Distinct Rainfall Interception Profiles among Four Common Pacific Northwest Tree Species

Forest tree canopies have a critical influence on water cycles through the interception of precipitation. Nevertheless, radial patterns of canopy interception may vary interspecifically. We analyzed canopy interception using catchments along radial transects underneath four common forest tree species (Acer macrophyllum, Alnus rubra, Pseudotsuga menziesii, and Thuja plicata) in the Pacific Northwest over two years. Near the center of the canopy in the leaf-off season, interception was 51.6%–67.2% in conifer species and only 20.1%–40.1% in broadleaf species, and interception declined to 19.9–29.9 for all species near the edge of the canopy. One deciduous species (A. rubra) showed spatially uniform interception during the leaf-off period (19.9%–20.96%), while another varied from 23.1%–40.1%. Patterns were more pronounced in the leaf-on period (under high vapor pressure deficit conditions), where conifers intercepted 36.5%–95.9% of precipitation, depending on the species and position under the canopy. Deciduous species similarly intercepted 42.1%–67.7% of rainfall, depending on species and canopy position. Total throughfall was curvilinearly related to the amount of rainfall near canopy centers for conifer trees but less so for deciduous trees. Soil moisture was predictably related to interception across and within species. These data highlight interspecific differences in radial interception patterns, with consequences for soil moisture, hydrologic processes, and ecosystem function.