Testing patterns of zonation in mangroves: scale dependence and environmental correlates in the Sundarbans of Bangladesh

1 Associations between abiotic variables and patterns of species distributi on and abundance are a major preoccupation of community ecologists. In many habitats, this association is manifest in discrete zones of vegetation. 2 We used statistical methods to examine tree species distribution patterns in relatively undisturbed regions of the Sundarbans of Bangladesh. We test ed the hypothesis that mangroves occur in discrete zones with respect to el evation. These data were gathered with explicit attention to local and regi onal differences in edaphic characteristics so that species-environment rel ationships could be analysed at several spatial scales. 3 Correlations were also assessed between mangrove species composition and edaphic variables that co-vary with elevation, i.e. salinity, field capacit y, cation exchange capacity, percentage silt, and mangrove physiognomic cat egory (slope, basin, levee and flat). 4 Quantitative statistical analysis using randomization techniques failed t o detect species zonation along any of 33 individual 200-m transects, withi n 1-km(2) blocks, or within 1200-km(2) regions. 5 Canonical correspondence analysis relating edaphic variables to species d istributions accounted for a total of only 24% of the variance in species c omposition. 6 Our data suggest that the absence of zonation in the Bangladesh Sundarban s reflects the underlying biology of the system and is not an artefact of l ong-term human disturbance.