Projecting tree-growth responses into future climate: A study case from a Danish-wide common garden

- Eight forest tree species show differing growth responses to drought.
- Broadleaved species were less responsive to drought than conifers.
- Species responded diversely to previous autumn and/or current spring temperatures.
- Growth predictions for 2071-2100 will vary between −16% and +12%.

Assessing growth responses to climate variations from common garden experiments is vital to identify a species portfolio matching future climate. In the present study we make use of a 50 years old common garden experiment spanning six sites with different soil types across Denmark to (i) analyse climate-growth responses and resilience to drought and (ii) model future growth predictions for six non-native conifers and two native broadleaved tree species. Species-specific response-functions and Superposed Epoch Analysis of drought events are used to assess differences in sensitivity to drought.The results show that the growth of all species, except for Quercus robur L., are significantly (P < 0.05) and negatively correlated with summer drought from June-August in at least one of the sites, whereby Larix kaempferi (Lamb.) Carr, Abies grandis (Dougl.) Lindl., Picea sitchensis (Bong.) Carr., and Picea abies (L.) Karst. are the less resilient. Negative effects of previous warm autumn or late summer were found for P. abies, A. grandis, Abies alba Mill. and Pseudotsuga menziesii (Mirb.) Franco. Moreover, independently of the site conditions, our model projections of growth responses under future climate prediction (RCP4.5 emission scenario) forecast that growth of L. kaempferi, A. grandis, P. abies and Fagus sylvatica L. will be reduced by up to 10-16% by 2100. Minor changes in growth responses are expected for P. sitchensis, A. alba and P. menziesii, while Q. robur will increase by 12%.This study demonstrates how such projections based on old common garden experiments could be used as inputs to today's forest management decisions.