Relation between leaf area index and NDVI for subarctic deciduous vegetation.

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. [ABSTRACT FROM AUTHOR]