Within-plot relationships between tree species occurrences and hydrological soil constraints: an example in French Guiana investigated through canonical correlation analysis.

Spatial relationships between tree species and hydrological soilconstraints are analysed within a 10-ha rainforest plot at PistedeSt Elie in French Guiana. We used canonical correlation analysis to crossdirectly the occurrence-by-species table of 4 992 individuals (d.b.h. ≥10 cm) belonging to 120 species with qualitative soil variablesandquantitative spatial data. Firstly, the list of species occurrences wasconfronted to nine soildescriptors characterising a weathering sequence from the initial well-drainedferralitic cover to transformed hydromorphic soil conditions. This analysisrevealed that, apart from some specialised species restricted to the swampsthatexperience prolonged water saturation, the most abundant species can be orderedalong two intermingled gradients of tolerance limiting their niche amplitude: amain gradient of tolerance to prolonged water saturation that appears downslopeduring the weathering sequence; a second gradient of less importance,displayingthe species intolerant of prolonged water saturation according to theirtolerance to temporary confinement of the uphill transformed soil systems duetothe late appearance of a perched water-table. The results support thehypothesisthat at Piste de St Elie, the constraining soil conditions imposed by surfacewater saturation are more important determinants for tree zonation of many treespecies than water shortage. Secondly, the list of species occurrences wasconfronted to a spatialdata table built from a trend surface regression of the tree coordinates. Thisanalysis indicated that soil drainage is the main structuring factor of thelocal multispecies spatial pattern. After partialling out the soil effect, themultispecies pattern revealed a broader scale of heterogeneity that we supposedto be linked to endogenous factors resulting from population dynamics.Implications of the results are then discussed in the perspective offuture research on tree zonation, local diversity pattern and communitystructuring in tropical rainforests. [ABSTRACT FROM AUTHOR]