Resumen

LAWRENCE, Deborah  y  FOSTER, David. changes in forest biomass, litter dynamics and soils following shifting cultivation in southern mexico: an overview. INCI [online]. 2002, vol.27, n.8, pp.400-408. ISSN 0378-1844.

Sampling along natural and human-made gradients, we evaluated the relative impact of broad environmental drivers and stand-level effects of land use on ecosystem processes in a dry tropical forest of the southern Yucatan peninsula. The objectives were to 1) describe natural environmental gradients in precipitation and soils at the regional scale, 2) explore the response of key ecosystem properties and processes to these gradients, and 3) understand the effects of forest age on stands within a given region of the gradient. Aboveground biomass (live and detrital), litter production and chemistry, and soils were studied. Ten to 13 stands, including secondary and mature forests, were sampled in each of 3 sites spanning a highly seasonal rainfall gradient of 900-1400 mm/yr. Litterfall increased and litter nutrient concentrations decreased at the peak of the dry season. In mature forest, environmental factors associated with the precipitation gradient did constrain litter production, forest floor mass and soil organic matter. To understand differences in the live aboveground biomass of mature forests, the human history of the area added critical information, including logging history and decisions about untouched areas (e.g. upper slopes). All aspects of structure and function in young secondary forests (live aboveground biomass, litter production, forest floor mass, and critical soil properties) are strongly influenced by the age of the stand. Recovery to current mature forest levels is conservatively estimated to take 55-95 years. P and/or N seem to limit essential ecosystem processes, such as litter production, decomposition and aboveground biomass. We suggest that once water limitation is alleviated, P becomes limiting. Evidence includes greater reabsorption of P from litter, a strong response to the precipitation gradient of P but not N concentration and total inputs, and an increase in P-use efficiency with increasing stand age. The presence of humans in the Southern Yucatan results in ecosystem changes that are greater than those induced by natural, environmental variation at the regional scale. For the best understanding of these landscapes, and for scaling up from case studies to regional and global assessments, integrating human impacts on ecosystem processes is vital.

Palabras clave : Nutrient Cycling ; Land Use Change ; Forest Recovery ; Phosphorus ; Nitrogen .