might cause overyielding at present and may become even more stabilizing and thereby relevant in future under a changed climate. We would base the project on a unique dataset of 30 triplets of mature and fully stocked mixed and pure stands of Scots pine and European beech located along an ecological gradient through Europe, which are already established, measured, and sampled by increment coring. The applicant organized the establishment of those triplets acting as vice chair of COST action EuMIXFOR 1206 for the purpose of standardization and harmonization of mixed stand research. For this proposed project the already available tree data, increment cores, and stand data will be complemented by measurements of light and water conditions so that the following questions can be answered.-How does species mixing affect productivity and maximum stand density -carrying capacity- at the stand level. Any overyielding and increase of maximum stand density would indicate a positive net effect of simultaneously occurring competition and facilitation. -In order to better understand the modification of the mixing effects by supply, capture and use efficiency of resources, we secondly scrutinize how the mixing effect changes along an ecological gradient from nutrient poor and dry sites to fertile and moist sites. -Based on the retrospective tree ring data we will analyse the temporal variability and dependency of mixing effects from the prevailing annual weather conditions. -By analysing individual tree structure, growth, and size distributions we can trace mixing effects from the tree to the stand level and reveal which subset of trees, i.e., which hierarchical stratum contributes to over- or underyielding of mixed versus pure stands. -Based on additional light and soil moisture measurements we will question how the mixing effects are modulated by the interplay between light and water supply, capture, and use efficiency.Mixtures of Scots pine and European beech get more attention in view of climate change and the ongoing transition from pure conifer stands to mixtures of conifers with broadleaved trees. Revelation of the spatial and temporal inter-specific interactions, there dependency of resource conditions and there outcomes in terms of productivity may contribute to better understanding, modelling and designing of resource efficient production systems.