Study area and biodiversity data
Our study sites were located in the Campos Sulinos region, southern Brazil. The Campos Sulinos encompasses the northern portion of Río de la Plata grasslands (Soriano et al. 1991; Andrade et al.2018), along with grassland enclaves inside the southern tip of the Atlantic Forest (Andrade et al. 2016). The climate in the region is humid subtropical with no pronounced dry season, ranging from hot summers (Cfa type) in lowlands to temperate summers (Cfb type) in higher altitudes, according to Köppen’s classification (Alvares et al.2013).
Plant species were surveyed during the growing season, which comprises spring and summer, between 2014 and 2016 (see Menezes et al. 2022 for more details). The communities were sampled in 108 250-m long, contour transects nested in twelve 5 x 5 km grids (Figure 1). Each transect was subsampled by 10 quadrats of 1 m2, which were pooled for our analyses, thus forming a 250-m long unit we called a “plot” for the sake of simplicity. We characterized the functional community structure of the plots using leaf traits known by their representation of ecological trade-offs involved in biomass production (Lundgren et al. 2014; Engel 2017; Bruelheide et al. 2018; Testolin et al. 2021), thus they were considered effect traitssensu Lavorel & Garnier (2002). These traits were leaf area (LA – mm2), specific leaf area (SLA – mm2.mg-1), leaf dry matter content (LDMC – g.g-1), leaf nitrogen (leaf N – mg.g-1) and photosynthetic pathway (categorical, C3 or C4) which were collected from plant species sampled in situ or obtained from the TRY database (Kattgeet al. 2011) and TRY gap-filled (Schrodt et al. 2015). Missing trait values were imputed (Penone et al. 2014) using themissForest function of the package missForest (Stekhoven & Bühlmann 2012). For all plots, with these traits we calculated single trait community-weighted means (CWM), Gini-Simpson index of species diversity (for simplicity, hereafter “species diversity”) and functional redundancy (FR; difference between Gini–Simpson index of species diversity and Rao entropy) (de Bello et al. 2007). Life form, considered as a response trait (Pillar & Orlóci 1993), obtained from Ferreira et al. (2020) or collected from virtual herbaria (BFG 2022), was used to calculate Rao’s quadratic entropy (Rao 1982), which was taken as functional response diversity. We computed CWM using the function functcomp of package FD (Laliberté et al.2014), and species diversity, Rao entropy and functional redundancy using the function rao.diversity from package SYNCSA (Debastiani & Pillar 2012).