Effects of Wood Anatomy, Climate, Soil Type, and Plant Configuration Variables on Urban Tree Transpiration in the Context of Urban Runoff Reduction: A Systematic Metadata Analysis

Urban trees are increasingly deployed as nature-based infrastructure to mitigate heat and manage stormwater, yet quantitative guidance on how species traits and site context shape transpiration remains fragmented. We conducted a systematic metadata analysis of seven field studies that measured daily transpiration rate in urban settings using heat-pulse methods. The units and spatial scales reported were harmonized with the sap flow density across active sapwood (Js, g H2O/cm2/day) by converting reported stand transpiration and the outer 2 cm of sapwood sap flux using established Gaussian radial distribution functions for angiosperms and gymnosperms, which account for the non-linear decline in sap flux from the vascular cambium to the heartwood boundary. We then summarized distributions and tested group differences with Kruskal–Wallis and Dunn post hoc comparisons across wood anatomy, climate, soil texture, and planting configuration. Conifers exhibited significantly lower median Js (39.76 g/cm2/day) than angiosperms, while the ring-porous group (median Js = 92.25 g/cm2/day) and diffuse-porous groups (median Js = 96.70 g/cm2/day) had similar distributions overall. Climate-modulated responses within wood anatomy groups differed, with diffuse-porous species exhibiting the highest median Js (152.59 g/cm2/day) in semi-arid regions, ring-porous species maintaining comparatively stable median Js across climates (varying slightly between 80.72 and 99.32 g/cm2/day), and conifers reaching their highest median Js (69.90 g/cm2/day) in humid continental sites. Soil texture effects were consistent with moisture availability: sandy loam generally reduced Js relative to loam or silt loam for conifers and diffuse-porous species. Across anatomies, single trees transpired more than clustered trees or closed canopies. For example, planting as single trees increased median Js by 86% in conifers (from 33.01 to 61.37 g/cm2/day) and by 45% in diffuse-porous species (from 81.31 to 118.25 g/cm2/day). These results provide actionable ranges and contrasts to inform species selection and planting design for urban greening and runoff reduction, while highlighting data gaps for future research. Ultimately, by matching specific wood anatomies and planting configurations to local soil and climatic conditions, urban planners and ecohydrologists can strategically optimize urban forests to maximize targeted ecosystem services.