Quantification of Stemflow in Three Shrub Species in an Urban Environment

Abstract:

As precipitation falls on vegetated areas, it is partitioned into throughfall, stemflow and vapor. Stemflow has often been neglected in hydrologic budgeting of both trees and shrubs due to the small volume, and limited number of quantitative studies conducted. Studies of stemflow in shrub species are especially rare, and this study intends to decrease uncertainty of its occurrence. Six shrubs of species Prunus laurocerasus ‘Otto Luyken', Hydrangea quercifolia ‘Alice’ , and Itea virginica ‘Little Henry’ were studied in an urban environment in Philadelphia, PA. During the 2015 growing season, total incident rainfall and measured stemflow were recorded. Stemflow was collected using aluminum collars attached to four stems of each individual. Vinyl tubing transported stemflow from the collars into collection bottles that were weighed after each rain event.

Canopy areas of each collared branch were calculated. Impact of branch and leaf attachment angles, leaf area index, stem diameter, and bark properties on stemflow were analyzed. In addition to species characteristics, rain depth, rain intensity and wind speed were considered. Stemflow averages were found to be 12 %, 4 %, and 3 % for P. laurocerasus, H. quercifolia, and I. virginica respectively, with values up to 24 % in certain P. laurocerasus branches during some storms. The results show that although in some shrub species stemflow may be negligible, in others it can be high enough to be considered substantial in hydrologic budget calculations. By examining how the quantity of stemflow is affected by both meteorological and species characteristics, the partitioning of rainfall can be more accurately calculated.