Reframing tropical savannization: linking changes in canopy structure to energy balance alterations that impact climate
Reframing tropical savannization: linking changes in canopy structure to energy balance alterations that impact climate
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DOI：
10.1002/ecs2.3231
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发表时间：
2020-09
期刊：
影响因子：
2.7
通讯作者：
S. Stark;D. Breshears;S. Aragón;J. C. Villegas;D. Law;Marielle N. Smith;D. Minor;R. Assis;D. R. Almeida;G. Oliveira;S. Saleska;A. Swann;J. Moura;J. Camargo;R. Silva;L. Aragão;R. Oliveira
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文献类型：
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作者：
S. Stark;D. Breshears;S. Aragón;J. C. Villegas;D. Law;Marielle N. Smith;D. Minor;R. Assis;D. R. Almeida;G. Oliveira;S. Saleska;A. Swann;J. Moura;J. Camargo;R. Silva;L. Aragão;R. Oliveira
由于森林砍伐、火灾和干旱的干扰，热带生态系统正在以前所未有的速度退化。这些干扰的集体效应可能会使亚马逊森林等大部分热带生态系统通过树木损失、功能变化和火灾的出现（草原化）转变为类似热带草原的结构。从森林状态到更开放的稀树草原状结构的变化可以影响当地的小气候，表面能量通量和生物圈-大气相互作用。生态系统状态变化的一个主要类型是受干扰森林中树木覆盖和结构复杂性的损失。虽然在对比历史上不同的原始森林和稀树草原系统之间的能量通量方面取得了重要进展，但次生林和稀树草原样生态系统的出现需要重新考虑树木结构的梯度，这些梯度在多个尺度上跨越森林和稀树草原样状态。在这个创新的观点，我们借鉴森林草原连续体的文献，开发一个框架来评估热带森林退化对地表能量通量和冠层结构的后果。我们用对比的林冠结构来说明这个框架，这些林冠结构从简单的、开放的、稀树草原状的到复杂的、封闭的，代表热带潮湿森林的，在亚马逊的两个气候不同的地区。使用最近开发的快速实地评估方法，我们量化了相邻站点之间的覆盖，叶面积垂直分布，表面粗糙度，辐射和能量平衡分配的差异，并将冠层结构与相邻的老森林进行比较;结构更简单的森林显示出较低的净辐射。为了解决森林-大气反馈，我们还考虑了冠层结构变化对未来额外干扰敏感性的影响。我们说明了一个匡威过渡恢复结构干扰测量森林冠层结构10年后，在突破性的Seca Floresta实验中施加5年的干旱。我们的方法战略上使快速表征相关的植被模型退化后的表面特性，并推进表面特性和冠层结构变量之间的联系，越来越多地从遥感。最后，我们假设，了解退化热带森林状态的地表能量平衡和小气候变化不仅揭示了关键的大气强迫，而且还揭示了森林敏感性对额外气候相关干扰的关键局部尺度反馈。
Tropical ecosystems are undergoing unprecedented rates of degradation from deforestation, fire, and drought disturbances. The collective effects of these disturbances threaten to shift large portions of tropical ecosystems such as Amazon forests into savanna‐like structure via tree loss, functional changes, and the emergence of fire (savannization). Changes from forest states to a more open savanna‐like structure can affect local microclimates, surface energy fluxes, and biosphere–atmosphere interactions. A predominant type of ecosystem state change is the loss of tree cover and structural complexity in disturbed forest. Although important advances have been made contrasting energy fluxes between historically distinct old‐growth forest and savanna systems, the emergence of secondary forests and savanna‐like ecosystems necessitates a reframing to consider gradients of tree structure that span forest to savanna‐like states at multiple scales. In this Innovative Viewpoint, we draw from the literature on forest–grassland continua to develop a framework to assess the consequences of tropical forest degradation on surface energy fluxes and canopy structure. We illustrate this framework for forest sites with contrasting canopy structure that ranges from simple, open, and savanna‐like to complex and closed, representative of tropical wet forest, within two climatically distinct regions in the Amazon. Using a recently developed rapid field assessment approach, we quantify differences in cover, leaf area vertical profiles, surface roughness, albedo, and energy balance partitioning between adjacent sites and compare canopy structure with adjacent old‐growth forest; more structurally simple forests displayed lower net radiation. To address forest–atmosphere feedback, we also consider the effects of canopy structure change on susceptibility to additional future disturbance. We illustrate a converse transition—recovery in structure following disturbance—measuring forest canopy structure 10 yr after the imposition of a 5‐yr drought in the ground‐breaking Seca Floresta experiment. Our approach strategically enables rapid characterization of surface properties relevant to vegetation models following degradation, and advances links between surface properties and canopy structure variables, increasingly available from remote sensing. Concluding, we hypothesize that understanding surface energy balance and microclimate change across degraded tropical forest states not only reveals critical atmospheric forcing, but also critical local‐scale feedbacks from forest sensitivity to additional climate‐linked disturbance.