Rock elm (ulmus thomasii)

Very rare native tree that must be protected by repopulation reaching 25 m in height and 75 cm in diameter, which can live up to 175 years. This elm does not have the typical shape of the American elm or slippery elm. It has a distinct trunk almost to the top of the tree; dark gray bark, tinged with red, divided into flattened ridges separated by irregular and discontinuous furrows. Cylindrical to oval crown; main branches rather short, the lower ones often inclined or more or less horizontal, appearing gnarled, covered with corky ridges giving the crown a bushy appearance. Branches pubescent, blackish and with crisscrossed crests appearing during the second season. Leaves alternate, oblong to obovate, shortly acuminate, leathery and with curved teeth and provided with about 20 pairs of secondary veins; upper surface dark green, shiny, glabrous or almost, occasionally rough; underside paler, slightly pubescent. Bright yellow fall coloring. Flowers in clusters. Fruit: an elliptical to oval samara, 10 to 20 mm long and 7 to 15 mm wide, broadly winged and pubescent; swollen seed. Of all the species of elm, this one has the hardest wood.

Special situation: to date, 69 occurrences of cork elm have been recorded for Quebec, Canada. Of these, five no longer exist and 10 are historical (the last observations date back more than 25 years). Recent occurrences mostly correspond to small populations or isolated individuals found in urbanized areas. According to a recent inventory, the total number of cork elms in Quebec is estimated at approximately 4,000. The species is in decline there, as in a large part of its range. Urban and agricultural development, quarrying, accidental cutting of individuals or forestry practices unfavorable to the regeneration of the species constitute the main threats to the survival of this tree. Additionally, mature individuals are often affected by Dutch elm disease. Two occurrences are in protected areas and a third is in a site recently acquired by a conservation organization.

Designated a threatened species in Quebec in 2005, the cork elm and one of its habitats are protected under the Act respecting threatened or vulnerable species. According to data from the NatureServe network, the cork elm is in a precarious situation in 9 of the 24 American states where it is present; it is very threatened in Illinois, Kansas, New Jersey and Ohio; it is threatened in Arkansas, Missouri, Nebraska and New York; and it is vulnerable in Iowa.