Seasonal changes of leaf area index (LAI) in a tropical deciduous forest in west Mexico

Light canopy transmittance and the Beer-Lambert equation were utilized to assess monthly leaf area index (LAI) of a tropical deciduous forest ecosystem on the west coast of Mexico. The light transmittance coefficient (k) was obtained by analyzing vertical leaf and light distribution in the forest canopy. An independent LAI estimate was obtained using litterfall data. The calculated k value was 0.610 ±0.035 (standard error). Average maximum LAI obtained with litterfall data was 4.2 + 0.4 m m~. There was a significant correlation (P< 0.001, r= 0.98) between litter-LAI estimations and those obtained with the Beer-Lambert equation. The regression explained 95% of the variation; however, light-LAI overestimated litter-LAI by a constant of 0.87±0.12 m m~ (the slope was 1.03 and Y intercept was 0.87). The discrepancy is partially attributed to leaf retention of the few evergreen species, and perhaps leaf retention of a few deciduous species beyond the end of the litterfall collection. Maximum annual LAI was similar in both study years (4.5±0.3 m m~ in 1990 and 4.9±0.4 in 1991). Minimum LAI showed considerable variation between years with similar values in the dry seasons of 1990 and 1991 (1.0 ±0.1 m and 0.9 + 0.1 m mr, respectively), but much higher values in 1992 (2.7 + 0.2 m m~). The difference is probably attributed to an atypical rainfall event in January 1992 (644 mm), which retarded leaf abscission.