Ecological Drought in Riparian Ecosystems

Science Center Objects

Drought is killing riparian trees along many rivers in the western United States. The cause can be increasing temperature or decreasing precipitation, flow or water-table elevation. At multiple locations we are relating water availability to physiological measurements of tree survival and water stress, such as ring width, carbon stable isotope ratio and branch hydraulic conductivity. These relations will allow us to determine the minimum amount of water necessary to keep trees alive, and to predict how changes in flow, groundwater level, precipitation or temperature would affect survival.  

Stable isotopes of carbon in cottonwood tree rings provide a record of past drought stress
Stable isotopes of carbon in cottonwood tree rings provide a record of past drought stress. This figure shows the strong negative correlation between annual September-August precipitation and the 13C/12C ratio of cottonwood rings averaged across seven trees from the flood plain of the Little Missouri River in Theodore Roosevelt National Park, ND (r = -0.60). Public domain.
A Common Garden at the Colorado State Nursery in Fort Collins, Colorado, established in 2005 to study evolution of phenology
A Common Garden at the Colorado State Nursery in Fort Collins, Colorado, established in 2005 to study evolution of phenology of riparian cottonwood and saltcedar. Plants were collected along a longitudinal gradient from Texas to Montana. Phenology is the seasonal timing of life history events including leaf opening, flowering, seed release, bud formation and leaf senescence. Monitoring of about 280 cottonwoods continues at this research site (Friedman et al. 2008, 2011). Public domain.
Drought stressed Populus euphratica along the Tarim River, in the Taklamakan Desert, Xinjiang, China.
Drought stressed Populus euphratica along the Tarim River, in the Taklamakan Desert, Xinjiang, China. As a result of flow diversion, surface water no longer flows in this channel. Photo by Jonathan Friedman. Public domain.
Populus euphratica leaf bud. Photo by Jacqueline Robertson, contractor to USGS.
Populus euphratica leaf bud. Photo by Jacqueline Robertson, contractor to USGS. Public domain.

Mean of the Top Ten Percent of NDVI Values in the Yuma Proving Ground during Monsoon Season, 1986-2011

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