Simaroubaceae | Pest Rating Proposals and Final Ratings

California Pest Rating for

Tree of Heaven | Ailanthus altissima (Miller)

Family: Simaroubaceae

Pest Rating: C | Proposed Seed Rating: R

PEST RATING PROFILE

Initiating Event:

This plant has been included on the CDFA noxious weed list.

History & Status:

Background: Tree of heaven is a (mostly) dioecious, medium-sized tree that grows to approximately 30 meters high. The long (>50 cm), pinnately compound leaves contain 13-25 lanceolate leaflets measuring 8-13 centimeters each. Fruits are produced in large clusters and are winged, facilitating dispersal via wind. The tree can root sprout vigorously, especially when damaged, forming thickets of 100s of stems covering over 0.4 hectares. Tree of heaven was planted extensively in the early days of California and many of these plants have persisted as clonal clumps or thickets.

Worldwide Distribution: Tree of heaven is native to China and has been introduced to many temperate localities throughout the world, including the United States.

Official Control: This tree is listed as a noxious weed by at least five states (California, Connecticut, Massachusetts, New Hampshire, Oregon, and Vermont).

California Distribution: Tree of heaven is widespread in California; it has been reported in 39 counties (Alameda, Amador, Butte, Calaveras, Contra Costa, El Dorado, Fresno, Humboldt, Inyo, Los Angeles, Kern, Marin, Mariposa, Mendocino, Monterey, Napa, Nevada, Orange, Placer, Riverside, Sacramento, San Bernardino, San Diego, San Francisco, San Joaquin, San Luis Obispo, San Mateo, Santa Clara, Santa Cruz, Siskiyou, Solano, Sonoma, Stanislaus, Sutter, Trinity, Tuolomne, Tulare, Ventura, and Yolo).

California Interceptions: Tree of heaven is submitted to the CDFA Botany Lab about once a year for identification.

The risk tree of heaven would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: It is apparent that tree of heaven can tolerate the conditions found throughout much of the state of California, because it is already present over much of the state. Therefore, it receives a High (3) in this category.

Evaluate if the pest would have suitable hosts and climate to establish in California:

-Low (1) Not likely to establish in California; or likely to establish in very limited areas.

-Medium (2) may be able to establish in a larger but limited part of California.

-High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: Tree of heaven does not require any one host, but grows wherever ecological conditions are favorable. It receives a High (3) in this category.

Evaluate the host range of the pest.

-Low (1) has a very limited host range.

-Medium (2) has a moderate host range.

-High (3) has a wide host range.

3) Pest Dispersal Potential: Tree of heaven can reproduce via seed as well as clonally. Seeds are produced in great number (up to one million seeds/tree/year) and can be dispersed via wind. However, it only rarely reproduces by seed in California and then only along riparian corridors. Most populations or clusters of trees are persisting from horticulture. Due to its ability to root sprout, tree of heaven can be very long-lived and hard to eradicate. Therefore, it receives a Medium (2) in this category.

Evaluate the natural and artificial dispersal potential of the pest.

-Low (1) does not have high reproductive or dispersal potential.

-Medium (2) has either high reproductive or dispersal potential.

-High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Tree of heaven can cause damage to structures, etc. in urban areas. The leaves are apparently somewhat irritating to skin. However, there does not appear to be any data quantifying economic damage resulting from this species. Therefore, it receives a Low (1) in this category.

Evaluate the likely economic impacts of the pest to California using the criteria below.

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 1

-Low (1) causes 0 or 1 of these impacts.

-Medium (2) causes 2 of these impacts.

-High (3) causes 3 or more of these impacts.

5) Environmental Impact: Although it is often associated with disturbed or urban areas, tree of heaven appears to be able to compete successfully with native plants. Disturbed and riparian habitats appear to be especially threatened. Impacts in California are unknown, but this tree is common in riparian areas and may be displacing native plants. Characteristics of tree of heaven that could allow it to displace native flora include clonal reproduction and allelopathic chemicals found in its tissues, which have been shown to inhibit germination and growth of other plants. Tree of heaven is considered an invasive wildland pest plant by the California Invasive Plant Council. Therefore, it receives a High (3) in this category.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: A, C

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score: 3

-Low (1) causes none of the above to occur.

-Medium (2) causes one of the above to occur.

-High (3) causes two or more of the above to occur.

Consequences of Introduction to California for tree of heaven: Medium (12).

Low = 5-8 points

Medium = 9-12 points

High = 13-15 points

6) Post Entry Distribution and Survey Information: Tree of heaven is already present over much of California. Therefore, it receives a High (-3) in this category.

Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

The final score is the consequences of introduction score minus the post entry distribution and survey information score: Medium (9)

Uncertainty:

Although tree of heaven has been present in the United States for a long time, it appears to still be spreading in the western part of the country, including California. The full impact of this species, especially in riparian areas, may be yet to be seen. However, unlike in eastern North America, there is little indication that tree of heaven commonly established via seed in California.

Conclusion and Rating Justification:

Tree of heaven may be a serious threat where it has been planted in the past, especially in riparian areas. However, it is already widely distributed across the state. A “C” rating is justified.

References:

Calflora http://www.calflora.org

California Invasive Plant Council. http://cal-ipc.org

Consortium of California Herbaria. http://ucjeps.berkeley.edu/consortium

Encyclaweedia. https://www.cdfa.ca.gov

Jepson eFlora. http://ucjeps.berkeley.edu/eflora

Kowarik, I. and I. Säumel. 2007. Biological flora of Central Europe: Ailanthus altissima (Mill.) Swingle. Perspectives in Plant Ecology. 8: 207-237.

Lawrence, J.G. 1991. The ecological impact of allelopathy in Ailanthus altissima (Simaroubaceae). American Journal of Botany. 78(7): 948-958.

Oregon Department of Agriculture, Noxious Weed Control Program http://www.oregon.gov/oda/shared/Documents/Publications/Weeds/TreeOfHeavenProfile.pdf

United States Department of Agriculture, Plants database. https://plants.usda.gov

United States Forest Service, Fire Effects Information System. https://www.feis-crs.org/feis/

Author:

Kyle Beucke, 1220 N Street, Room 221, Sacramento, CA, 95814, 916-403-6741, plant.health[@]cdfa.ca.gov

Responsible Party:

Dean G. Kelch, Primary Botanist; California Department of Food and Agriculture; 1220 N Street, Sacramento, CA 95814; Tel. (916) 403-6650; plant.health[@]cdfa.ca.gov.

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