Leaf Decomposition in a Mexican Tropical Rain Forest

Abstract

Leaf decomposition in five common species was studied in the Los Tuxtlas tropical rain forest, Veracruz state, Mexico. The species were: Nectandra ambigens (Blake) C. K. Allen, Pseudolmedia oxyphyllaria Donn. Sm, Dussia mexicana (Standl.) Harms, Ficus yoponensis Desvaux and Poulsenia armata (Miq.) Standl. Two experimental studies were done using litter bags, one comparing flat and slope conditions, and the second one in closed canopy and gap conditions. In addition, decomposition was compared between the dry and rainy season. There were significant differences in decomposition rates between species and seasons, but not between zones (flat and gentle slope, and closed forest and gap conditions). The highest decomposition rates were observed for species with high nutrient contents, and also during the rainy season. The data were fitted to three mathematical models derived from the negative simple exponential; the double exponential model for decay was significant. Also, the negative, simple, exponential model which assumes that k is not constant, turned out to be significant for the experiment in closed canopy and gap conditions. RESUMEN Se estudio la descomposicion de cinco especies arboreas en una selva humeda tropical de Los Tuxtlas, Veracruz, Mexico. Las especies fueron: Nectandra ambigens (Blake) C. K. Allen, Pseudolmedia oxyphyllaria Donn. Sm, Dussia mexicana (Standl.) Harms, Ficus yoponensis Desvaux and Poulsenia armata (Miq.) Standl. Se utilizo el metodo de las bolsas de malla. Se Ilevaron a cabo dos experimentos, en el primero se compararon condiciones de plano y pendiente, y en el segundo se compararon selva bajo dosel y claros. Adema's, se comparo la descomposicion entre las temporadas seca y Iluviosa. Se observaron diferencias significativas en las tasas de descomposicion entre las especies y las epocas consideradas, pero no entre las zonas (plano y pendiente ligera, y dosel cerrado y claros). Las tasas de descomposicion mas altas se observaron en las especies con mas alta concentracion de nutrientes, y tambien en la temporada de Iluvias. Los datos se ajustaron a tres modelos matemaiticos derivados del exponencial negativo simple; solo fueron significativos el doble exponencial negativo y el exponencial negativo simple, que asume que k no es constante, para el experimento realizado en condiciones de dosel cerrado y claros.