Effects of forest-pasture edge on C,N and P associated with <Emphasis Type="Italic">Caesalpinia eriostachys</Emphasis>, a dominant tree species in a tropical deciduous forest in Mexico

Forest fragmentation in tropical ecosystems can alter nutrient cycling in diverse ways. We have analysed the effects of the forest-pasture edge on nutrient soil dynamics in a tropical deciduous forest (TDF) in Mexico. In two remnant forest fragments, both larger than 10 ha, litterfall, litter and soil samples associated to the tree Caesalpinia eriostachys were collected at five distances from the pasture edge into the inner forest (10 m in the pasture and 0–10, 30–40, 70–80 and 100–110 m towards the forest interior). We measured the concentrations of carbon (C), nitrogen (N) and phosphorus (P) in litterfall, surface litter and soil, and soil microbial C (C_mic) and microbial N (N_mic). Soil nutrient concentrations and C_mic and N_mic were lower in the pasture soils than in the forest soil samples. Total C and N pools, and C_mic and N_mic in the pasture were lower than in the forest. In contrast, net N immobilization and the increase in N_mic from rain to dry season increased from the edge to the inner forest. Soil P concentration was lower in the pasture and at the first distance class in the forest margin (0–10 m) than in the sites located further into the forest, while litter P concentration had the inverse pattern. Litterfall P was also reduced near the edge and increased towards the forest interior. As a consequence, litterfall C:P and N:P ratios decreased from the edge to the inner forest. These results suggest that the forest–pasture edge disrupts P dynamics within the first 10 m in the forest. Thus, plants' use of nutrients and productivity could be altered in the edge of fragmented forests.