The environmental triangle of the Cerrado Domain: Ecological factors driving shifts in tree species composition between forests and savannas

Abstract

1. The Cerrado Domain of central Brazil houses the largest extent of savanna in the Neotropics, but despite its simple characterization as a giant savanna, it contains considerable vegetation heterogeneity that is poorly understood. 2. We aimed to determine how vegetation types in the Cerrado diverge in their tree species composition and what role ecological factors play in driving compositional patterns.3. We used a dataset of 1,165 tree species inventories spread across the Cerrado Domain, which come from six vegetation types that have a substantial arboreal component: woody savannas, dystrophic cerradão, mesotrophic cerradão, seasonally dry tropical forests, semideciduous forests and evergreen forests. We found three extremes in terms of tree species composition, with clear underlying ecological drivers, which leads us to propose a ternary model, the Cerrado Vegetation Triangle, to characterize woody vegetation in the Cerrado. At one extreme, we found that semideciduous and evergreen forests are indistinguishable floristically and are found in areas with high water availability. At another extreme lie seasonally dry tropical forests which are found on more fertile soils. At the third extreme, we found that all types of savanna, and dystrophic cerradão, are highly similar in tree species composition and are commonly found in areas of poor soils and high flammability. Mesotrophic cerradão is transitional in tree species composition between savannas and seasonally dry tropical forest. The lack of variation in tree species composition attributed to climatic variablesindicates that within homogeneous macroclimatic zones, many types of forest and savanna co-exist due to complex mosaics of local substrate heterogeneity and fire history. |

Drivers of floristic variation in biogeographic transitions: insights from the ecotone between the largest biogeographic domains of South America

“…The differences in floristic composition between savanna and forest are widely reported (Borchet 1988;Rocha et al 2009;Staver et al 2011;Davidson et al 2012;Hoffmann et al 2012;Dantas et al 2013;Oliveira et al 2014;Bueno et al 2018;Dexter et al 2018). We here confirmed this distinction, which is in accordance with our first hypothesis.…”

“…Regardless of the scale, transition zones usually cover vulnerable ecosystems that are relevant to the organisms flow (Yarrow & Marín 2007), with high biodiversity and presence of rare species (Smith et al 2001;Araújo 2002). Transitions between forests and savannas, for example, show a high variety of vegetation types, which have different characteristics, floristic composition and ecosystem functions (Bueno et al 2018;Dexter et al 2018). It is precisely in such transitions that changes in the species distribution range have been increasingly observed, being associated not only to historical and isolation factors, but also to environmental heterogeneity as global changes intensify (Poloczanska et al 2013;Neves et al 2015).…”

“…For the Amazon-Cerrado transition, evidences show a significant correlation between precipitation patterns and their forest cover (Debortoli et al 2016) and the influence of different soil attributes on vegetation structure, including species diversity (Rodrigues et al 2016). In stable and alternative states of climate, soil and natural fire, this transition undergoes a progressive replacement of its savanna vegetation by forest formations (Maracahipes-Santos et al 2018), but the existence of various types of substrates and the greater presence of fire caused by anthropogenic processes tends to promote changes in the vegetation because their effects cause a decrease in density, basal area and, consequently, in biomass (Marimon et al 2006;Bueno et al 2018;Maracahipes-Santos et al 2018). Thus, these three components (climate, soil and fire) seem to be important drivers of vegetation changes in the Cerrado-Amazon transition.…”

Inserting Tropical Dry Forests Into the Discussion on Biome Transitions in the Tropics

“…Cerradão shares some tree species with tropical dry forest and comparatively few with semideciduous and evergreen moist forests (Bueno et al, 2018), even though the latter are present near savanna vegetation along river courses and lake margins that have year-round water availability (Ribeiro and Walter, 1998). Tree species from semideciduous and evergreen forests may be less likely to immigrate into cerradão than typical dry forest tree species because they are not adapted to seasonal drought.…”

Improvement in light utilization and shoot growth in Hymenaea stigonocarpa under high CO 2 concentration attenuates simulated leaf herbivory effects

“…The higher allocation of biomass directed to aerial structures might be beneficial for the reestablishment of the species after herbivory events (Bond & Midgley 2003), or even fire, environmental filters considerably common in the Cerrado (Bueno et al 2018). However, recovery after the disturbance varies according to the intensity of the damage, since the growth of plants is positively related to the remaining LA.…”