Shrubs Compensate for Tree Leaf Area Variation and Influence Vegetation Indices in Post‐Fire Siberian Larch Forests
Shrubs Compensate for Tree Leaf Area Variation and Influence Vegetation Indices in Post‐Fire Siberian Larch Forests
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DOI：
10.1029/2022jg007107
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发表时间：
2023-02
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影响因子：
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通讯作者：
Nadav S. Bendavid;H. Alexander;S. Davydov;Heather Kropp;M. Mack;S. Natali;Seth A. Spawn‐Lee;
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文献类型：
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作者：
Nadav S. Bendavid;H. Alexander;S. Davydov;Heather Kropp;M. Mack;S. Natali;Seth A. Spawn‐Lee;
在火灾后的西伯利亚落叶松森林中，树木密度在燃烧范围内会有所不同，灌木构成了植被冠层的很大一部分。叶面积指数（LAI）定义为每单位地表面积的单侧总绿叶面积，可用于表征植物冠层的变化。我们利用异速生长法估算了 26 个地点的树木和高大灌木（>0.5 和 <1.5 m）的 LAI，这些地点具有不同的树干密度（0.05-3.3 茎/平方米）和树冠覆盖度（4.6%-76.9%），这些地点位于约 75 年前火灾后再生的年龄一致的成熟西伯利亚落叶松森林中。我们研究了树木密度、树木 LAI 和高灌木 LAI 之间的关系，以及 LAI 与归一化差异和增强植被指数（NDVI 和 EVI）卫星观测值之间的关系。在密度梯度上，树木 LAI 随着树木密度的增加而增加，而高灌木 LAI 则减少，乔木-灌木组合 LAI 没有表现出任何模式。我们还从 PlanetScope 和 Landsat 图像中发现高灌木 LAI 和 NDVI/EVI 之间存在显着的正相关关系。这些发现表明，高大的灌木补偿了树冠间隙中较低的树木 LAI，形成了在密度梯度上具有连续组合的乔木-灌木 LAI 的树冠。我们的研究结果表明，在这些生态系统中，NDVI 和 EVI 对高灌木冠层的变化比乔木冠层或混合树冠层的变化更敏感。这些结果提高了我们对森林密度与树木和灌木叶面积之间关系的理解，并对解释西伯利亚北方森林 LAI、NDVI 和 EVI 的空间变异具有重要意义。
In post‐fire Siberian larch forests, where tree density can vary within a burn perimeter, shrubs constitute a substantial portion of the vegetation canopy. Leaf area index (LAI), defined as the one‐sided total green leaf area per unit ground surface area, is useful for characterizing variation in plant canopies. We estimated LAI with allometry for trees and tall shrubs (>0.5 and <1.5 m) across 26 sites with varying tree stem density (0.05–3.3 stems/m2) and canopy cover (4.6%–76.9%) in a uniformly‐aged mature Siberian larch forest that regenerated following a fire ∼75 years ago. We investigated relationships between tree density, tree LAI, and tall shrub LAI, and between LAI and satellite observations of Normalized Difference and Enhanced Vegetation Indices (NDVI and EVI). Across the density gradient, tree LAI increases with increasing tree density, while tall shrub LAI decreases, exhibiting no patterns in combined tree‐shrub LAI. We also found significant positive relationships between tall shrub LAI and NDVI/EVI from PlanetScope and Landsat imagery. These findings suggest that tall shrubs compensate for lower tree LAI in tree canopy gaps, forming a canopy with contiguous combined tree‐shrub LAI across the density gradient. Our findings suggest that NDVI and EVI are more sensitive to variation in tall shrub canopies than variation in tree canopies or combined tree‐shrub canopies in these ecosystems. The results improve our understanding of the relationships between forest density and tree and shrub leaf area and have implications for interpreting spatial variability in LAI, NDVI, and EVI in Siberian boreal forests.