Are floristic and edaphic patterns in Amazonian rain forests congruent for trees, pteridophytes and Melastomataceae?

Abstract

Studies in western Amazonian forests have found that similarities in soil cation concentration and texture explain floristic similarities between sites, when these are measured using trees, pteridophytes or Melastomataceae. However, it is not known to what extent the three plant groups react to the same soil characteristics, because tree studies have almost always been conducted in different areas than studies on the understorey plant groups. We made inventories in 23 sites representing non-inundated rain forests on clayey to loamy soil in three regions of western Amazonia. Significant Mantel correlations between the floristic patterns of trees and pteridophytes were found in all three regions when floristic differences were measured with species presence–absence data. When species abundance data were used, and when the floristic patterns of trees and Melastomataceae were compared, significant correlations were found in one or two regions. Mantel correlations between plant groups were highest in the two regions where the observed variation in soil characteristics was largest. In all regions, the same soil variables emerged with significant Mantel correlations with trees, pteridophytes and Melastomataceae. Soil calcium and magnesium were most frequently retained in the models of multiple regression on distance matrices. On average, soil differences explained 50% of the variation in floristic differences (range = 14–84%), and geographical distances explained 16% (range = 0–64%). Our results demonstrate that beta diversities of the three plant groups are highly correlated, and that much of this congruence is explained by similar reactions to soil variation. These results support the idea that pteridophytes, and to a lesser degree Melastomataceae, can be used as indicators of general floristic and edaphic patterns in Amazonian rain forests. Since understorey plants are much quicker to inventory than trees, this would make it possible to recognize and map floristic patterns over huge areas of lowland Amazonia within a reasonable time.

Multi-scale comparisons of tree composition in Amazonian terra firme forests

“…4). Such high beta diversity of the north-western Amazonia region has been noted previously (Tuomisto et al, 2003a;Ruokolainen et al, 2007). Conversely, our results also supported the observation that within Amazonia, some species remained dominant at large scales and therefore distant forests can be floristically rather similar.…”

“…Partial Mantel tests were used to test the relative influence of geographical distance and environmental factors, such as climate (dry season length -DSL) and soil fertility, as determinants of the floristic dissimilarity at continental and regional scales (Tuomisto et al, 2003a;Ruokolainen et al, 2007). The partial Mantel test involves computing the Pearson correlation coefficient or standardized Mantel statistic (r) as a measure of the strength of relationship between two distance matrices, while controlling for correlations with a third distance matrix.…”

“…This might be particularly important for groups of trees, such as some genera of Melastomataceae, which are aluminium accumulators (Jansens et al, 2002). For example, Tuomisto et al (2003a) and Ruokolainen et al (2007) using full inventories of Melastomataceae found that Ca and Mg explained part of the floristic patterns in terra firme forests in Amazonia while aluminium concentrations correlated with species diversity and richness (Tuomisto and Ruokolainen, 2005). Further studies of soil properties, such as phosphorus fractionation, are required in order to understand more fully the role of soils in determining floristic patterns.…”

“…However, at a regional scale within western Amazonia, floristic patterns have been related to dispersal limitation due to geographical distance, the capacity of a few groups of species to dominate large areas ("oligarchies"), large geological units, as well as fine-scale soil heterogeneity (e.g. Pitman et al, 2001;Phillips et al, 2003;Tuomisto et al, 2003a;Vormisto et al, 2004;Fine et al, 2005;Macía and Svenning, 2005;Montufar and Pintaud, 2006;Ruokolainen et al, 2007;Pitman et al, 2008;Duque et al, 2009). Different factors may well be important at different scales but the relative importance of geographical distance and environmental conditions, at both regional and continental scales, has not been studied in Amazonia.…”

Geochemical Signature of Amazon Tropical Rainforest Soils

“…Within the Amazon rainforest, several phytoecological units occur but are relatively poorly defined (Kricher, 1999). Amazon speciation, with large floristic diversity and areas of endemism, may be a consequence of the variety and distribution of soils (Sombroek, 2000;Ruokolainen et al, 2007;ter Steege, 2010;Guimarães et al, 2013), climatic variables (Clarke and Gaston, 2006), geographical barriers (Hunter Jr, 1999), and periodical disturbances that reduce dominance by species and induce competition (Collins et al, 1998). But in Brazil, these forests are home to 897 thousand native (indigenous) people who sustain themselves through subsistence agriculture, hunting, and fishing, and they are directly affected by contamination (IBGE, 2013).…”