Nutrients in litterfall represent important fluxes to the soil and may vary with climate and soil attributes. Long-term studies of these fluxes in tropical dry forests (TDF) are scarce despite their relevance to understand the response of litterfall nutrients to rainfall, the controlling driver for ecosystem dynamics in TDF and which is like to vary with climate change. The main objective of this work was to study the variation in litterfall nutrients (C, N and P) over a period of 8 years with contrasting precipitation and among different sites located within small watersheds in the landscape. This information should provide elements to understand the sensitivity of these fluxes to such factors and to determine the degree to which N and P fluxes differ in their response to temporal and spatial variability. All litterfall samples were collected in the Chamela-Cuixmala Reserve in the state of Jalisco, Mexico, which is dominated by tropical dry forest, as part of a long-term research project. Most species in the forest lose their leaves during the extended dry season. Sites were located in permanent quadrats within five small watersheds, where litterfall has been collected since 1983. Data for this study comprise the period between 1995 and 2003. Individual samples were pooled to represent three phenological seasons: dry (March-June), wet (July-October) and transition (November-February). Total nitrogen (N) and phosphorus (P) were determined by a semi-Kjeldhal method, while carbon was determined by combustion.
Results/Conclusions Mean C, N, P concentrations averaged over years and sites were 45.61%, 17.9 mg/g and 1.60 mg/g, respectively. Litterfall C did not vary significantly between seasons, among years and among sites (coefficients of variation were between 2 and 5 %). Litterfall N ranged between 6.7 mg/g and 38.9 mg/g but did not change among years with contrasting precipitation. Seasonally, it changed from 21.6 mg/g in the rainy season to 15.6 mg/g in the transition period, but concentrations did not differ among sites. Litterfall P ranged between 0.34 mg/g and 5.39 mg/g, with the lowest values recorded in the driest years (e.g. 1.12 mg/g in 2000) and in the dry season (0.96 mg/g). High litterfall P occurred in wet years (e.g. 2.7 mg/g in 1998) and during the rainy season (2.4 mg/g). In contrast to N, litterfall P differed among sites. Litterfall P concentration seems more sensitive than N to variation in rainfall and to site differences.
