The decomposition of Iitter in grasslands of northern Mexico: a comparison between arid and non-arid environments

The mass loss of grass litter was studied in two climatically contrasred zones: the Bolson de Mapimi (Chihuahuan Desert, annual rainfall 271 mm) and La Michilia (Western Sierra Madre pine-oak forest, annual rainfall 788 mm). Plastic grass litter bags were placed on the ground and collected periodically over 29 months, dried, weighed and analysed for carbon and nitrogen. The dry mass data were fitted to time, rainfall and temperature as independent variables, using differential equation models that assume constant or variable decomposition rates. The overall velocity of decomposition was strongly correlated with the proportion of leaves and stems in the initial litter. In La Michilia, decomposition rates decreased as the litter disappeared. Weight loss was found to be associated more with temperarure and rainfall than with time, and the C:N ratio decreased strongly as decomposition progressed. In Mapimi, on the other hand, decompo-sition rates did not decrease so strongly as litter disappeared; rime was found TO be an adequate predictor of mass loss, and the C:N ratio was more consrant. It is concluded that abiotic factors (physical weathering) are responsible for a large portion of the mass loss of grass litter in and environments