Forest stand productivity derived from site conditions: an assessment of old Douglas-fir stands (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) in Central Europe

Douglas-fir growth correlates with the climate, the soil moisture regime, and the soil nutrient status, reflecting a broad physiological amplitude. Even though planting this non-native tree species is suggested as a viable strategy to improve adaptiveness of European forests to a more extreme climate and to assure future productivity, the expected temperature increase may induce a decline in forest stand productivity for Douglas-fir in already warm and dry regions.

Context Tree species selection is one of the most important forest management decisions to enhance forest productivity and stand stability on a given site. Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii), a non-native species from north-western America, is seen as an important additional species option for adapting Central European forests to a changing climate.
Aims This study assesses Douglas-fir forest productivity derived from site conditions. We investigate climatic and physico-chemical soil characteristics and productivity of 28 mature Douglas-fir stands growing on siliceous, as well as carbonate bedrock material in southern Germany and north-eastern Austria.
Methods The importance of climatic and physico-chemical soil characteristics was analyzed with the machine learning method Random Forests.
Results The results show that Douglas-fir growth correlates with climate, soil moisture, and soil nutrient availability derived from ten climatic and physico-chemical soil parameters.
Conclusion The broad pH optimum between 4.5 and 7.2 reflects the broad physiological amplitude of Douglas-fir, and no significant differences were detectable between carbonate and siliceous bedrock. We also conclude that climate change may induce a forest stand productivity decline, because lower productivity with the highest mean summer temperature across our study range was observed at the warmest sites in Eastern Austria.

Keywords
Non-native tree species, Climate change adaptation, Site conditions, Site index

Open access publication
Eckhart, T., Pötzelsberger, E., Koeck, R. et al. Annals of Forest Science (2019) 76: 19. https://doi.org/10.1007/s13595-019-0805-3

Data availability
The dataset generated during and/or analyzed during the current study is available in the Figshare repository Eckhart et al. (2019) DF_site_growth_data. V1. FigShare. [Dataset]. https://doi.org/10.6084/m9.figshare.7553384.v1