ABSTRACT We consider the relationship between leaf area index (LAI) and normalized difference vegetation index (NDVI) for green-leaf vegetation from a subarctic study site, specifically to test whether relationships optimized for lower-latitude vegetation can be assumed to hold at higher latitudes. We focus attention particularly on dwarf-shrub vegetation, which has received little previous investigation. We have collected hyperspectral measurements of the optical properties (reflectance and absorptance) of single leaves from dwarf shrub and tree species common to northern European Russia, and have developed a simple physical model of the properties of assemblages (‘leaf stacks’) of these leaves. The model is shown to provide a satisfactory explanation of the effect of varying the number of leaves in a stack on its NDVI, and can be easily adapted to make simple measurements using relatively inexpensive equipment. Our results show that the LAI-NDVI relationship for a vegetation canopy will saturate (approach within 10% of its limiting value) when the LAI reaches a value of around 2 to 3. Values this low are not uncommon in subarctic vegetation. It is also shown that dwarf shrub vegetation may show lower NDVI than trees for the same LAI.

中文翻译：

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亚北极落叶植被叶面积指数与NDVI的关系

摘要 我们考虑了来自亚北极研究地点的绿叶植被的叶面积指数 (LAI) 和归一化差异植被指数 (NDVI) 之间的关系，特别是为了测试是否可以假设为低纬度植被优化的关系在高纬度地区成立. 我们特别关注矮灌木植被，此前很少对其进行调查。我们收集了俄罗斯北欧常见的矮灌木和树种的单片叶子的光学特性（反射率和吸收率）的高光谱测量值，并开发了这些叶子组合（“叶叠”）特性的简单物理模型. 该模型显示出对改变堆栈中叶子数量对其 NDVI 的影响提供了令人满意的解释，并且可以很容易地适应使用相对便宜的设备进行简单的测量。我们的结果表明，当 LAI 达到 2 到 3 左右的值时，植被冠层的 LAI-NDVI 关系将饱和（接近其极限值的 10% 以内）。如此低的值在亚北极植被中并不少见。还表明，对于相同的 LAI，矮灌木植被的 NDVI 可能低于树木。