TREE OF HEAVEN – NOT SO HEAVENLY

by

Barbara Bania

University of California Cooperative Extension/El Dorado Master Gardener

Have you recently noticed some tall sticklike plants with a bunch of reddish leaves sprouting from the top like flowers at the top of a tall stem? At this time of year, that’s what a young Tree of Heaven (Ailanthus altissima) looks like. Even on mature trees the leaves sprout from the tips of the branches, as opposed to along them – a very distinctive feature. These deciduous invasive “weed” trees are found throughout our foothills and are on the El Dorado County Noxious Weed Management Group’s list of most unwanted plants. Additional common names for this plant include stinking sumac (because the flowers of the male tree have an unpleasant odor), Chinese sumac, and copal tree.

Tree of Heaven is native to central China and was brought to California primarily by Chinese workers during the gold rush era. It is an attractive tree and, in some parts of the country where the natural growing conditions keep it under control, it is sold as an ornamental landscape tree. It is found in 42 of our 58 states, quite a testimony to its tenacity and adaptability. The pinnate leaves are 1 – 3 feet long and divided into 13 – 25 leaflets that are each 3 – 5 inches long. It might be confused by the casual observer with the Chinese pistache (planted at the Highway 50/Forni Road interchange) which also has reddish pinnate leaves unfurling at this time of year. The Chinese pistache, however, has a more rounded shape and the leaves appear all along the branches instead of just at the tips.

Why is Tree of Heaven classified as a noxious plant here? It’s because they like the growing conditions so much that they multiply to the point of destroying natural habitat, impacting native plants and wildlife, intruding onto farm/range lands, and overtaking home landscapes. A good example of out-of-control growth can be seen along Highway 50 about 6 miles west of Placerville, surrounding the sign “Shingle Springs Drive (Exit 39) 1 mile”. The California Department of Transportation (Cal Trans) had to cut down the trees that were blocking the sign but a dense grove still remains. I walked over there a couple of weeks ago to take a look at eradication efforts and found hundreds of baby trees sprouting up where larger ones had been cut down. The trees have even spread to the south side of the freeway and are beginning to establish themselves there. You don’t even have to drive by this site to see invasive stands of Ailanthus – there are significant stands along quite a few roads throughout the county, along the El Dorado Trail, and even along Highway 50 in downtown Placerville.

Several traits contribute to its invasiveness. The most easily observed is its seed production. One of the features of this tree is the profusion of tan 5” long seedpods; an individual tree can produce 325,000 seeds per year. In addition, this tree is alleopathic, meaning it excretes a toxin that kills other nearby vegetation, reducing the competition for nutrients and water from the soil. They are also prolific root and stump sprouters and are difficult to control once established. The best method of control is to dig out the baby trees before they establish a long, thick tap root. Cutting larger trees down in the spring, before they flower, will also reduce seed production and may reduce their overall vigor. An article addressing other methods of control, including herbicides, will be published later this year when the trees are approaching the weakest point of their growing cycle and eradication efforts can be maximized.

The following are some suggestions to help protect El Dorado County from this invasive species. If the plant is growing on your property, try to eradicate it; do not give anyone seeds; and do not encourage wildlife to your yard because animals can spread the seeds elsewhere. Even if you think the trees are pretty and want to include them in your landscape, please do not do so. There are other trees with pinnate leaves suitable for this area that provide the same quality of dappled shade (such as Chinese pistache, black walnut, pecan, and mountain ash) which are much more well-behaved. Educating others by sharing this is article with them can also help reduce the impact of this aggressive plant.