Tree-to-tree competition in mixed European beech-Scots pine forests has different impacts on growth and water-use efficiency depending on site conditions

1. Mixed conifer-hardwood forests can be more productive than pure forests and they are increasingly considered as ecosystems that could provide adaptation strategies in the face of global change. However, the combined effects of tree-to-tree competition, rising atmospheric CO2 concentrations and climate on such mixtures remain poorly characterized and understood. 2. To fill this research gap, we reconstructed 34-year series (1980-2013) of growth (basal area increment, BAI) and intrinsic water-use efficiency (iWUE) of Scots pine (Pinus sylvestris L.) – European beech (Fagus sylvatica L.) mixed stands at two climatically contrasting sites located in the southwestern Pyrenees. We also gathered data on tree-to-tree competition and climate variables in order to test the hypotheses that (i) radial growth will be greater when inter-specific competition exceeds intra-specific competition, i.e. when species complementarity occurs, and (ii) enhanced iWUE could be linked to improved stem radial g...

1. 针阔混交林的生产力高于纯林，且日益被视为可应对全球变化、提供适应性策略的生态系统。然而，树木间竞争、大气CO₂浓度升高与气候对这类混交林的综合影响仍缺乏系统性刻画与深入认知。
2. 为填补这一研究空白，本研究重建了位于比利牛斯山脉西南部两个气候差异显著站点的欧洲赤松（*Pinus sylvestris L.*）-欧洲山毛榉（*Fagus sylvatica L.*）混交林长达34年（1980-2013年）的生长指标（断面积生长量，basal area increment, BAI）与内在水分利用效率（intrinsic water-use efficiency, iWUE）序列。同时我们还收集了树木间竞争与气候变量数据，以验证以下假说：(i) 当种间竞争强于种内竞争（即发生物种互补效应）时，径向生长量更高；(ii) 内在水分利用效率的提升可能与茎干径向生长的改善相关……