Stemflow variability across tree stem and canopy traits in the Brazilian Cerrado

Abstract

The Cerrado savanna of Brazil is considered the most biodiverse savanna in the world and its vegetation acts as an interface between rainfall and recharge processes for the largest aquifer system (Guarani) in South America. Understanding how major Cerrado tree species affect the amount and patterns of rainfall at the surface, therefore merits scientific attention. Some rainfall that contacts the Cerrado canopy will be drained to a concentrated area around the stem base as ‘stemflow.’ Hypothetically, this spatially concentrated hydrologic flux may contribute nontrivially to recharge. Here, we examine stemflow variability over 13 months for 151 trees, representing 36 species common to the region, with a large range in stem and canopy structures. Bark texture, stem diameter at breast height (D) and the canopy height-to-width ratio (H:W) were measured for all trees, then individuals were sorted into three classes: smooth, scaled and furrowed bark texture; < 10, 10–20 and > 20 cm D; and < 1, 1,2 and > 2 canopy H:W. These data were used to investigate how tree morphological traits influence stemflow in the Cerrado. Stemflow over the study period represented 2.5% of rainfall, and the contribution of each morphological class to the region's scaled total stemflow yield was calculated. Although median stemflow volumes per storm were significantly different between bark textures (smooth > scaled > furrowed); the interrelated effects of canopy structure (H:W) and tree size (DBH) resulted in a relatively well-balanced representation of all bark classes to the Cerrado's total stemflow yield (41% from smooth-barked trees, 30% scaled-bark trees, and 29% furrowed-bark trees), regardless of the density of individuals belonging to each class analyzed. Large trees (D>20) with low canopy H:W<1 and scaled bark produced the lowest median stemflow fractions. The highest contribution to stand-scale stemflow yield in this Cerrado study was linked to the combination of stem and canopy traits in three ways: (1) trees with smooth bark dominated by D<10 and H:W1-2; (2) trees with D10–20 dominated by smooth bark and H:W1-2 ratio, and (3) trees with H:W1-2, dominated by smooth/furrowed bark trees and D<10. These findings highlight the importance of trait-based approaches in studying how tree stem (bark), size (DBH), and canopy (H:W) structural traits interact to affect stemflow generation, while filling a knowledge gap regarding the ecohydrology of the Brazilian Cerrado.