PARENT SESSION
Monday, August 7, 5:00-6:30 pm
Poster Session 5 - Landscape and ecosystem ecology
Exhibit Hall, Ballroom Level, Cook Convention Center

Does history make the difference?: Land use practices and the ever-changing tropical dry forest of Sonora, Mexico.

Alvarez-Yepis, Juan Carlos^*,1, Martinez-Yrizar, Angelina¹, ¹ Institute of Ecology, UNAM, Hermosillo, Sonora, Mexico

ABSTRACT- The tropical dry forest ecosystem under different land-use histories in Alamos, northwestern Mexico, was studied to evaluate the effects of anthropogenic disturbance on forest diversity and structure. Four land-use categories were compared: three of preserved forest (PF) with light, moderate and heavy grazing, respectively, and one of 30-yr secondary forest with occasional grazing (SF). On each category, three 0.1 ha sampling plots were established as replicates, all individuals DBH≥2.0 cm identified, and measured for total height and stem diameter. Basal area was used to estimate aboveground biomass. Three composite soil samples per plot were collected for chemical analysis. Cation exchange capacity was significantly lower in SF, but N and organic matter contents significantly higher in PF+moderate grazing. A total of 4,608 live stems, accounting for 2,077 individuals were measured; 46.7% were multi-stemmed. Forty-two morphospecies from 17 families were recorded, Fabaceae the best represented. Species density was significantly lower, and dominance significantly higher in SF. Basal area and biomass were significantly higher in PF+moderate grazing. CCA showed CEC is highly correlated with the actual species distribution in the study area. Our basal area, density of individuals and species values broaden the lower limits of the ranges reported for a large group of Mexican tropical dry forests. Despite of chronic disturbance, sprouting could have contributed to maintain, in the preserved forest sites, the characteristics typical of a mature forest. Secondary forests, expanding rapidly, deserve conservation attention due to their capacity to accumulate organic matter in a relatively short time, which reflects their potential for carbon storage.

Key words: ecosystem ecology, land-use change, tropical dry forest