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 ²m ^‑2. 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 ² m ^‑2 (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 ² m ^‑2 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 ² and 0.9 ± 0.1 m ² m ^‑2, respectively), but much higher values in 1992 (2.7 ± 0.2 m ² m ^‑2). The difference is probably attributed to an atypical rainfall event in January 1992 (644 mm), which retarded leaf abscission.