Plant diversity in highly fragmented forest landscapes in Mexico and Chile: implications for conservation.

Abstract

AbstractResearch addressed a range of issues relating to the regional determinants of species diversity, the effects of fragmentation and human disturbance on tree diversity at different spatial scales, changes of diversity along secondary succession after deforestation, and plausible future scenarios of species decline associated with continued habitat loss across a variety of ecological and socio-economic conditions in Latin America. This analysis was performed using different woody vegetation datasets in combination with various field measurements, remote sensing and GIS data. Regionally, climatic factors emerged as primary predictors of tree diversity. At finer scales, fragmentation and human disturbance better explained patterns of species diversity. These effects were, however, dependent on the time after fragmentation occurred. In the short term, habitat fragmentation was not likely to reduce the overall diversity of a fragment, but could have a slight positive effect on local diversity within fragments. Moreover, we detected a negative effect of human disturbance that far outweighed the effects of fragmentation at this scale. In the long term, however, fragmentation was found to significantly reduce the overall diversity of forest remnants. Patterns of diversity along chronosequences of abandoned pastures and croplands were consistent across all study areas in Mexico and suggested that vegetation structure and community composition gradually come to mirror those of mature forests. However, species richness strongly depended upon the functional type under consideration. Using ground-based floristic inventories and forest loss rates derived from satellite imagery, we estimated the percentage of species most likely to disappear, or at least become seriously threatened with extirpation, assuming continued habitat loss until 2025. Alarmingly, the predicted species decline in the Highlands of Chiapas was over 40% using estimated yearly deforestation rates of 4.8%.