Department of Silviculture and Forest Ecology of the Temperate Zones, Faculty of Forest Sciences and Forest Ecology, University of Göttingen, Büsgenweg 1, 37077 Göttingen, Germany.
Department of Forest Growth, Northwest German Forest Research Institute (NW-FVA), Grätzelstraße 2, 37079 Göttingen, Germany.
Tree Physiol. 2024 Oct 3;44(10). doi: 10.1093/treephys/tpae114.
Mixed-species forests are, for multiple reasons, promising options for forest management in Central Europe. However, the extent to which interspecific competition affects tree hydrological processes is not clear. High-resolution dendrometers capture subdaily variations in stem diameter; they can simultaneously monitor stem growth (irreversible changes in diameter) and water status (reversible changes) of individual trees. Using the information on water status, we aimed to assess potential effects of tree species mixture, expressed as local neighborhood identity, on night-time rehydration and water stress. We deployed 112 sensors in pure and mixed forest stands of European beech, Norway spruce and Douglas fir on four sites in the northwestern Germany, measuring stem diameter in 10-min intervals for a period of four years (2019-2022). In a mixture distribution model, we used environmental variables, namely soil matric potential, atmospheric vapor pressure deficit, temperature, precipitation and neighborhood identity to explain night-time rehydration, measured as the daily minimum tree water deficit (TWDmin). TWDmin was used as a daily indicator of water stress and the daily occurrence of sufficient water supply, allowing for stem growth (potential growth). We found that species and neighborhood identity affected night-time rehydration, but the impacts varied depending on soil water availability. While there was no effect at high water availability, increasing drought revealed species-specific patterns. Beech improved night-time rehydration in mixture with Douglas fir, but not in mixture with spruce. Douglas fir, however, only improved rehydration at a smaller share of beech in the neighborhood, while beech dominance tended to reverse this effect. Spruce was adversely affected when mixed with beech. At species level and under dry conditions, we found that night-time rehydration was reduced in all species, but beech had a greater capacity to rehydrate under high to moderate soil water availability than the conifers, even under high atmospheric water demand. Our study gives new insights into neighborhood effects on tree water status and highlights the importance of species-specific characteristics for tree-water relations in mixed-species forests. It shows that drought stress of European beech can be reduced by admixing Douglas fir, which may point towards a strategy to adapt beech stands to climate change.
混交林由于多种原因是中欧森林管理的有前途的选择。然而，种间竞争对树木水文过程的影响程度尚不清楚。高分辨率的树木测径器可以捕捉树干直径的亚日变化；它们可以同时监测单个树木的树干生长（直径的不可逆变化）和水分状况（可逆变化）。利用水分状况的信息，我们旨在评估树种混合（表现为局部近邻身份）对夜间补水和水分胁迫的潜在影响。我们在德国西北部的四个地点的欧洲山毛榉、挪威云杉和花旗松的纯林和混交林中部署了 112 个传感器，在四年（2019-2022 年）的时间内以 10 分钟的间隔测量树干直径。在一个混合分布模型中，我们使用环境变量，即土壤基质势、大气蒸气压亏缺、温度、降水和近邻身份来解释夜间补水，以每日最小树木水分亏缺（TWDmin）来衡量。TWDmin 被用作水分胁迫的每日指标和充分供水的每日发生情况，从而允许树干生长（潜在生长）。我们发现，树种和近邻身份影响夜间补水，但影响因土壤水分可用性而异。在高水分可用性的情况下没有影响，但干旱加剧则显示出物种特异性模式。山毛榉在与花旗松的混合中改善了夜间补水，但在与云杉的混合中则没有。然而，当近邻中花旗松的比例较小时，花旗松才会改善补水，而山毛榉的主导地位则倾向于扭转这种效果。云杉与山毛榉混合时则受到不利影响。在物种水平和干旱条件下，我们发现所有树种的夜间补水都减少了，但在高至中等土壤水分可用性下，山毛榉的补水能力比针叶树更强，即使在大气水分需求较高的情况下也是如此。我们的研究提供了有关树木水分状况的近邻效应的新见解，并强调了树种特异性特征对混交林树木-水分关系的重要性。它表明，通过混入花旗松可以减少欧洲山毛榉的干旱胁迫，这可能为适应山毛榉林适应气候变化提供了一种策略。
