| 0 | Ames 36073 | JDC/UT/2022/028/1009 | Ulmus thomasii Sarg. | Iowa, United States | NC7 |  | | 2023 | COLLECTED | 06/05/2023 | Ledges State Park approximately 4.75 miles south of Boone, T83N R26W (Madrid NW Quad.) near center of SE ¼ Sec. 16 and also NW ¼ SW ¼ Sec. 21. | 41.99780200, -93.87967900 | 288 | Moist deciduous woods typically on mid-slopes to base of slopes and also well-drained floodplains. | Wild material | Ulmus thomasii (Rock elm) is an underutilized tree species both in conservation and in the urban landscape. Charles Sprague Sargent (first director of the Arnold Arboretum of Harvard University, Boston, MA) described the wood of Rock Elm as "heavy, hard, very strong and tough, closely grained, and susceptible of receiving a beautiful polish". Historically noted for a variety of uses in woodworking including furniture, heavy agricultural implements, timber frame buildings, pianos, hockey sticks, and hand tools. U. thomasii is extremely drought tolerant, adaptable to very calcareous soils, and compared to U. americana or U. rubra has a very conservative growth rate requiring minimal attention in regards to pruning. Rock elm naturally tends to develop into a nice structural specimen in the landscape, unlike other fast growing U. americana cultivars in the nursery trade needing frequent attention. Rock elm has very fissured bark and is well known for maintaining a strong central leader resulting in a very attractive, pyramidal form. Despite many literature sources stating that "wings" on the stems are a key identifiying characteristic, this trait is not reliable and many genotypes may completely lack "wings" on the stems. While growth habit and morphology of dormant buds (very pointy) are good traits to help aid in identification, fruits are the best way to confirm identity. Fruits are densly pubescent, often described as "inflated" and generally reach maturity a couple weeks after U. rubra and U. americana. U. thomasii flowering in central Iowa typically occurs the last week in April into the first week in May and are rather distinguishable from other Ulmus in being pendulous. Fruits are extremely prized treats for many birds, where fruits are often "robbed" prior to full maturity. Fruits are also highly prized by many other animals such as mice, squirrels, chipmunks, turkeys, etc. and are generally consumed within hours after fruit abscission. The native range of U. thomasii is concentrated in the northeastern United States and into Canada with disjunct populations documented in northwestern Missouri and northwestern Arkansas (Little, E. L. Jr. 1971). In the 1895 Silva of North America (vol. 7) it was stated that, “The value of the wood of the Rock Elm threatens its extinction and most of the large trees have already been cut.” Today, since rock elm is rather rare, especially in areas near the edges of its range, many states list the species as endangered or threatened warranting preservation efforts. Genetics of this accession would be representative of the species southwestern edge of its native range. Out of approximately 100 specimens noted throughout Ledges State Park only 1-2% of specimens had characteristic "wings" on the stems. Research was executed (Moore, P., 2024) involving the core sampling of U. thomasii and U. americana specimens in Ledges State Park to make growth ring widths and basal area increment comparisons. Results determined that the average age of cored trees U. thomasii (n=4) and U. americana (n=4) of both species was roughly 80 years, excluding the exceptional case of tree #007 (Ames 36073 23ncao02 SD). Tree #007 was aged at 300 years of age and currently (2025) ranks as the 14th largest U. thomasii in Iowa measuring 21" DBH with a height of 75' 5" and a spread of 43' 5" totalling 152.21 points (Rouw, M., personal communication, 4 May 2022). The computed mean density at 𝑀𝑀 = 12% for U. thomasii was 0.80 g/cm3, and for U. americana was 0.672 g/cm3. These values are both higher than the representative values inferred from the Woods Database which are 0.755 g/cm3 for U. thomasii and 0.56 g/cm3 for U. americana. To date, there is little to no information regarding U. thomasii resistance to Dutch Elm Disease. Collections of U. thomasii at the Arnold Arboretum have over-time succumbed to DED (Pruka, B., 2016). However, data recorded by Moore (2024) indicates that U. thomasii growing in central Iowa can surpass 300 years in age verifying it's long-term utilization in the landscape. | 2142915 | Ames 36073 |