Abstract: By using cyclic sampling method, the aboveground biomass and leaf area index (LAI) of typical grassland in tower flux footprint were measured at three growth stages, i.e., early July (July 2-7), late July (July 20-26), and late August (Aug. 25-30), with their spatial patterns analyzed by geostatistics. At the three stages, the aboveground biomass of the grassland kept rising, while the LAI decreased after an initial increase. Both the two variables had good spatial autocorrelation, with similar spatial pattern and temporal evolution trend, and changed from stripe to patch. From early July to late August, the C₀/(C₀+C) of the aboveground biomass and LAI all decreased significantly, indicating that the spatial autocorrelation of the two variables changed from medium to high. The change ranges of the two variables gradually decreased, presenting the decrease of spatial continuity. The fractal dimension (D) also decreased gradually, suggesting the increase of spatial dependence. Topography and field management were the main factors affecting the spatial distribution of aboveground biomass and LAI, which induced the spatial variability of water and heat, and further, affected the grass growth.

Key words: LAI, biomass, cyclic sampling, geostatistics, grassland