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Foliage and Stem Drag: Comparison Between Four Riparian Species

Author(s): Kaisa Vastila; Juha Jarvela

Linked Author(s): Kaisa Västilä, Juha Järvelä

Keywords: No Keywords

Abstract: This paper investigates the flow resistance of foliated trees by partitioning the total drag into two components: foliage drag and stem drag. The drag forces of four foliated and defoliated Common Osier (Salix viminalis), hybrid Crack Willow (Salix x rubens), Common Alder (Alnus glutinosa) and Silver Birch (Betula pendula) were directly measured. The foliage drag was determined by subtracting the stem drag from the total drag. The relationship between the drag and readily measurable plant properties was analyzed for each species. The stems were characterized using four properties: dry mass, wet mass, frontal bent stem area, and volume. The stem drag per each of these properties was similar for all four species. Therefore, the stem drag of leafless twigs of these species can be estimated using the same relationships. The foliage was characterized using three properties: dry mass, wet mass, and one-sided leaf area. For Alnus glutinosa, Betula pendula and Salix x rubens, the foliage drag per any of the three properties was1. 5-3 times higher compared to Salix viminalis. The most notable differences between the species were observed in the foliage drag per leaf dry mass. The foliage drag per leaf area was similar for Alnus glutinosa, Betula pendula and Salix x rubens, indicating that the same relationships can be applied for predicting the foliage drag of these species. The findings implied that the between-species variability in the flow resistance of foliated twigs resulted mostly from the differences in the leaf properties rather than the stem properties.


Year: 2012

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