New insights of global vegetation structural properties through an analysis of canopy clumping index, fractional vegetation cover, and leaf area index

Abstract

Canopy clumping index (CI), fractional vegetation cover (FVC), and leaf area index (LAI) are important vegetation structural variables. Characterization of the spatial and temporal variations of these variables is important for understanding the global vegetation properties, canopy radiative transfer processes, and land surface modeling studies. This study explores the global CI, FVC, and LAI and their relationships using currently available global products from 2003−2017: CAS-CI (V1.1), GEOV2 FVC, and MODIS LAI (C6.0). The results show that global FVC and LAI have increased, whereas CI has slightly decreased since 2003. CI shows a negative relationship with both FVC and LAI. The specific vegetation cover (SVC), defined as the ratio of FVC to LAI, shows distinct spatial and temporal patterns for different land cover types and has great potential for vegetation characterization and phenology studies. The base and full CIs, calculated as the CI values during leaf emergence and full ground coverage or maximum LAI, respectively, were proposed to determine the seasonal variations in CI for different vegetation types. A global monthly leaf projection function (G(0)) map was generated for the first time to characterize the leaf angular distribution. Overall, this study enhances our understanding of the global CI, FVC, and LAI and provides new insights on characterizing the biophysical properties of global vegetation. These findings are important for canopy reflectance modeling and parameter retrieval studies.