Functional Biogeography and Ecological Strategies of Trees Across the Amazon–Cerrado Transition

Question

We asked how community functional traits differ among vegetation types at the transition zone between the Amazon forest and Cerrado savanna biogeographic domains, and which environmental variables best predict these changes in functional structure.

Location

The large transition zone between the Amazon and Cerrado biogeographic domains.

Methods

We field-collected and analyzed an extensive new database of 182 tree species from six vegetation types, resulting in 55,895 records of functional traits. We selected 15 traits that affect different aspects of ecosystem processes and ecological strategies of trees. Then we compared the distribution of functional traits among vegetation types and assessed their association with edaphic and macroclimatic variables.

Results

We recorded a functional continuum between the extremes of Cerrado (Typical Cerrado) and the Amazon (Open Ombrophilous Forest), with most traits forming a gradient along the vegetation types. Our data also indicate that tree-dominated Cerrado formations (Cerradão) are functionally intermediate between savannas and forests, reinforcing the importance of accounting for the full floristic and structural variation of neighboring biogeographic domains. Our work revealed that CEC, soil pH, mean temperature, maximum temperature, total precipitation, and climatic water deficit are consistently related to key functional traits across the Amazon–Cerrado transition.

Conclusions

Functional traits can be used to efficiently characterize and distinguish multiple communities where South America's two largest biogeographic domains meet. We were able to delimit morpho-physiological requirements that ensure tree species' maintenance in different vegetation types and to characterize the transition zone in terms of ecosystem functioning. Woody vegetation can vary greatly in terms of ecological strategies. Hence, to understand the rules of assembly, boundaries, and full complexity of transitions, it is essential to account for functional differences.