Repelling the Invaders

Many of us who’ve been involved with restoration projects have had to deal at some point with invasive plant species. Often introduced to their new environment with the best of intentions, non-native plants—and non-native animals, for that matter—can often take over at the expense of indigenous species. Such was the case in Arizona with the salt cedar, also known as the tamarisk, a shrub native to central Asia. It was brought to the western US in the 1800s and used to create windbreaks and to control erosion. It quickly spread, however, and crowded out native plants like cottonwood and willow.

Many of us who’ve been involved with restoration projects have had to deal at some point with invasive plant species. Often introduced to their new environment with the best of intentions, non-native plants—and non-native animals, for that matter—can often take over at the expense of indigenous species. Such was the case in Arizona with the salt cedar, also known as the tamarisk, a shrub native to central Asia. It was brought to the western US in the 1800s and used to create windbreaks and to control erosion. It quickly spread, however, and crowded out native plants like cottonwood and willow. [text_ad] As detailed on the Arizona Municipal Water Users Association blog a few months ago, in some parts of Arizona salt cedar now accounts for more than half the vegetation. The water-hungry shrub—which can absorb more than 200 gallons a day—grows along rivers and in wetland areas, and in some places the growth within the riverbed is so thick that during heavy storms the water, with nowhere else to go, overtops the banks and floods surrounding property. The plant also burns readily during fire season—a dangerous situation when the salt cedar groves are near populated areas. A few years ago in Colorado, an attempt was made to eradicate the salt cedar by releasing salt cedar beetles, native to Kazakhstan, to destroy the trees without using herbicides. It worked almost too well, killing the shrubs not only in the intended areas but also in areas where endangered birds were nesting in it. Arizona is trying two different methods to reduce the amount of salt cedar. One is to burn it and replace it with native plants. The other is to clear the ground, leave it fallow for a year, and then bring in native species along with irrigation to help the plants get started. The latter method is more effective but also more expensive, and the Flood Control District of Maricopa County is continuing to explore different options. Have you faced a similar situation in your area, with invasive weeds or other plants getting out of control, especially in riparian areas? Have they affected plans for riparian stormwater buffers in areas of new development? And what have you found is the best way to deal with them?