Tamarisk and why it has overstayed its welcome
Editors note: This is the first of a three-part series on the invasive tamarisk plant and efforts to control it in southeastern Utah. The plant has spread up the tributaries of the Colorado River, including into Emery County via the Green River over the years).
One of the reasons tamarisk was introduced in this country in the early 1800s was its ability to control erosion in arid areas and to stabilize shifting sands by taking even along washes which were usually dry. People could use it to landscape the desert.
It has a couple of features which help it thrive in harsh conditions. Deep tap roots allow it to seek out water, even when streams dry up. It can also tolerate high salinity, as it can remove salt from water and redistribute it to the surrounding soilâhence its other common name, salt cedar.
However, tamarisk is an aggressive competitor, and it doesn't limit itself to intentional landscapes. Each tamarisk flower can produce thousands of seeds, and they are dispersed by the wind.
"Tamarisk wasn't really brought (to southeastern Utah) it just started blowing in, because it's mostly a windborne seed," Wildland Scapes of Moab owner Kara Dohrenwend said. "It's moved from downstream to upstream. It's not moving from the headwaters to the mouth, it's kind of going backwards."
Dohrenwend has turned her passion for indigenous plants into a business. While she said she enjoys creating native landscapes for customers, she truly loves bigger restoration projectsâthe ones that include tamarisk and Russian olive removal. Wildland Scapes provides equipment and expertise to Rim to Rim Restoration, a project-based non-profit which works with entities including the Nature Conservancy and the BLM to remove invasive species.
"I'm a self-certified plant geek, and in particular I have a bias toward native plants. But the reason I have a bias toward native plants is they've evolved with the wildlife here," she said. "If you have all tamarisk, you have less of the native insects and birds and whatnot. From my understanding, from the reading I've done, is it's a much less diverse habitat if it's dominated by tamarisk or Russian olive."
Dohrenwend's experience with the plant's limiting effect on diversity goes well beyond reading.
"I've seen that in areas where you try to crawl through them; there's nothing there in tamarisk," she said. "You don't even see mice in there. When you remove the tamarisk from the area you start to see other animals, other birds, other things going on."
The tamarisk is also credited with a major engineering feat, the channelization of the Colorado River. Dense stands of the plant along the river's banks are blamed for limiting the river's natural tendency to spread. Dohrenwend says that effect is subject to some debate.
"It's an artificial assumption that the river should stay in this channel that the tamarisk helps us build," she said, though she adds that the tamarisk isn't the sole culprit in taming the river. The Colorado may be undammed as it runs through Moab, but it's not uncontrolled.
"We don't have the river system that we once did because it doesn't have the flood flows," Dohrenwend said. "From what I've read, it's not entirely the tamarisk that's created [channelization], it's a combination of the tamarisk and the controlled flows. You've got a lot of draws for irrigation, so you're not getting the same flows at all. The 100,000 [cubic feet per second] flows, which have happened (in the past), aren't going to happen with all those draws."
Before the tamarisk, the river was lined with willows and grasses. The willows were more compliant during the Colorado's periodic high-water events.
"What it does that tamarisk doesn't is it lies down in a flood," Dohrenwend said. "So the roots are protecting the bank, while the foliage and the branches lie down. Tamarisk doesn't do that; it sticks up. What happens is it creates turbulence in the water, it slows down and drops sediment and builds banks up."
From those banks, a mature tamarisk can soak up over a hundred gallons of water a day. At the same time, it raises the salinity of the surrounding soil, rendering it unusable for native seeds. Over time, as it has on the Colorado, it can take over an entire ecosystem.
"Thirty years ago when I used to drive up and down the (Colorado) river road, you could see the river," Eleanor Bliss remembers. As executive assistant for the Grand Canyon Trust, Bliss is also part of the Southeastern Utah Tamarisk Partnership, a coalition of government and non-profit groups devoted to controlling the plant.
"It was probably after the big high water year (1984) that was when there was a huge planting on some of the higher ground and they really started to capture the river bank," she said. "I don't think they had really taken over the riverbanks until the last 20 years. There were big sandy beaches, open stands of cottonwoods, a much more open feel."
That's because the indigenous vegetation isn't as opportunistic.
"With willow and conttonwood and other species, they don't have as broad a happy place to live," Dohrenwend explained. "You'll see a thicket of tamarisk, it can go not quite to the low flow level of the river, but pretty close, and it will go way up onto a bank or a bench 15 feet above the river. The willow might be a thicket of just willow, but it's going to be fairly narrow and fairly close to the river."
With all the issues surrounding tamarisk, a wide range of groups and agencies have come together to address the issue. The Bureau of Land Management, the National Park Service, the Nature Conservancy, the Grand Canyon Trust, Utah State University, and Grand County are all working toward the common goal of controlling tamarisks. No one suggests eradication is possible.
However, control efforts are promising. Four years ago USU and Grand County released tamarisk beetles, a small Asian beetle which feeds on the tamarisk. The bug has been extremely successful, establishing a wild population up and down the Colorado River corridor, and leaving brown, dying tamarisks behind.
BLM crews have been removing some of the dead tamarisks.
"What we saw this year was the BLM going out and making fire breaks and tending to their camp areas," Bliss said. A Castle Valley resident, Bliss watched the effort progress, with crews slashing and burning the ground between the road and the river.
"What I saw, besides the big fire rings, I saw the river, and that was pretty powerful for me, to see that come back," Bliss said. "Almost the whole drive you can see the river. That's something that's changed dramatically in a really short period of time."