Five trees introduced into this area have been especially important in the botany of the area, and have caused residents problems. They are Elms (Ulnus spp.), Tree of Heaven (Ailanthus altissima), Black Locust (Robinia pseudoacacia), Russian Olive (Eleagnus angustifolia) and Fremont Cottonwood (Populus fremontii). The first four trees have escaped cultivation and frequently appear in landscapes as weed trees.

There are three Elm species commonly found in northwestern Nevada today. These are American Elm (Ulmus americana), Siberian Elm (Ulmus pumila ) and Chinese Elm (Ulmus parvifolia), and they all interact differently with the environment.

American Elm, a native of the eastern U.S., is a beautiful landscape tree when healthy. Migrants from the eastern part of the U.S. planted these trees to make vase-shaped archways for city streets; many old American Elms can be seen lining older streets in Reno and Carson City. Unfortunately, the tree is susceptible to Dutch Elm disease, and the ranks of these majestic trees have been decimated.

Siberian Elm, a native of Siberia, was introduced into the U.S. in the 1860s. It soon established itself as a pest of riparian areas throughout the U.S. It has a couple of bad problems: first, its branches are brittle and break in strong winds (which we have here in northwestern Nevada), causing problems with litter; second, although more resistant to Dutch Elm Disease than the American Elm, it still shows some susceptibility; third, it is extremely susceptible to attack by Elm Leaf Beetles, which turn the green leaves into a brown lacework by the end of summer (rendering the tree pretty ugly). It also grows wherever it can find water, so it is even found where there is no irrigation. It is considered a weed tree in many states. The trees hold fast to the soil and are difficult to remove.

Chinese Elm, a native of China, is a smaller tree than the other two, with a similar shape. However, it is much more resistant to both Dutch Elm Disease and Elm Leaf Beetles. In the future, this may become the predominant elm planted in northwestern Nevada.

This tree, a native of China, was first introduced into the U.S. in 1784, and was probably used by Chinese people working in California for medicinal purposes. It is considered as a weed tree in most of the U.S. It suckers freely and grows wherever it can find water. It is profuse along the Truckee River in Idlewild Park, Reno.

Black Locust

Black Locust, a native of eastern North America, is also a riparian tree. It was planted by western pioneers. It propagates both by seed and root suckers. When a mature tree is cut down, many new plants sprout from the roots. It is considered a weed tree by many states.

Russian Olive, a native of southern Europe and Asia, was introduced into the U.S. somewhere around 1900. It was used for windbreaks, erosion control etc. After a couple of decades it escaped, and outcompeted other landscape trees. It is classified as a noxious weed in Colorado and New Mexico. It mainly propagates by seed, but it is drought-tolerant and can spring up in non-riparian areas.

Fremont Cottonwood is actually a native of a small area of northwestern Nevada. It was discovered by Col. John C. Fremont at Pyramid Lake in Washoe County. As opposed to the more widely native Black Cottonwood (Populus trichocarpa), it grows more rapidly, has larger leaves, and has better yellow fall color; it actually is close in appearance to the Plains Cottonwood (Populus deltoides).

It was early planted in non-native areas, as evidenced by the fact that Fremont Cottonwoods were planted around the oldest building still standing in Washoe County, erected in 1864. The tree spreads readily, and can be found in every riparian (streamside) area in northwestern Nevada.