No evidence for fractal scaling in canopy surfaces across a diverse range of forest types
No evidence for fractal scaling in canopy surfaces across a diverse range of forest types
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DOI：
10.1111/1365-2745.14244
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发表时间：
2023-12
影响因子：
5.5
通讯作者：
F. Fischer;T. Jucker
中科院分区：
文献类型：
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作者：
F. Fischer;T. Jucker
冠层结构复杂性是森林生态系统的一个关键的新兴特性，直接关系到它们储存碳、循环水和养分以及为生物多样性提供栖息地的能力。然而，我们缺乏一个通用的框架来量化森林冠层的结构复杂性，如果有简单的规则来解释我们在世界各地的森林中观察到的冠层结构的巨大变化，还有待观察。表征森林生态系统结构复杂性差异的一个主要候选者是分形标度律，或统计自相似性的度量。如果森林冠层在本质上是分形的，那么它们的结构属性可以被提炼成一个单一的系数--它们的分形维数--然后可以用来直接比较生物群落内部和之间的结构差异。为了验证这一想法，我们使用了在澳大利亚九个景观中获得的机载激光扫描（ALS）数据，这些景观跨越了巨大的环境梯度，包括从干燥的灌木丛，热带稀树草原，茂密的雨林到90米高的山灰森林。使用ALS数据，我们建立了每个景观的高分辨率3D冠层高度模型，以便我们可以量化它们遵循分形标度律的程度，基于一套全面的分形维数估计。在所有生态系统类型中，分形尺度假设一直被违反，真实的世界森林冠层和模拟分形表面之间存在明显和系统的差异。然而，与分形的偏差确实在不同地点之间存在可预测的差异，在干旱程度较低的环境中，森林以高大的树木为主，树冠较大，在各个尺度上表现出较高的自相似性。综合：我们的研究结论表明，冠层表面不分形超出了个别树冠的规模。尽管如此，我们仍然观察到了具有生态意义和可推广的森林结构模式，这些模式密切反映了树木大小和结构的生物物理和生理限制。这些模式指向一个更一般的框架来描述生态复杂性。
Canopy structural complexity is a key emergent property of forest ecosystems that directly relates to their ability to store carbon, cycle water and nutrients, and provide habitat for biodiversity. However, we lack a general framework for quantifying the structural complexity of forest canopies, and it remains to be seen if there are simple rules that explain the huge variation in canopy structure that we observe across the world's forests. A leading candidate for characterizing differences in structural complexity among forest ecosystems are fractal scaling laws, or measures of statistical self‐similarity. If forest canopies were fractal in nature, their structural attributes could be distilled into a single coefficient—their fractal dimension—which could then be used to directly compare structural differences within and across biomes. To test this idea, we used airborne laser scanning (ALS) data acquired across nine landscapes in Australia that span a huge environmental gradient and include everything from dry shrublands, tropical savannas, dense rainforests, to 90 m tall Mountain Ash forests. Using the ALS data, we built high‐resolution 3D canopy height models of each landscape so that we could quantify how closely they followed fractal scaling laws, based on a comprehensive set of fractal dimension estimators. Across all ecosystem types, fractal scaling assumptions were consistently violated, with clear and systematic differences between real‐world forest canopies and simulated fractal surfaces. However, deviations from fractality did vary predictably among sites, with forests in less arid environments, dominated by tall trees with large crowns, exhibiting a higher degree of self‐similarity across scales. Synthesis: Our study conclusively shows that canopy surfaces are not fractal beyond the scale of individual tree crowns. Nevertheless, we still observed ecologically meaningful and generalisable patterns in forest structure across scales, which closely reflect biophysical and physiological constraints on tree size and architecture. These patterns point the way towards a more general framework for characterizing ecological complexity.