Evolution of Tree Architecture in the Brazilian Cerrado

Abstract

The tropical savanna-forest boundary is commonly characterized by an abrupt transition in vegetation structure and in tree species composition. It has been hypothesized that differences in architecture between savanna and forest trees have an important role in determining the contrasting structural differences between savanna and forest ecosystems. Because of the importance the vegetation structure in determining the ecosystem properties of these systems, I performed a comparative study of tree architecture to examine differences in plant structure of savanna and forest species. To eliminate the potential bias from phylogenetic relatedness, I used congeneric species pairs containing trees of both habitat types that occur sympatrically in savannas of the Brazilian cerrado habitat at IBGE Ecological Reserve (RECOR). I found that relative to savanna species, forest species have larger crown volumes with more apical meristems and greater height for a given stem diameter. Other traits that influence patterns of light interception also differed, with savanna species exhibiting more convoluted leaf blades and shorter petioles. There was evidence that allometry and other traits are convergent in savanna and forest tree species across lineages, providing strong support for adaptive functions of these traits. Furthermore, the larger canopies of forest species imply that they play a role in reduced light in the understory and the exclusion of grasses, which potentially facilitates further expansion of forest tree species in the absence of fire.