The role of edaphic factors on plant species richness and diversity along altitudinal gradients in the Brazilian semi-arid region

Abstract

Unlike well-known global patterns of plant species richness along altitudinal gradients, in the mountainous areas of the Brazilian Caatinga, species richness and diversity reach their maxima near mountain tops. The causes of this unusual pattern are not well understood, and in particular the role of edaphic factors on plant community assembly along these gradients has not been investigated. Our goal was to assess the role of edaphic factors (fertility and soil texture) on plant community composition and structure on two mountains of the Brazilian semi-arid region. In 71 plots (Bodocongó site, twenty-one 200-m2 plots, 401–680 m asl; Arara site, fifty 100-m2 plots, 487–660 m asl) we recorded 3114 individuals representing 61 plant species; in addition, at each plot we collected composite soil samples from 0–20 cm depth. Significant altitude-related changes were observed both for community structure and composition, and edaphic variables. A canonical correspondence analysis allowed the distinction of two groups of plots according to species abundances, indicating a preferential habitat distribution of species depending both on altitude and soil variables. Although soil fertility was lowest at the highest altitudes, these areas had high richness and diversity. Conversely, the more fertile foothills were characterized by the dominance of generalist pioneer species. Despite the relatively short altitudinal range that characterizes the studied mountains, this study elucidates the role of edaphic factors on the floristic composition and species richness patterns on the mountains of the Brazilian semi-arid region.

Effects of topographic factors on distribution of cacti along an elevation gradient in Brazilian Caatinga

“…With lively relief, granitic massif, soils very susceptible to erosion, with varied depth and fertility (in general, fertile) (Velloso et al 2002). Comprises an altitudinal range of 480 to 660 m a.s.l., with a heterogeneous topography and soil along this gradient (Ramos et al 2020), and in some areas with peaks reaching up to 1.000 m a.s.l. The climate of the region is tropical, dry and hot (Álvares et al 2014), with annual rainfall between 300 and 600 mm, concentrated within a two to fourmonth period, which accounts for 65% of the total annual rainfall (Souza et al 2020).…”

“…The region exhibits a mosaic of vegetation types strongly determined by environmental factors (Prado 2003;Moro et al 2016). Surrounding the mountain occurs a mosaic of natural vegetation and areas managed for agriculture and extensive livestock, with trails left by grazing domestic animals, mainly goats (Capra aegagrus), and selective cut marks in the vegetation, are commonly found at the base of mountain (Ramos et al 2020). The vegetation within the gradient is predominated by the shrubby strata with few trees, but, at the intermediate elevation to the top, with a greater rock cover and steep slopes (Diniz 2016), occurs a Caatinga arborea with higher tree density and size Rodriguésia 72: e02222018.…”

“…2021 with bromeliads in the understory, as well as species richness and the presence of some typical taxa of humid regions (e.g. Clusia paralicola G.Mariz), when compared to lower altitude vegetation (Diniz 2016; Almeida et al 2019;Ramos et al 2020).…”

“…Topographic conditions in these areas can influence the composition and structure of plant communities due to micro-environmental heterogeneity (Kouba et al 2014;Kraft et al 2015;Méndez-Toribio et al 2016;Silva & Souza 2018). For example, gravity-driven movement of nutrients from mountain top downwards has resulted in deeper and more fertile soils at the base of mountains (Santos et al 2009;Ramos et al 2020). In addition, the stock and composition of litter varies along these gradients, which can contribute to changes in patterns of species richness (Almeida et al 2020).…”

From vegetation ecology to vegetation science: current trends and perspectives

“…Some factors such as atmospheric pressure, temperature, and solar irradiance covary with elevation and can be related to other environmental variables such as precipitation, soil attributes, and geology (e.g., Ramos et al 2020), but temperature and land area emerge as the most important factors explaining changes in the biota along elevational gradients (Körner 2007, Sundqvist et al 2013. As in the case of horizontal environmental variation, new insights into the variation of vegetation structure along elevational gradients can be gained from a spatially high-resolution assessment of environmental variation, including microclimatic conditions (e.g., Salas-Morales et al 2015).…”