(Tree-of-Heaven – Ailanthus altissima) List the top two…

(Tree-of-Heaven – Ailanthus altissima)
List the top two biological/ecological characteristics of this plant that allow it to successfully invade the Los Angeles River Watershed. For each characteristic, explain why this makes this plant a cause for concern. Be sure to support your argument with specific evidence from the plant profile you read and what you know about the ecological and environmental characteristics of the Los Angeles River Watershed from the Biomes lesson.
What is the most important reason that your species should be eradicated? Explain your answer, considering both the environmental and economic impacts described in the plant profile.
Which method of eradication would you be most likely to recommend and why? Which method of eradication would you be least likely to recommend and why? Do you think any of these methods are likely to be effective in eliminating your species? Support your argument with specifics from the plant profile.
Geographic origin: Native to northern and central China
Method of introduction to CA: It was introduced as a landscape ornamental but escapes gardens and spreads by seeds and creeping roots that produce many suckers.
Identifying characteristics: Deciduous tree up to 90 ft. Large (up to 3 feet!) pinnate leaves and small white to greenish flowers ¼ in. wide, arranged in branched clusters 3-5 in. Bark, crushed leaves, and flowers have a distinct odor, that some describe as unpleasant while others describe it as peanut butter or popcorn smell.
Biology and Ecology
Comparison of the DNA of seedlings from the USA and mainland Chinese seed sources, Feret and Bryant (1974). concluded that significant alterations of genetic content have occurred since the introduction and naturalization of A. altissima in the USA 200 years ago. However, there was no evidence of inbreeding depression in the American seedlings and they appeared to be as genetically variable as the Chinese seedlings.
Physiology and Phenology
The tree bears unisexual flowers on different trees. Both male and female flowers appear during July to August. Flowering occurs during May to June and seeds ripen in large, crowned clusters in September to October of the same season, and are dispersed from October to the following spring. A. altissima has good drought resistance as it can reduce transpiration at the hottest point of the day, and use a structure that permits the rapid transfer of water from the roots to the leaves, both of which have contributed to its success in California (Lepart et al., 1991).
Reproductive Biology
Flowers are unisexual, and a single tree can produce up to 1 million wind-dispersed seeds in a year (Weber, 2003). Seeds may be dispersed long distances from the parent plant by the wind, and also by water and road traffic as secondary dispersal mechanisms (Kota, 2005.; Kowarik and Lippe, 2006, 2011; Kaproth and McGraw, 2008.; Säumel and Kowarik, 2010). Intentional introduction has been the common means of long-distance dispersal, introduced to North America, Europe, and Australasia for timber, shade, and urban amenity plantings.
Within a short period of time, one tree can “scatter seed for blocks around and can create a thicket of sprouts from its wide-spreading roots.” One tree produces up to 1,000,000 seeds per year, sprouting from roots. These seeds are easily airborne and can be transported by water and birds as well. Most new shoots are root sprouts, mature trees send up extensive root suckers and sprouts from cut stumps. Sapling growth can reach 3-4 feet a year and can outgrow nearly any native tree, outcompeting natives for light. The roots give off a toxin that acts as a herbicide that can kill or inhibit the growth of other plants (Hoshovsky, M. 1988).
Environmental Requirements
Found primarily in disturbed areas, of both human and natural origin. Is capable of clonal growth into the undisturbed forest. Found in areas disturbed by humans such as along road cuts and in cities, where it was planted as a landscape tree, as well as in areas of natural disturbance such as riparian areas.
A. altissima is found in temperate to sub-tropical climates, and it tolerates a 4-8 month dry season. It also tolerates heavy frosts, and survives absolute minimum temperatures as low as -35°C. A. altissima grows best on loose and porous soils, but can grow on a variety of soils from sandy or clayey loams to calcareous dry and shallow soils (Kowarik and Säumel, 2007). It can even tolerate barren rocky hills. Frequent fires, or prescribed burning or thinning and burning may increase tree-of-heaven abundance.
Environmental Impact
Displaces native plants. In the USA, from Massachusetts to Texas, A. altissima forms dense thickets that displace native vegetation and is especially invasive along stream banks in California and the west (Westbrooks, 1998). Young trees grow rapidly, out-competing many other plant species for light and space. Toxins produced in the bark and leaves accumulate in the soil and inhibit the growth of other plants (Anon., 2002). In riparian communities, lower plant species diversity was associated to the presence of A. altissima (Constán-Nava, 2012).
Economic Impact
A. altissima is mainly valued for shade, and erosion control, particularly in cities where soils are poor and the atmosphere is smoky. It has also been employed in land reclamation of landfill sites (Lee et al., 1997). The leaves can be used as feed for silkworms.
Methods of Control
Mechanical Control
Very difficult to remove once a taproot has been established
Can persist after burning, cutting, and herbicide treatment and it is recommended that seedlings are removed by hand as early as possible, removing the entire taproot.
Cutting stumps stimulates resprouting instead of eliminating it
The entire root needs to be removed to prevent sprouting and even a small root fragment can produce root sprouts.
Cultural Control
Prescribed fire is not recommended to control tree-of-heaven due to tree-of-heaven’s ability to establish from root sprouts and seed after disturbance
Establishing a thick cover of native trees or grass helps shade out tree-of-heaven and discourages tree-of-heaven regrowth
Establishing native tree seedlings on disturbed sites to help reduce invasion of nonnative tree species such as tree-of-heaven
Chemical Control
Cut stump with chemical application treatment such as the glyphosate herbicide reduces significantly the presence of A. altissima
Stem-injection of herbicide kills A. altissima trees
Biological Control
None discovered
Text modified from: CABI, 2021 .Ailanthus altissima. In: Invasive Species Compendium. Wallingford, UK: CAB International.
Cynthia L. Roye. 2016. Ailanthus altissima. Risk Assessment. From Cal IPC.
Fryer, Janet L. 2010. Ailanthus altissima. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us/database/feis/plants/tree/ailalt/all.html [2021, July 4].
Image Credits
Auckland Museum, CC BY 4.0 , via Wikimedia Commons
“Ailanthus-altissima” Links to an external site. by Luis Fernández García is licensed under CC BY-SA 2.0Links to an external site.
All maps are from iNaturalist
Lesson About Los Angeles Watershed:
Much of southern California, including the Los Angeles River Watershed and the region containing Pasadena City College, can be classified as a chaparral biome. Chaparral is found throughout California, southern Oregon, and northern Baja California, both near the coast and inland. Chapparal plant communities are incredibly biodiverse; in fact, chapparal contains 20% of the plant species in California, despite making up only 9% of the wild vegetation. Chaparral is considered a biodiversity hotspot — with high species diversity that is under threat by human activity. Without all of the roads, freeways, and buildings, the landscape across the Los Angeles basin would be covered with evergreen shrubs, annual flowers, oak trees, and sagebrush.
So, what is the climate like in a chaparral biome? Winters are mild and rainy, with typically 10-20 inches of annual rainfall. The summers are hot and dry, with little to no rain typically occurring between the months of March and October. After many months of heat and no rain, chaparral is most vulnerable to fire in the late summer and fall.
Chaparral characteristically is found in areas with steep topography and shallow stony soils, and the plant community is dominated by drought-tolerant woody shrubs. Most plants that live in chaparral have small leaves. This adaptation prevents the plant from losing too much water through its leaves during the hot summer months. Chaparral plants are often deciduous, meaning that they lose their leaves seasonally (typically in autumn).
(Youtube Name: Valuing Chaparral)

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