Comparison of the Leaf Area Index (LAI) of Two Types of Dipterocarp Forest on the West Bank of the Mekong River, Cambodia

Leaf area index (LAI) is a key biophysical variable in most process-based models of forest ecosystems and water cycles. We compared the LAI of two types of tropical seasonal forest in Kampong Thom Province, Cambodia. The two forest types are extremes of crown-cover density, i.e., closed dry evergreen forest (DEF) and open dry deciduous forest (DDF), suggesting marked spatial variation in forest site conditions such as soil moisture. Monthly changes in LAI were estimated indirectly using a plant canopy analyzer and hemispherical photographs. Both methods of LAI estimation showed instrument errors, i.e., low reproducibility in the plant canopy analyzer data and LAI-saturation in hemispherical photograph data; nevertheless, LAI values differed between DEF and DDF. The average LAI from three years of measurements was about 4.6 times higher in DEF than in DDF. DDF exhibited much greater seasonality than DEF. The annual minimum LAI averaged 76% and 84% of the annual maximum LAI for DDF and DEF, respectively. LAI showed high peaks in the rainy season and decreased in the dry season. However, in DEF, LAI decreased twice annually, at the beginning of the dry season and the beginning of the rainy season. Seasonal changes in LAI could be approximated using a third-degree Fourier-series equation.