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Quantification of stemflow in three isolated shrub species in an urban environment
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Quantification of stemflow in three isolated shrub species in an urban environment

Emma Rakestraw
Master of Science (M.S.), Drexel University
Apr 2016
DOI:
https://doi.org/10.17918/etd-6907
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Abstract

Urban ecology (Sociology)--Pennsylvania--Philadelphia Forestry, Urban--Rain and rainfall--Pennsylvania--Philadelphia Environmental Engineering
As precipitation falls on vegetated areas, it is partitioned into throughfall, stemflow and vapor. Stemflow has often been neglected in hydraulic 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 individual branches 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 attachment angle and stem circumference on the percent stemflow expected was analyzed. In addition to species characteristics, rain depth, rain intensity, wind speed, gust speed, date of storm, direction of collar, and wind direction were considered. Of the six measured individuals it was found that stemflow averaged 7.6 %, with values ranging from 0 to 58 percent for individual branches across all storms. Species specific averages were found to be 11.4 %, 7.0 %, and 4.4 % for P. laurocerasus, H. quercifolia, and I. virginica respectively. These results show that there is significant variation in stemflow percent by species. It was also determined that between 55 and 79 percent of variation in stemflow can be defined by the above characteristics. To make prediction models more accurate, more variables should be examined. By understanding how the quantity of stemflow is affected by both meteorological and species characteristics, the partitioning of rainfall can be more accurately calculated.

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