Ulmus pumila, the Siberian elm, is a tree native to Asia. It is also known as the Asiatic elm and dwarf elm, but sometimes mistakenly called the "Chinese" elm (Ulmus parvifolia). U. pumila has been widely cultivated throughout Asia, North America, Argentina, and southern Europe, becoming naturalized in many places, notably across much of the United States.
Description The Siberian elm is usually a small to medium-sized, often bushy, deciduous tree growing to 25 m (82 ft) tall, the diameter at breast height to 1 m (3 ft 3 in). The bark is dark gray and irregularly longitudinally fissured. The branchlets are yellowish gray, glabrous or pubescent, unwinged, and without a corky layer, with scattered lenticels. The winter buds are dark brown to red-brown, globose to ovoid. The petiole is 4–10 millimetres (1⁄4–1⁄2 inch) and pubescent; the leaf blade is elliptic-ovate to elliptic-lanceolate, 2–8 by 1.2–3.5 centimetres (3⁄4 in–3+1⁄8 in × 1⁄2 in–1+3⁄8 in), the colour changing from dark green to yellow in autumn. The perfect, apetalous, wind-pollinated flowers bloom for one week in early spring, before the leaves emerge, in tight fascicles (bundles) on the last year's branchlets. Flowers emerging in early February are often damaged by frost (causing the species to be dropped from the Dutch elm breeding programme). Each flower is about 3 mm (1⁄8 in) across and has a green calyx with four or five lobes, four to eight stamens with brownish-red anthers, and a green pistil with a two-lobed style. Unlike most elms, the Siberian elm is able to self-pollinate successfully. The wind-dispersed samarae are whitish tan, orbicular to rarely broadly obovate or elliptical, 1 cm–2 cm × 1 cm–1.5 cm (3⁄8 in–3⁄4 in × 3⁄8 in–5⁄8 in), and glabrous except for pubescence on the stigmatic surface; the stalk is 1–2 mm (5⁄128–5⁄64 in), and the perianth is persistent. The seed is at the centre of the samara or occasionally slightly toward the apex, but does not reach the apical notch. Flowering and fruiting occur from March to May. Ploidy: 2n = 28. The tree also suckers readily from its roots. The tree is short-lived in temperate climates, rarely reaching more than 60 years of age, but in its native environment, may live between 100 and 150 years. A giant specimen, 45 km (28 mi) southeast of Khanbogt in the south Gobi, with a girth of 5.55 m (18 ft 3 in) in 2009, may exceed 250 years (based on average annual ring widths of other U. pumila in the area).
Taxonomy The species was described by Peter Simon Pallas in the 18th century from specimens from Transbaikal. Two varieties were traditionally recognized: U. p. var. pumila and U. p. var. arborea, but the latter is now treated as a cultivar, U. pumila 'Pinnato-ramosa'.
Distribution and habitat The tree is native to Central Asia, eastern Siberia, the Russian Far East, Mongolia, Tibet, northern China, India (northern Kashmir), and Korea. It is the last tree species encountered in the semidesert regions of Central Asia.
Ecology
Pests and diseases The tree has considerable variability in resistance to Dutch elm disease; for example, trees from north-western and north-eastern China exhibit significantly higher tolerance than those from central and southern China. Moreover, it is highly susceptible to damage from many insects and parasites, including the elm leaf beetle Xanthogaleruca luteola, the Asian 'zigzag' sawfly Aproceros leucopoda, elm yellows, powdery mildew, cankers, aphids, leaf spot and, in the Netherlands, coral spot fungus Nectria cinnabarina. U. pumila is the most resistant of all the elms to verticillium wilt.
Invasiveness and spontaneous hybridization In North America, U. pumila has become an invasive species in much of the region from central Mexico northward across the eastern and central United States to Ontario, Canada. It also hybridizes in the wild with the native U. rubra (slippery elm) in the central United States, prompting conservation concerns for the latter species. In South America, the tree has spread across much of the Argentine pampas. In Europe, it has spread widely in Spain, and hybridizes extensively there with the native field elm (U. minor), contributing to conservation concerns for the latter species. Research is ongoing into the extent of hybridisation with U. minor in Italy. In the Netherlands, 1700 Siberian elms planted in error for field elm in 2016 in the Zalkerbos near Kampen, Overijssel, were grubbed up because of invasiveness concerns and replaced in 2023 with native species. U. pumila is often found in abundance along railroads and in abandoned lots and on disturbed ground. The gravel along railroad beds provides ideal conditions for its growth - well-drained, nutrient-poor soil, and high light conditions; these beds provide corridors that facilitate its spread. It is found as high as 8000 feet in the Sandia Mountains in New Mexico and is invading coniferous forest there. New Mexico may be a center of genetic diversity in North America. Owing to its high sunlight requirements, it seldom invades mature forests, and is primarily a problem in cities and open areas, as well as along transportation corridors. The species is now listed in Japan as an alien species recognized as established in Japan or found in the Japanese wild.
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