Conservation Ecology Center, Smithsonian's National Zoo & Conservation Biology Institute, Front Royal, VA, 22630, USA.
Department of Ecology and Evolutionary Biology, UCLA, Los Angeles, CA, 90039, USA.
New Phytol. 2023 Jan;237(1):22-47. doi: 10.1111/nph.18539.
Rising temperatures are influencing forests on many scales, with potentially strong variation vertically across forest strata. Using published research and new analyses, we evaluate how microclimate and leaf temperatures, traits, and gas exchange vary vertically in forests, shaping tree, and ecosystem ecology. In closed-canopy forests, upper canopy leaves are exposed to the highest solar radiation and evaporative demand, which can elevate leaf temperature (T ), particularly when transpirational cooling is curtailed by limited stomatal conductance. However, foliar traits also vary across height or light gradients, partially mitigating and protecting against the elevation of upper canopy T . Leaf metabolism generally increases with height across the vertical gradient, yet differences in thermal sensitivity across the gradient appear modest. Scaling from leaves to trees, canopy trees have higher absolute metabolic capacity and growth, yet are more vulnerable to drought and damaging T than their smaller counterparts, particularly under climate change. By contrast, understory trees experience fewer extreme high T 's but have fewer cooling mechanisms and thus may be strongly impacted by warming under some conditions, particularly when exposed to a harsher microenvironment through canopy disturbance. As the climate changes, integrating the patterns and mechanisms reviewed here into models will be critical to forecasting forest-climate feedback.
气温上升正在多方面影响森林，在森林层次结构中垂直方向上可能存在强烈的变化。利用已发表的研究和新的分析，我们评估了微气候和叶片温度、特征以及气体交换如何在森林中垂直变化，从而影响树木和生态系统的生态。在封闭林冠的森林中，上层树冠叶片暴露在最高的太阳辐射和蒸发需求下，这会导致叶片温度（T）升高，特别是当蒸腾冷却受到有限的气孔导度限制时。然而，叶片特征也会随着高度或光梯度的变化而变化，部分缓解并防止上层树冠 T 的升高。叶片代谢通常会随着垂直梯度的升高而增加，但在梯度上的热敏感性差异似乎不大。从叶片到树木的尺度上，冠层树木具有更高的绝对代谢能力和生长，但比它们的小型对应物更容易受到干旱和高温的伤害，特别是在气候变化下。相比之下，林下树木经历的极端高温较少，但冷却机制较少，因此在某些条件下可能会受到变暖的强烈影响，特别是当它们通过林冠干扰暴露在更恶劣的微环境中时。随着气候的变化，将这里综述的模式和机制整合到模型中对于预测森林-气候反馈至关重要。
