influence of rainfall depth class and deciduous tree traits on stemflow production in an urban park

The growing recognition of trees’ value in urban environments is resulting in increased investment in “green infrastructure.” However, generalizations that deciduous canopies reduce stormwater are based largely on closed-canopy forests, highlighting the need for more detailed study of isolated urban trees. We systematically studied the effect of canopy traits on stemflow percent and funneling ratios for isolated deciduous trees in a semi-arid climate characterized by mostly small precipitation events. High stemflow production was generally associated with high branch angles (single- and multi-leader trees) small diameter-at-breast-height (single-leader trees), furrowed bark in single-leader trees for rain events ≥ 10 mm, and smooth bark in multi-leader trees for all except the lowest rain depth class. Higher numbers of leaders converging at the base were associated with high stemflow yields. Individual-tree stemflow percent and funneling ratio values were variable, even for similar rain depths, suggesting that meteorological factors play a role. Event maximum stemflow percent was 22.8 % (25.6 mm rain depth) for a columnar English oak and event maximum funneling ratio was 196.9 (5.6 mm) for a Riversii European beech. Our findings highlight the importance of infiltration capacity at the base of urban trees and of designing for the rainfall regime when integrating stormwater management with vegetation and soils in cities.