School for Environment and Sustainability, University of Michigan, Ann Arbor, MI, USA.
Glob Chang Biol. 2021 Aug;27(16):3883-3897. doi: 10.1111/gcb.15678. Epub 2021 Jun 5.
Phenological escape, a strategy that deciduous understory plants use to access direct light in spring by leafing out before the canopy closes, plays an important role in shaping the recruitment of temperate tree seedlings. Previous studies have investigated how climate change will alter these dynamics for herbaceous species, but there is a knowledge gap related to how woody species such as tree seedlings will be affected. Here, we modeled temperate tree seedling leaf-out phenology and canopy close phenology in response to environmental drivers and used climate change projections to forecast changes to the duration of spring phenological escape. We then used these predictions to estimate changes in annual carbon assimilation while accounting for reduced carbon assimilation rates associated with hotter and drier summers. Lastly, we applied these estimates to previously published models of seedling growth and survival to investigate the net effect on seedling demographic performance. Our models predict that temperate tree seedlings will experience improved phenological escape and, therefore, increased spring carbon assimilation under climate change conditions. However, increased summer respiration costs will offset the gains in spring under extreme climate change leading to a net loss in annual carbon assimilation and demographic performance. Furthermore, we found that annual carbon assimilation predictions depend strongly on the species of nearby canopy tree that seedlings were planted near, with all seedlings projected to assimilate less carbon (and therefore experience worse demographic performance) when planted near Quercus rubra canopy trees as opposed to Acer saccharum canopy trees. We conclude that changes to spring phenological escape will have important effects on how tree seedling recruitment is affected by climate change, with the magnitude of these effects dependent upon climate change severity and biological interactions with neighboring adults. Thus, future studies of temperate forest recruitment should account for phenological escape dynamics in their models.
物候逃离是一种策略，落叶林下植物通过在树冠关闭之前提前落叶来获取直接阳光，这在塑造温带树种幼苗的繁殖方面起着重要作用。先前的研究已经调查了气候变化将如何改变草本物种的这些动态，但对于像树种幼苗这样的木本物种将如何受到影响，存在知识空白。在这里，我们模拟了温带树种幼苗展叶和树冠关闭的物候，以响应环境驱动因素，并利用气候变化预测来预测春季物候逃离持续时间的变化。然后，我们使用这些预测来估计年度碳同化量的变化，同时考虑到与更热、更干燥的夏季相关的碳同化率降低。最后，我们将这些估计应用于之前发表的幼苗生长和存活模型中，以调查对幼苗种群表现的净影响。我们的模型预测，温带树种幼苗将在气候变化条件下经历更好的物候逃离，因此春季碳同化量增加。然而，夏季呼吸成本的增加将抵消极端气候变化下春季的收益，导致年度碳同化量和种群表现的净损失。此外，我们发现，年度碳同化量的预测强烈依赖于幼苗附近树冠树种的种类，与种植在 Acer saccharum 树冠树下的幼苗相比，所有幼苗在种植在 Quercus rubra 树冠树下时预计会同化更少的碳（因此表现出更差的种群表现）。我们得出的结论是，春季物候逃离的变化将对气候变化如何影响树种幼苗的繁殖产生重要影响，这些影响的程度取决于气候变化的严重程度以及与邻近成年个体的生物相互作用。因此，未来的温带森林繁殖研究应该在其模型中考虑物候逃离动态。
