Aspects of rain forest nutrient dynamics at Los Tuxtlas, Mexico.

Several aspects of nutrient cycling were studied in the Lowland Tropical Rain Forest at Los Tuxtlas. This is at (18° 34' - 18° 36’ N, 95° 04' - 95° 09' W) and represents the northernmost extension of the rain forest Formation in the New World. The relationships among the forest structure, small litterfall production (22 months), small litterfall element concentrations, and soil nutrients were investigated. The degree of nutrient resorption between fresh and dehisced leaves was evaluated for several tree species. \nThe forest had a preponderance of mesophylls, a relatively low tree species diversity, basal area, and small litterfall production. An estimation of leaf litterfall contribution was provided for 119 woody species and the temporal variation of the leaf litterfall was described. Soil nutrient concentrations were high probably owing to the volcanic eruption of 1793. Nutrient-element concentrations were relatively high in the small litterfall and fresh leaves, and nutrient resorption was relatively low. \nThe soil nutrient concentrations in pastures of 12, 32, and 52 years of age were compared with the forest and were relatively high in spite of their maintaining a high density of cattle. \nThe soil under isolated trees in the pastures had higher nutrient concentrations than the open pastures. There was a higher diversity of seedling species under the isolated trees but a growth experiment in a tree nursery did not show differences among the soils from the undisturbed forest, open-pastures and under the isolated trees. It seems that soil nutrients are always high at Los Tuxtlas and override any effect of nutrient addition by the isolated trees.