Importance of soils, topography and geographic distance in structuring central Amazonian tree communities

Abstract

Question: What is the relative contribution of geographic distance, soil and topographic variables in determining the community floristic patterns and individual tree species abundances in the nutrient-poor soils of central Amazonia? Location: Central Amazonia near Manaus, Brazil. Methods: Our analysis was based on data for 1105 tree species (> 10 cm dbh) within 40 1-ha plots over a ca. 1000-km 2 area. Slope and 26 soil-surface parameters were measured for each plot. A main soil-fertility gradient (encompassing soil texture, cation content, nitrogen and carbon) and five other uncorrelated soil and topographic variables were used as potential predictors of plant-community composition. Mantel tests and multiple regressions on distance matrices were used to detect relationships at the community level, and ordinary least square (OLS) and conditional autoregressive (CAR) models were used to detect relationships for individual species abundances. Results: Floristic similarity declined rapidly with distance over small spatial scales (0-5 km), but remained constant (ca. 44%) over distances of 5 to 30 km, which indicates lower beta diversity than in western Amazonian forests. Distance explained 1/3 to 1/2 more variance in floristics measures than environmental variables. Community composition was most strongly related to the main soil-fertility gradient and C:N ratio. The main fertility gradient and pH had the greatest impact of species abundances. About 30% of individual tree species were significantly related to one or more soil/topographic parameters. Conclusions: Geographic distance and the main fertility gradient are the best predictors of community floristic composition, but other soil variables, particularly C:N ratio, pH, and slope, have strong relationships with a significant portion of the tree community.

The importance of crown dimensions to improve tropical tree biomass estimates

“…It has recently been shown that maximum height and H-D relationships are lower in South America than in Asia and Africa (Feldpausch et al 2011, Banin et al 2012, and within Amazonia, trees in the south are shorter than those in the northeast (Nogueira et al 2008b, Feldpausch et al 2011. We propose that this is likely to be a result from the tradeoff between vertical height growth and horizontal crown growth to maximize light capture (King 1996, Aiba and Kohyama 1997, Sterck and Bongers 1998, Bohlman et al 2008. This, in turn, suggests that models with only D and q may be more universal than models with D, q, and H. Indeed, many studies across the tropics have found that trees with greater adult stature and more slender stem allometry are also associated with narrower crowns (Poorter et al 2003, Bohlman and O'Brien 2006, King et al 2006, Aiba and Nakashizuka 2009, Iida et al 2012).…”

More than environmental control at local scales: do spatial processes play an important role in floristic variation in subtropical forests?

“…Its eff ects may be related to edaphic factors, light and water availability, and topographic characteristics (Jones et al 2011;Penã-Claros et al 2012;Baldeck et al 2013;Eisenlohr et al 2013;Oliveira-Filho et al 2013;Sanchez et al 2013;Th uiller 2013). Topography and physicochemical soil properties have been recognized as crucial drivers of vegetation mainly at local scales (e.g., O'Brien et al 2000;Bohlman et al 2008;Machado et al 2008;Souza et al 2012;Toledo et al 2012;Mélo et al 2013). Topography, for example, plays a fundamental role in the description of variations in the composition of vegetation, mainly because a variation in topography may cause alterations in the physical and chemical properties of soils (John et al 2007;Baldeck et al 2013;Mélo et al 2013).…”

Patterns of Plant Species Richness Within Families and Genera in Lowland Neotropical Forests: Are Similarities Related to Ecological Factors or to Chance?

“…However, stochastic processes seem to play a minor but significant role, given that the most species rich genera were similar between close-by areas, as predicted by neutral models. Our findings and an accumulating body of evidence show that forest composition does change along environmental gradients (e.g., Bohlman et al, 2008;Coronado et al, 2009;Engelbrecht et al, 2007;Pitman et al, 2008: Tuomisto, 2006, in spite of the occurrence of widely distributed species along Neotropical forests (Bohlman et al, 2008;Condit et al, 2002). This emphasizes the relevance of protecting in areas of high human preference, because they are usually located in particular ecological settings and floristic composition.…”