MODELLING VEGETATION DIVERSITY TYPES IN MEXICO BASED UPON TOPOGRAPHIC FEATURES

摘要

The role played by topography as a surrogate variable to explain vegetation diversity types (VDT) was evaluated. Using GIS, a Simpson vegetation diversity index for the entire Mexican territory was computed based on land use and vegetation maps. Then, the correlation between VDT and topographical attributes (elevation, range of elevation, slope, roughness and diversity of aspect) was calculated using different sizes of analysis windows. A significant correlation between topographical variables and vegetation diversity was found (Spearman coefficient of correlation > 0.4, p=0.01 with three variables: elevation average and range, and slope), with an optimal window of 80 × 80km~2. Subsequently, modeling VDT from the topographical attributes using an artificial neural network approach was attempted. The comparison between the modeled and the observed VDT maps showed that the model produced a reasonable estimate of vegetation diversity. From error analysis it may be deduced that VDT cannot be totally explained by topographical attributes alone, although these play a primary role in VDT at regional to continental scale. As results have shown that land cover and vegetation accurately portrays biodiversity distribution patterns, VDT modeling is a promising approach to assess biodiversity. It is concluded that topographical variables, globally available at a 3-arc-second resolution (～90m) through the Shuttle Radar Topography Mission (SRTM) project, may be used to portray regional biodiversity patterns. This is crucial in tropical countries that harbor high biodiversity but often lack accurate and updated land cover databases.