Rainfall interception of three trees in Oakland, California

A rainfall interception study was conducted in Oakland, California to determine the partitioning of rainfall and the chemical composition of precipitation, throughfall, and stemflow. Rainfall interception measurements were conducted on a gingko (Ginkgo biloba) (13.5 m tall deciduous tree), sweet gum (Liquidambar styraciflua) (8.8 m tall deciduous), and lemon tree (Citrus limon) (2.9 m tall broadleaf evergreen). The lemon, ginkgo, and sweet gum intercepted 27.0%, 25.2% and 14.3% of gross precipitation, respectively. The lemon tree was most effective because it retained its foliage year-round, storing more winter rainfall than the leafless ginkgo and sweet gum trees. Stemflow was more important for the leafless sweet gum. Because of its excurrent growth habit and smooth bark, 4.1% of annual rainfall flowed to the ground as stemflow, compared to less than 2.1% for the lemon and 1.0% for the ginkgo. Water samples were collected from throughfall, stemflow, and a nearby control site to measure concentrations of nutrients and heavy metals. Compared to the control, samples from under trees had higher concentrations of nutrients and metals (e.g., N, P, K, Zn and Cr), indicating that atmospheric deposition to tree crowns was a major source of pollutants. Nutrient and metal concentrations were highest in gingko tree’s throughfall. Its rough stem surfaces and dense branching pattern appeared to trap more pollutions than the other two trees.