Effects of canopy gaps, topography, and soils on the distribution of woody species in a central Brazilian deciduous dry forest

The interrelationships between the distribution of woody species and environmental variables were investigated in an area of deciduous dry forest in Santa Vitoria, central Brazil. This is the first study of a vanishing type of dry forest which grows on base-rich soils originating from the basalt bedrocks of southern Goias and western Minas Gerais. A survey of topography, soil properties, canopy gaps and woody plants (greater than or equal to 5 cm diameter at the base of the stem) was conducted in 50-15 x 15 m quadrats. The soils were classified into the following soil series: Hapludolls --> Haplustolls --> Ustropepts --> Rhodustalfs. This series corresponded ro a gradient of increasing elevation and effective soil depth and decreasing slope gradient, soil organic matter and total exchangeable bases. A canonical correspondence analysis and a detrended correspondence analysis indicated that plant species' abundance distribution was significantly correlated with both the relative area of canopy gaps in the quadrats and the soil-topography gradient. Presumably, the critical factors involved in these two gradients are, respectively light and ground water regimes. The influence of canopy gaps (i.e., light) was surprising and has nor been documented previously for tropical deciduous dry forests.