Tumajer Jan, Altman Jan, Lehejček Jiří
Department of Physical Geography and Geoecology, Faculty of Science, Charles University, Albertov 6, 12843 Prague, Czech Republic.
Institute of Botany, The Czech Academy of Sciences, Dukelská 135, 37901 Třeboň, Czech Republic; Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Kamýcká 129, 165 21 Prague 6, Suchdol, Czech Republic.
Sci Total Environ. 2023 Dec 20;905:167153. doi: 10.1016/j.scitotenv.2023.167153. Epub 2023 Sep 18.
Boreal forests represent an important carbon sink and, therefore, significantly contribute to climate change mitigation. Tree-ring width series of boreal species reflect climate variation at the moment of tree-ring formation but also lagged climatic effects from dormancy preceding tree-ring formation and antecedent growing seasons. However, little is known about how the growth sensitivity to climate in specific intra-annual periods varies across the landscape. Here, we assessed growth responses to climate variation during the 45 months preceding the tree-ring formation for nine boreal stands of Picea glauca and Picea mariana distributed along the gradients of elevation and slope aspect. We combined process-based modeling of wood formation and remote sensing data to determine growth phenology at each site. Next, we classified intra-annual seasons with significant climate-growth correlations based on the timing of dormancy and growth periods. Both the phenology and the climate-growth relationships systematically shifted with elevation and, to a lower extent, also with slope orientation at the treeline. The mean duration of the growing season varied between 100 days at treelines above 900 m and 160 days at lowlands below 500 m. The growth at treelines was stimulated by temperature in the summer of the tree-ring formation year and two years before tree-ring formation. The period of significant climate-growth correlations during the current summer did not exceed three months in agreement with the local duration of the growing season. The growth of trees in lower elevations was instead stimulated by high temperature during the dormancy periods but restricted by high temperature in antecedent summer seasons. In conclusion, our study highlights the linkage between the timing of climate-growth sensitivity and growth phenology, primarily determined by proximity to the treeline. Consequently, accounting for landscape gradients in growth phenology is crucial for upscaling the climatic limits of boreal stands' growth as climate change progresses.
北方森林是重要的碳汇，因此对缓解气候变化有显著贡献。北方树种的年轮宽度序列反映了年轮形成时的气候变化，但也受年轮形成前休眠期和前几个生长季滞后气候效应的影响。然而，对于特定年内时期内树木生长对气候的敏感性如何在整个景观中变化，人们知之甚少。在这里，我们评估了沿海拔和坡面梯度分布的9个白云杉和黑云杉北方林分在年轮形成前45个月内对气候变化的生长响应。我们将基于过程的木材形成模型与遥感数据相结合，以确定每个地点的生长物候。接下来，我们根据休眠期和生长期的时间对具有显著气候 - 生长相关性的年内季节进行分类。物候以及气候 - 生长关系都随着海拔高度而系统性地变化，并且在较小程度上也随着树线处的坡面方向而变化。生长季的平均持续时间在海拔900米以上的树线处为100天，在海拔500米以下的低地为160天。树线处的生长受到年轮形成当年夏季以及年轮形成前两年夏季温度的刺激。当前夏季显著气候 - 生长相关性的时期不超过三个月，这与当地生长季的持续时间一致。相反，低海拔地区树木的生长受到休眠期高温的刺激，但受到前一个夏季高温的限制。总之，我们的研究强调了气候 - 生长敏感性的时间与生长物候之间的联系，这主要由与树线的距离决定。因此，随着气候变化的推进，考虑生长物候的景观梯度对于扩大北方林分生长的气候极限至关重要。
