Tamarisk and invasive plants
Overview
Invasive species are those introduced to new geographic areas by human activity (i.e., non-native) and have deleterious impacts on ecosystems and society. Invasive plants typically outcompete native plants, potentially creating monocultures, decreasing biodiversity, and changing disturbance regimes such as fire. Because of their harm to native species and ecosystem services, land managers often undertake extensive control efforts. Control strategies can include chemical (herbicides), physical (mowing/removal), and biological (e.g., defoliating beetles) approaches. If invasive plants can be removed, native habitat and its original functions may be restored.
As elsewhere in the West, many invasive plant species have been introduced in the Colorado River Basin, both intentionally and accidentally, with impacts on protected species, ecosystem services, environmental health, and water availability. Like other parts of the West, the spread of invasive plants in the Basin has a been facilitated by human alterations of natural disturbance regimes (e.g., flooding, wildfires) as well as by human-caused disturbances of plants and soils (e.g., grazing, road construction).
Perhaps the most infamous invasive plant present in the Colorado River Basin is the tamarisk (Tamarix spp.), also known as saltcedar. The tamarisk is a shrub-like tree intentionally introduced to the U.S. in the 19th century for erosion control on riverbanks and railroads. Following its introduction, tamarisk spread rapidly along river corridors of the Southwest, growing in dense, monotypic stands (Figure 1). Tamarisk has replaced stands of native species such as willow along thousands of miles of stream and river corridor in the Upper and Lower Basins, altering soil chemistry, displacing native plant communities, impairing critical wildlife habitat, and–possibly–consuming more water than the native species it has replaced, though this widespread notion has been challenged.
Due to the difficulties in traditional eradication methods such as herbicides, controlled burns, and physical removal, the saltcedar leaf beetle (Diorhabda elongata) was introduced to southwestern waterways as a biological control agent. The introduction of the beetle has been largely successful in reducing the abundance of tamarisk; however, the use of the beetle, itself non-native, remains contentious. While tamarisk has been treated as a nuisance in much of the Colorado River basin, it has also provided habitat for the endangered Southwestern Willow Flycatcher (Figure 1).
Russian olive (Elaeagnus angustifolia) is a similar invasive shrubby tree that crowds out native plant and tree species and degrades the habitat for many bird and mammal species. Another widespread riparian invasive, limited to the Lower Basin, is giant reed (Arundo donax; aka giant cane), a bamboo-like grass up to 20 feet tall.
In upland areas of the Colorado River basin, especially in grasslands and shrublands that have historically had or presently have cattle or sheep grazing, a plethora of invasive plants now dominate or otherwise impact millions of acres of land, including cheatgrass (Bromus tectorum), buffelgrass (Pennisetum ciliare), Canada thistle (Cirsium arvense), musk thistle (Carduus natans), and Russian knapweed (Rhaponticum repens). Cheatgrass and buffelgrass are both notorious for facilitating fire ignition, spread, and intensity in habitats that previously had much lower levels of fire, threatening many native plant and animal species.
Russian thistle (Salsola tragus), also known as tumbleweed, is a common invasive and early colonizer of disturbed landscapes. It grows in riparian zones in the years after a disturbance and in dry upland locations associated with disturbance. Awned barnyard grass (Echinochloa crus-galli) is a 1.5 m tall invasive riparian grass from southeast Asia that can have considerable impacts to crops and can remove large amounts of nitrogen from soils.
Relevance
Variation in snowfall and the resulting size of the snowpack from year to year is the primary influence on the magnitude of seasonal (spring-summer), annual, and peak streamflows. Accordingly, monitoring the evolution of the basin's snowpack over the course of the winter and spring is critical to forecasting streamflow and managing water supply. Snow monitoring is also vital to other river-based interests, such as fisheries management and guided rafting.
Data and tools
Note: Snowpack Monitoring in the Rocky Mountain West: A User Guide provides more detailed descriptions of the datasets and tools listed below, and guidance on using them.
SNOTEL and other in-situ snow data
NRCS Interactive Map
This very versatile tool provides a clear spatial overview of snowpack (SNOTEL) and other hydroclimate conditions across the western U.S., while allowing users to easily drill down into site-level data. Displays both near-real-time data (previous day) and historical data.
NRCS State Snow Survey Snow Products
The NRCS state snow survey sites provide many additional options--varying by state-- for viewing current and historical SNOTEL and snow course data, including monthly summary reports (Basin Outlook Reports).
CBRFC Snow Groups
Provides current year's time-series plots of SNOTEL SWE averaged across multiple SNOTEL sites (“snow groups”) selected to represent a particular catchment or area; ~300 options for catchments within the Colorado River Basin and eastern Great Basin.
CoCoRaHS Interactive Map
Provides daily new snow depth and SWE, and snow depth and SWE on the ground, from the hundreds of volunteer CoCoRaHS observers in the basin. Select Map Options > What to map these snow variables.
Gridded snow products based on in-situ data
NOAA NOHRSC - SNODAS Interactive Map
Provides access to SNODAS daily gridded SWE and other snow variables; the SNODAS model builds and maintains a snowpack based on weather data and also assimilates SNOTEL data.
SnowView – Snow-Water Artificial Neural Network modeling system (SWANN)
This tool, developed at the U. of Arizona, shows a daily gridded snow dataset (SWANN) that uses snow models, assimilated SNOTEL data, and machine-learning methods. Users can compare SWANN with SNODAS for a catchment of interest.
CBRFC Modeled Snowpack – Interactive Conditions Map
Interactive map that provides daily-updated modeled SWE for ~500 catchment-elevation zones in the Colorado River Basin and eastern Great Basin. These modeled SWE data are used as key inputs for CBRFC's seasonal streamflow forecasts.
Gridded snow products based on remotely-sensed data
ASO (Airborne Snow Observatories, Inc.) - Basin Map
ASO uses airborne lidar to measure snow depths across a basin on demand; these depth measurements are combined with snow-density modeling to estimate SWE with high accuracy at 50-m spatial resolution. Free registration required to view the data for all ASO-flown basins.
- For more information about ASO activities in Colorado, see the Colorado Airborne Snowpack Monitoring Program (CASM) webpage
Other snowpack information
Colorado Dust-on-Snow (CODOS) reports
The CODOS program at the Center for Snow and Avalanche Studies (CSAS) tracks the deposition and emergence of dust layers in the snowpack, and snowpack temperature and other metrics, at 11 mountain pass locations throughout Colorado.
Additional resources
State of the Science Report
Chapter 2 of the State of the Science report, Section 2.5, provides an overview of the basin's snowmelt-dominated hydrology and key snowpack processes and patterns.
Chapter 5 of the State of the Science report, Section 5.1, describes the different methods for snowpack monitoring in much greater detail, along with links to several snow-monitoring tools.
Snowpack Monitoring in the Rocky Mountain West: A User Guide
This user guide expands on Section 5.1 of the State of the Science report with guidance on selecting appropriate snow-monitoring data and tools, and guidance on accessing and using the different online tools.