Tree floristics and structure across Western Amazon flooding gradients: várzea vs. igapó floodplain forests

Because flooding gradients are common within forested ecosystems in the Amazon, I compared how flooding by white-water vs. black-water rivers affect the tree floristics and structure of the resulting várzea vs. igapó floodplain forests. I did this by sampling trees across their spatial flooding gradients in plots (microsites) starting at the river’s edge and going into each floodplain forest. I found in várzea 40 families where Fabaceae (Leguminosae), Meliaceae, Lecythidaceae and Euphorbiaceae were most frequently sampled and the spatial distribution patterns of Meliaceae, Euphorbiaceae, Fabaceae and Cecropiaceae significantly fit mathematical models (the asymmetric unimodal right-skewed model was most common) which made them also spatial gradients, and in igapó 20 families where Fabaceae and Lecythidaceae were most frequently sampled and those two families as well as Vochysiaceae significantly fit mathematical models (the asymmetric unimodal right-skewed model was again most common) which made them also spatial gradients. I also found in várzea stem density, stem mean size, basal area and species richness all increased (while Fishers’ α diversity index decreased) as plots were sampled further away from the river and family richness, species richness and Fishers’ α significantly fit mathematical models (the asymmetric unimodal left-skewed model was most common) which made them also spatial gradients, and in igapó family richness, genus richness, species richness, and mean stem size were highest in plots closest to the river while Fishers’ α was lowest in plots farthest away and stem density, mean stem size and family richness significantly fit mathematical models (there was no trend for common types of models) which made them also spatial gradients. I conclude distributions and gradients of várzea and igapó were more similar than dissimilar in familial composition and half of both of their structural parameters fitted models which, taken together, suggested dominance of the physical effects of flooding over the chemical effects of the water-type (white vs. black). In addition, familial distribution patterns were individualistic where “preferred” microsite “niches” at certain distances from the rivers may exist for some common families.