Riparian Ecology

Science Center Objects

Riparian ecologists at the Fort Collins Science Center study interactions among flow, channel change, and vegetation along rivers across the western United States and worldwide. Our work focuses on issues relevant to the management of water and public lands, including dam operation, climate change, invasive species, and ecological restoration. Investigations take place on a range of scales. For example, experimental studies in pots and growth chambers detect genetic, phenotypic, and species variations in response to environmental conditions, such as drought, frost, mycorrhizal inoculation, salinity, and carbon dioxide enrichment.

Erosion along the Rio Puerco during the flood of 2006 following herbicide application to control saltcedar in 2003.

Flood erosion along the Rio Puerco, NM, following control of saltcedar using herbicide applied by helicopter.  The dead shrubs on the left bank are saltcedar. Photo by Kirk Vincent.

The site-specific case studies below examine processes and patterns of exotic species invasions, impacts of dams and consequences of climate change, while regional studies examine general patterns along environmental gradients, consequences of variation in water flow, and effects of human activities across the western United States.


Erosion and Invasive Saltcedar - Principal Investigators - Jonathan Friedman and Patrick Shafroth

Formation of arroyos in the late 1800s greatly increased erosion across the southwestern United States. Since the 1930s, however, this erosion has decreased, partly because of bank stabilization by introduced saltcedar. With Isleta Pueblo Indian Nation, the Aquatic Systems Branch developed a new sediment dating method using saltcedar tree rings. We applied the method in a landmark study of arroyo filling along the Rio Puerco, New Mexico. We then showed how aerial application of herbicide to control saltcedar accidentally renewed erosion. This erosion may now be amplified by a beetle introduced for saltcedar control. 



The Little Missouri River, flood plain

The Little Missouri River, flood plain and surrounding badlands in the North Unit of Theodore Roosevelt National Park. Leafless gray trees on the flood plain are mostly cottonwood, and dark green trees are rocky mountain juniper. Cottonwood stands occur in arc-shaped bands increasing in age with distance from the channel. Photo looking downstream by Jonathan Friedman, April 22, 2012. Public domain.

Reconstructing Flow History From Riparian Tree Rings - Principal Investigator - Jonathan Friedman

Shifts in river flow regimes are a major threat to water supplies and riverine ecosystems. Understanding and predicting flow changes and their effects on vegetation are critical to effective river management. Aquatic Systems Branch scientists analyze rings of riparian trees relating tree growth and establishment to historical flow. We then use the tree rings to reconstruct the flow in past centuries. Flow reconstructions discover the frequency and magnitude of past droughts and floods—information that is essential for management of rivers and water supplies. We also use downscaled climate projections and watershed models to predict changes in flow and tree growth resulting from human-induced climate change. We have pioneered the use of cottonwood, a dominant riparian species, for tree ring analysis; this is a significant advance in arid regions where old trees of other species are otherwise scarce. Ongoing studies focus on rivers of the Upper Missouri Basin and the Tarim River in China.



The unregulated Santa Maria River in west-central Arizona.

The unregulated Santa Maria River in west-central Arizona. Photo by Patrick Shafroth, USGS. Public domain.

Streamflow-fluvial Geomorphology-riparian Vegetation Interactions - Principal Investigators - Patrick ShafrothJonathan FriedmanGregor Auble

The foundation for applying science to river and riparian restoration contexts lies in a basic understanding of the factors that drive riparian vegetation dynamics. Much of our research is focused on clarifying relationships between streamflow, fluvial geomorphology, and riparian vegetation, including various feedbacks. In some cases this work involves studying river reaches or segments that are relatively unaltered by anthropogenic activities; in many cases it involves study of river segments that have been altered by human activities, most notably river damming. Our research often includes field studies, but also experiments (e.g., in greenhouses) to help control for specific factors hypothesized to influence riparian plants. This work is often done in collaboration with scientists whose primary emphasis lies in the physical sciences (e.g., fluvial geomorphology, hydrology).


Extensive defoliation of tamarisk (orange/brown vegetation throughout mid-ground) along the Virgin River, Arizona, 2009.

Extensive defoliation of tamarisk (orange/brown vegetation throughout mid-ground) along the Virgin River, Arizona, 2009. Photo by Patrick Shafroth, USGS. Public domain.

Biological Invasions of Riparian Ecosystems - Principal Investigator - Patrick ShafrothJonathan Friedman

Beginning in the early twentieth century, non-native species of shrub, including tamarisk (also commonly known as salt cedar) and Russian-olive, were introduced to the United States for use as ornamental plants and in erosion-control plantings. By the early twentieth century, these plants had spread extensively, becoming the third and fourth most frequently occurring woody riparian plants in the American West. In the western US, the majority of riparian restoration projects involve control of these, and other, non-native species. We have researched many aspects of these plants, such as understanding environmental factors required for establishment, growth, and spread, as well as interactions with channel change, riparian water use, and wildlife. Current projects are focused on understanding vegetation recovery following biological control of tamarisk, including detailed studies on the Virgin and Colorado rivers; on the dynamics of riparian vegetation following extensive removal of Russian Olive on the Escalante River; and on understanding the distribution and abundance of Siberian Elm in the Upper Colorado, Platte, and Rio Grande basins.


Bill Williams River, Arizona, during an experimental flood in 2010. Photo by Pat Shafroth, USGS.

Bill Williams River, Arizona, during an experimental flood in 2010. Photo by Pat Shafroth, USGS. Public domain.

Large-scale streamflow experiments - Principal Investigator - Patrick Shafroth

Because the underlying cause of riparian system alteration is often attributed to the effects of dams on flow regime, managing flow releases, particularly high flows, from dams is an often-advocated approach to river and riparian restoration. Our work has focused on understanding effects of managed high flow releases (a.k.a., pulse flows, controlled floods) from dams along rivers in the lower Colorado River basin. On the Bill Williams River in western Arizona, we have had the opportunity to help design and monitor the effects of several high flow releases since the mid 1990’s. On the main stem of the Colorado River, we helped study the effects of the 2014 “pulse flow” to the Colorado River delta (Minute 319), and are working with a range of collaborators to provide input to possible future releases to the delta (Minute 32X). Finally, we are working with collaborators from USGS, USDA Forest Service, and Northern Arizona University to understand how different groups of riparian plants (“riparian response guilds”) respond to high flow experiments on the Colorado River in Grand Canyon.


The South Platte River. USGS Water Science Center image.

The South Platte River. USGS Water Science Center image. Public domain.

Science to Inform Riparian Ecosystem Restoration and ManagementPrincipal Investigators - Patrick ShafrothJonathan FriedmanGregor Auble

Throughout the world, riparian habitats have been dramatically modified from their natural condition.  Dams are often principal drivers of these changes, via their alteration of water and sediment regimes that determine key resources for riparian plants. Another common perturbation in riparian ecosystems is the spread of non-native, invasive species. Climate change can interact with these variables to drive further changes to riparian areas. Because of the array of ecological goods and services provided by riparian ecosystems, their restoration have become the focus of many land and water managers. Efforts to restore riparian habitats and other riverine ecosystems have included managing flow releases downstream of dams to more closely mimic natural flows, controlling invasive species in combination with other restoration actions, and, occasionally, dam removal.


Glines Canyon Dam on the Elwha River, during the dam removal process. Photo credit: National Park Service

Glines Canyon Dam on the Elwha River, during the dam removal process. Photo courtesy of National Park Service. Public domain.



Riparian vegetation response to dam removal - Principal Investigator - Patrick Shafroth

Dam removal is an approach to river restoration that is becoming increasingly common. In most cases, dam removal is driven by considerations other than river restoration (e.g., dam safety), but how dam removal affects aquatic and riparian systems is of great interest in many dam removals. Our work in this area has had two foci thus far: 1) studies of vegetation change associated with dam removal along the Elwha River, Washington; 2) syntheses of dam removal effects. 





Dead and dying cottonwoods along the Mojave River, California, following a decrease in the riparian water table

Dead and dying cottonwoods along the Mojave River, California, following a decrease in the riparian water table caused by downcutting in a flood. Photo by: Greg Auble, USGS. Public domain.

Ecological Drought in Riparian Ecosystems - Principal Investigators - Jonathan Friedman and Patrick Shafroth

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.