Investigating the relationship between NDVI and LAI in semi-arid grassland in Inner Mongolia using in-situ measurements

Leaf area index (LAI) is a key variable functionally related to plant biomass production. Accurate estimation of LAI is important for monitoring vegetation dynamics, and LAI information is essentially required for the prediction of microclimate and various biophysical processes within and below canopy. The traditional, direct and destructive method of measuring LAI is time-consuming. Modern gap fraction technique can assess LAI fast and easily, however its application is problematic with vegetations of low stature. Alternatively, NDVI (Normalized Difference Vegetation Index) as a widely used spectral reflectance index has been shown to be a good estimator of LAI and is used to estimate LAI indirectly. In situ measurements of NDVI and LAI at three sites in semi-arid grassland in Inner Mongolia, China were carried out during the growing season in 2005 and 2006. Based on these sites, a general linear and a general exponential relationship (LAI = -0.0897 + 1.424 * NDVI, R = 0.79; LAI = 0.128 * exp(NDVI/0.311), R = 0.77) were developed, which can be used for various grazing intensity grasslands and also for higher vegetation cover area (e.g. wetland) in the region. These equations for estimating LAI are suitable for the natural range of vegetation in this area during the growing season under both normal and dry weather conditions. By simply applying NDVI measurements and these relationships, the vegetation status and grass yield in the area will be rapidly and nondestructively estimated, which is helpful for livestock management and sustainable land use.