Slippery elm, known scientifically as Ulmus rubra, is a recognizable deciduous tree species across North America. It has long been a part of the continent’s natural landscape, spanning a wide geographic range.
Understanding Slippery Elm
Slippery elm is a medium-sized deciduous tree native to eastern North America, growing from southeastern North Dakota east to Maine and southern Quebec, and south to northern Florida and eastern Texas. It typically reaches heights of 12 to 19 meters (39 to 62 feet). The tree’s bark is gray with distinct ridges and furrows, revealing a reddish-brown inner layer.
Its leaves are broad, oblong, or obovate, measuring 10 to 20 centimeters (4 to 8 inches) in length. They have a rough, sandpapery texture on their upper surface and are velvety underneath, with doubly-serrated margins. The inner bark produces a mucilaginous substance, which gives the tree its common name due to its slick feel when wet. Historically, this inner bark was used in traditional medicine for soothing sore throats and digestive issues, and as a food source in times of scarcity.
Its Conservation Status
The conservation status of slippery elm (Ulmus rubra) is a topic of frequent discussion. The International Union for Conservation of Nature (IUCN) Red List currently categorizes Ulmus rubra as “Least Concern.” This classification indicates the species is widespread and abundant, not meeting criteria for a threatened category. While some sources suggest “Near Threatened,” the global assessment remains “Least Concern.”
The IUCN defines “Near Threatened” as a species that may become vulnerable in the near future but does not yet qualify as threatened. This status signifies that while not currently endangered, its population trends or existing pressures warrant close monitoring. Although the global status is “Least Concern,” regional or state-specific classifications can vary, reflecting localized pressures or population declines. For example, in Maine, slippery elm has been categorized as historical or potentially extirpated.
Challenges and Conservation Efforts
Despite its “Least Concern” global status, slippery elm populations face several challenges that contribute to regional declines. A primary threat is Dutch elm disease (DED), caused by the fungal pathogens Ophiostoma ulmi and Ophiostoma novo-ulmi. Although slippery elm exhibits more resistance than American elm, it is still susceptible to this disease, which disrupts the tree’s water transport system, leading to wilting and eventual death. Another disease, Elm Yellows, caused by a phytoplasma, also impacts slippery elm and can lead to significant tree decline.
Habitat loss further contributes to pressure on slippery elm populations, as forests and floodplains are converted for development or agriculture. Unsustainable harvesting practices also pose a substantial risk. The inner bark, traditionally used, is typically removed by girdling, which can kill the tree. Significant quantities of slippery elm bark are traded; for example, over 300,000 pounds were purchased by American Herbal Products Association members in 2010. Such demand can lead to over-exploitation if not managed carefully.
Conservation efforts for slippery elm include:
Developing and planting disease-resistant strains to combat DED and Elm Yellows.
Promoting sustainable harvesting methods, such as removing only thin vertical strips from live trees or limiting collection to branches and dying trees.
Undertaking cultivation projects to reduce reliance on wild-harvested trees.
Implementing habitat protection and proactive monitoring networks.
Distributing seeds from potentially resistant trees to safeguard the species.