BOARD01713

• Board Meeting Date: 7/28/2003
• Description: CF Section - Tamarisk Control and Eradication Update
• Board Meetings - Doc Type: Memo

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Impact of Tamarisk Infestation on the
Water Resources of Colorado
May 30, 2003

Executive Summary

This document is prepared for the Colorado Department of Natural Resources' Water
Conservation Board to provide a basic understanding of the tamarisk problem in Colorado and
specifically its impact on the state's water resources. Funding for this work was provided by the
Conservation Board to the Tamarisk Coalition to prepare this report.

Tamarisk (Tamarix spp., also known as saltcedar) is a tenacious plant that has a deep root system
(up to 100 feet) and leaves a salt residue in the soil. These characteristics enable tamarisk to
quickly replace native riparian vegetation, such as cottonwoods and willows, resulting in thickets
that:
~ Increase soil salinity, rendering the soil unsuitable for other plants.
~ Have less value as wildlife habitat than native vegetation.
~ Widen floodplains by clogging stream channels.
~ Impact endangered fish by changing stream morphology.
~ Increase fire hazard and intensity.
~ Diminish human enjoyment of and interaction with the river environment.

While each of trese points is important to one or more constituencies, the single most critical
problem with tamarisk is that it uses more water than the native riparian vegetation that it
replaces; such as cottonwoods and willows. As tamarisk moves into adjacent upland habitats, it
consumes even more water as it replaces the native grass/sage/rabbit brush plant communities
which are low water consumers. This nOlrbeneficial user of the West's limited water resources
dries up springs, wetlands, and riparian areas by lowering water tables. The term "nOlrbeneficial
water use" is defined as the difference in water consumption (evapotranspiration) between
tamarisk and the native plants it has replaced.

This report is intended to provide some fundamental answers on Colorado's tamarisk problem
that may be important for water managers within the state to understand; i.e., 1) How many acres
of tamarisk exist in Colorado? 2) How much water is being used by tamarisk versus native plant
species? and 3) What is the cost of tamarisk control and reve~tation? Findings from previous
and new research, and from interviews and observations are:

1) The estimated tamarisk infestation in Colorado is 42,000 acres and 15,000 acres for
Russian-olive or a total of 57,000 acres. Russian-olive is included with tamarisk
because it is the other non-native phreatophyte that the Department of Agriculture has
identified as a problem in Colorado. Infestations occur on every major river drainage in
the state with the exception of the North Platte.

2) Using annual rates for new encroachment ranging from 1 to 2.5 percent per year,
infestations are predicted to increase to between 90,000 and 200,000 acres over the next
50 years if no active control program is put into place.

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