Ulmus pumila -- Arizona

Siberian elm is native to northern Asia and was introduced in North America in the 1860s. It has been planted throughout the Midwest and Great Plains for windbreaks and lumber. Siberian elm invades pastures, roadsides, and prairies throughout the Midwest and Great Plains regions of the United States. The trees are drought and cold resistant, allowing them to grow in areas where other trees cannot (Extension.org, 2019). Siberian elm has naturalized in nearly all counties in Indiana (Jacquart et al. 2007). It has also invaded Argentina (Hirsch & Hensen, 2010). Ulmus pumila is considered an invasive tree in 41 of the United States (Zalapa et al. 2010).

Ulmus pumila is widely reported as invasive in North America, including western states (Perry et al. 2018, Reynolds et al. 2022) and Texas (TexasInvasives, 2023). The species is listed as a Class C noxious weed in New Mexico (Ashigh, et al. 2009). It is noted as naturalized in Yavapai Co, Arizona (Halldorson, 2022). It has also invaded Argentina (Hirsch & Hensen, 2010), which is mostly a climate match for Arizona.

Ulmus pumila is today regarded as naturalized or invasive in most regions where it has been introduced. Its invasion success can partly be explained by inter- and intraspecific hybridization, leading to high genetic diversity in the corresponding non-native populations (Hirsch et al. 2016). Hirsch makes the distinction between naturalized and invasive, and indicates U. pumila can be naturalized and can also reach the magnitude of invasive. Siberian elm is listed as a Class C Noxious Weed in New Mexico (Beck & Wanstall, 2022).

The Siberian elm is a native of relatively moist regions of East Asia, but occurs westwards up to the dry Gobi desert, where it is bound to water surplus sites and oases. In North America, the Siberian elm was widely planted on the plains as a fast growing
windbreak or shady tree, and naturalized populations can be found along river banks as well as on dry sites. Furthermore, this species spreads in the Argentinean Pampa where it colonizes old field and grasslands (Hirsh & Hensen, 2010). Siberian elm appears more characteristic of colder and less xeric regions than Arizona, but Arizona contains upland plains with cold winters as well. Siberian elm is listed as a Class C Noxious Weed in New Mexico. Class C species are widespread in the state (Beck & Wanstall, 2022).

The Chinese elm, Ulmus parvifolia can naturalize (reseed) in heavily and not so heavily irrigated landscapes in Phoenix and southern California (Martin, 2023). However this plant would not appear to meet the definition of invasive used by the PRE.

Ulmus pumila is found widely across northern Eurasia. It is naturalized across most of the USA and into Canada. It has some limited naturalization in Mexico and South America. It is not shown as present in climate-matching areas of Africa, Australia or the Middle-East (GBIF, 2017). The Siberian elm is a native of relatively moist regions of East Asia, but occurs westwards up to the dry Gobi desert, where it is bound to water surplus sites and oases (Hirsh & Hensen, 2010). The Siberian elm appears to have considerable adaptability to a variety of climates, but it is not found predominately in a climate matching Arizona.

Siberian elm is an invasive tree that forms dense thickets, shading and crowding out native plants, thereby reducing forage for wild animals and livestock (Extension.org, 2019). It quickly out-competes desirable native plants, especially in sparsely vegetated or disturbed areas (USDA, 2014).

A prescribed burn may be used in certain fire-adapted areas to remove and suppress top growth. Depending on fire intensity, burning will control seedlings, but saplings and older trees will usually survive and regrow from the root system (USDA, 2014). This account suggests the plant is not flammable and does not promote a fire regime. It also suggests that seedlings have vulnerability to fire. No sources were found that refer to the plant changing fire frequency or intensity.

Siberian elm forms dense thickets that close open areas and displace native plants, thereby reducing forage for wild animals and livestock (Extension.org, 2019). By inference, this could impact grazing systems.

Siberian elm forms dense thickets that close open areas and displace native plants, thereby reducing forage for wild animals and livestock (Extension.org, 2019). By inference , it could slow or block the movement of larger animals.

Reproduces primarily by seed; roots resprout when top growth is damaged. Trunks may be cut close to the ground to remove top growth. Anticipate that trunk and root resprouts will return later in the growing season (USDA, 2014). Ulmus pumila will resprout from the roots following damage to or cutting of the main stem, but this is not a significant mechanism of spread (Wesche et al. 2011).

Reproduces primarily by seed; roots resprout when top growth is damaged (USDA, 2014). Reproduction by fragmentation is not mentioned in the literature on Siberian elm reproduction.

Germination rate is high and seedlings soon establish in the bare ground found early in the growing season (TexasInvasives, 2023). Seeds of non-native populations of the woody Siberian elm, Ulmus pumila, germinated faster than those of native populations (Hirsch et al. 2016).

Jacquart et al. (2007) state that “[e]ven small trees can have >1,000 seeds.” This seems reasonable for mature trees, but the references provided by the authors either don’t support this assertion quantitatively or could not be found. Thus confidence for this answer can only be Medium.

Wesche et al. (2011) reported germination rates of 48-74% (depending on substrate type) for U. pumila in field tests within the species native range in Mongolia. Given the high germination rates reported from laboratory studies (74-89 %; Hirsch et al. 2012, Song et al. 2011) it seems reasonable to infer that > 25% of seeds would germinate in the wild given appropriate substrate, temperature, and moisture habitats within the species’ naturalized range.

Ulmus pumila is listed as requiring 8 years to be minimum seed-bearing age (Bonner & Karrfalt, 2008). Ulmus pumila can produce seed in as few as 10 years (Zalapa et al. 2010).

Clusters of smooth, circular, winged, samara-type fruit with single seed in center occur from April to May (USDA, 2014).

Siberian elm seed is primarily dispersed via wind, although seed may also be transported by water and animals (USDA, 2014). Detail is not available concerning the mode or distance of animal dispersal.

Wind carries seed to distant areas where new colonies can form. Seeds are produced early in spring and spread by the wind (TexasInvasives, 2023). Siberian elm seed is primarily dispersed via wind, although seed may also be transported by water and animals (USDA, 2014). Field studies by Blass et al. (2010) found windborne dispersal of U. pumila seeds exceeded 100 m. The authors also found that 99% of U. pumila seeds remained afloat in water for 24 hours, suggesting a capacity for long-distance water-borne dispersal.

Seed may be carried long distances by adhering to surfaces and undercarriages of logging equipment and vehicles (USDA, 2014).