Noxious trees and native alternatives


By Ethan Proud
PREVIEW Columnist
Ornamental trees are expensive and most landowners become fairly attached to the trees on their property. That being said, some trees are on the noxious weed list and must be controlled.
To avoid planting a tree that will eventually have to be removed and killed, double-check the noxious weed list that can be found on the Colorado Department of Agriculture website or check with the Archuleta County Weed and Pest Department or Extension office.
Two species of trees that occur in Archuleta County and are designated noxious are Russian olive and salt cedar (tamarisk).
Russian olive trees can grow to 25 feet tall and have silvery foliage. These trees can outcompete and displace native trees such as cottonwoods and also native willows. This impacts wildlife, as Russian olive trees, while providing olive fruits that some animals may eat, are not selected as frequently by animals and may be ignored as a food source. Russian olive trees primarily reproduce by seed, but may also sprout from lateral roots, and felling a tree may not actually kill the plant. Russian olive trees also consume more water than native trees and compete for nutrients.
Salt cedar or tamarisk is an introduced species of tree that can use both surface and ground water, which makes it highly competitive with native species. Thick stands of salt cedar can drastically reduce underground water tables as well as the availability of surface water for other vegetation. These trees can alter the landscape and ecosystem by drying up rivers as well as accumulating salt in the leaves, which are deposited in the soil, making it less hospitable to other plant species. Most wildlife will not feed on salt cedar foliage, though they may nest in thickets. The seeds of salt cedar are not long lived and may only be viable for five weeks, but will germinate within 24 hours of water contact. Trees produce 500,000 seeds and live for up to 100 years. Salt cedar may sprout from the root crown, making cutting a poor control option.
For both Russian olive and salt cedar, an integrated management plan that combines manual removal of plants (including roots), chemical and biological controls is recommended.
Rather than planting invasive weed species, check for Colorado native ornamental trees; they will require much less external input than imported exotic trees and will prove hardier in drought conditions and our cold winters.
When choosing native trees, it is important to look at the native environment; a tree that does well below 5,000 feet in a plains or grassland environment may struggle in Archuleta County.
A few native Colorado trees that may be of interest for landscaping include: corkbark fir, box elder, narrowleaf cottonwood, Colorado spruce, Wasatch maple, thinleaf alder, Rocky Mountain juniper and peachleaf willow.
If you are planting ash trees, it is worth noting that the emerald ash borer, an invasive beetle introduced from China is moving westward across the U.S. and is capable of decimating ash tree populations. It is important to use firewood where you cut it, or treat firewood if taking it across state or even county lines.
Archuleta County Weed and Pest is your local resource for managing noxious weed populations and controlling other pests.