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Title: Native Trees and Salt Cedar: Quantifying Transpiration at Intermittent and Perennial Streamflows on the San Pedro River 1933

Author
item McGuire, Roberta
item GLENN, E. - UNIVERSITY OF ARIZONA
item Scott, Russell - Russ
item Moran, Mary

Submitted to: American Geophysical Union
Publication Type: Proceedings
Publication Acceptance Date: 10/19/2007
Publication Date: 12/11/2007
Citation: Mcguire, R.R., Glenn, E.P., Scott, R.L., Moran, M.S. 2007. Native Trees and Salt Cedar: Quantifying Transpiration at Intermittent and Perennial Streamflows on the San Pedro River. American Geophysical Union Meeting, Dec. 10-14, San Francisco, CA. {abstract}.

Interpretive Summary: Native cottonwood-willow forests that historically dominated south-western riparian areas are being replaced by salt cedar (Tamarix ramosissima) on the majority of regulated western rivers. Some studies of salt cedar have indicated its water use is considerably greater than native trees and depletes alluvial aquifers of groundwater; however, other studies have shown low to moderate water use by salt cedar. Results have varied on temporal and spatial scales making it difficult to draw firm conclusions. We compared whole plant transpiration by native riparian cottonwood (Populus fremontii) trees and salt cedar in co-occurring communities at the upper and lower San Pedro River in Arizona during 2006 and 2007, respectively. Water use by both species was monitored and quantified using the heat balance sap flow technique at intermittent and perennial reaches during the pre-monsoon season, a period of high atmospheric water demand. Our 2006 measurements in a riparian transition zone at an intermittent reach of the San Pedro River appeared to differ with earlier studies that salt cedar has higher transpiration rates, as cottonwoods and salt cedar demonstrated similar, low transpiration rates. However transpiration results from a 2007 study on these same species at a perennial reach of the San Pedro River indicate significantly higher transpiration by salt cedar and moderate increases for cottonwoods compared to the intermittent site.

Technical Abstract: Native cottonwood-willow forests that historically dominated south-western riparian areas are being replaced by salt cedar (Tamarix ramosissima) on the majority of regulated western rivers. Some studies of salt cedar have indicated its water use is considerably greater than native trees and depletes alluvial aquifers of groundwater; however, other studies have shown low to moderate water use by salt cedar. Results have varied on temporal and spatial scales making it difficult to draw firm conclusions. We compared whole plant transpiration by native riparian cottonwood (Populus fremontii) trees and salt cedar in co-occurring communities at the upper and lower San Pedro River in Arizona during 2006 and 2007, respectively. Water use by both species was monitored and quantified using the heat balance sap flow technique at intermittent and perennial reaches during the pre-monsoon season, a period of high atmospheric water demand. Our 2006 measurements in a riparian transition zone at an intermittent reach of the San Pedro River appeared to differ with earlier studies that salt cedar has higher transpiration rates, as cottonwoods and salt cedar demonstrated similar, low transpiration rates. However transpiration results from a 2007 study on these same species at a perennial reach of the San Pedro River indicate significantly higher transpiration by salt cedar and moderate increases for cottonwoods compared to the intermittent site.