APRIL 2021 | No. 249 Researchers and Students Collaborate to Restore American Elm (Ulmus americana) in the Northeast By Richard W. Harper, Nicholas J. American elm (Ulmus americana) Brazee, Christopher A. Copeland has long been an important cultural and Tara M. McElhinney and historical symbol of the North American landscape (Fig. 1). Its graceful form, fast growth and resilience to harsh growing conditions historically made it an ideal tree species for widespread planting. For decades, American elms lined the streets, parks, and private landscapes of communities throughout the United States, Canada, and Europe. With the introduction of Dutch elm disease (DED), caused by the non-native fungal pathogens Ophiostoma ulmi and O. novo-ulmi around 1930 in Ohio (U.S.), populations of this native tree drastically declined. The absence of medium and large specimens of this tree has created a substantial gap in native forests, particularly in floodplain settings of the Northeast, Midwest, and eastern Canada, where it was considered the dominant, foundational species. Its loss also resulted in Fig. 1. Open-grown American elm a substantial reduction of tree canopy cover in cities and towns. Since (Ulmus americana). Photo: N. its demise was so readily apparent, a heightened sense of urgency Brazee, UMass. occurred in relation to its restoration in the landscape (Jonnes 2016). Management Attempts to protect American elms from DED have traditionally focused on three fronts: vector control of native, European, and banded elm bark beetles Up Ahead: (Hylurgopinus rufipes, Scolytus multistriatus, and S. Schevyrewi, respectively), Elm 1-3 disease management with chemicals (i.e., fungicide injection), and exploitation of Restoration natural host plant resistance (Jin et al. 1996). Species 4-5 Spotlight Host plant resistance research at the From the University of Massachusetts 6-9 Woods In 2016, Drs. Nick Brazee, UMass Beetle Extension and Rick Harper, UMass 10-11 Bites Dept. of Environmental Conservation, Growing and students (Fig. 2) from the UMass 11-13 on Trees Urban Forestry/Arboriculture program established the first American elm Gleanings 13-15 host plant resistance research trials News 15 at the UMass Agricultural Learning On the 16 Center’s Dakin Field (Fig. 3, next Horizon page). One thousand seeds consisting Fig 2. Student planting. Photo: J. Solem, UMass. (Continued on page 2) P A G E 2 A P R I L 2 0 2 1 Restoring American Elm in the Northeast event, where elm failure rate may be two to three times higher than other trees (Giblin & Johnson 2016). A second trend that has been observed is that elm trees may be substantially smaller at the time of failure, compared to other tree species (Giblin & Johnson 2016). Failures seemed to be predominantly associated with poor branch structure, rather than the presence of wood decay (Giblin & Johnson 2016). In fact, examination of urban and suburban American elms using sonic and electrical resistance tomography (Fig. 4) revealed that these trees suffer from a relatively low incidence and Fig. 3. Elm research plot, Dakin Field, UMass Agricultural severity of internal decay (Brazee and Marra Learning Center. Photo: N. Brazee, UMass. 2020 ). As such, special attention will be given (Continued from page 1) to monitoring tree branch habit and growth form at the UMass field trials, with the potential of of four genotypes of American elm purported to attempting to address poor branch attachment be resistant to DED were obtained from the and form through pruning of juvenile trees. USDA Forest Service elm research laboratory in Conclusion Delaware OH. These seeds were planted at the The American elm was designated the official College of Natural Sciences Greenhouses in tree of the Commonwealth of Massachusetts in spring 2016. That autumn, over 200 of these 1941. Since DED established itself in seedlings were transplanted to Dakin Field. In Massachusetts decades ago, it has been 2018, a second cohort of an additional six estimated that localized populations may have American elm genotypes were germinated and been reduced by as much as 80% (Huntley planted in the field by students. These elms 1982). Work with these resistant genotypes by represent crosses of numerous American elm varieties, including ‘New Harmony’ and ‘Valley Forge’, that have demonstrated high levels of DED resistance based on previous research and observation by USDA Forest Service scientists and specialists. As part of this long-term study, researchers and students at UMass will collect growth and survival data during the early seasons of establishment. They will also monitor these trees for structural/aesthetic performance, compatibility with urban environments, response to transplant, and long- term survival. An important consideration among putatively resistant American elm cultivars is their structural integrity. Some commonly used DED- Fig. 4. Dr. Nick Brazee examining Ulmus spp. using sonic resistant cultivars appear to fail at a rate that is & electrical resistance tomography. Photo: R. Harper, substantially higher than other tree species. This UMass. may be especially evident after a wind or storm (Continued on page 3) THE CITIZEN FORESTER Mass. Department of Conservation and Recreation A P R I L 2 0 2 1 P A G E 3 Restoring American Elm in the Northeast (Continued from page 2) Giblin, C.P. and G. Johnson. 2016. Pruning cycles and storm damage: Are young American elms failing passionate specialists and students alike has prematurely? Proceedings of American elm restoration spurred optimism that this iconic tree species program, pp. 130-140. Lewis Center, OH. USDA Forest Service, Northern Research Station. may one day return to its former stature on the landscapes of the Northeast, eastern Canada, Huntley, G.D. 1982. The elm - a resurgent resource or a persistent problem? Proceedings of the Dutch elm and the Midwest. disease symposium and workshop, pp. 103-111. Richard W. Harper, Ph.D., is Extension Associate Winnipeg, Manitoba. Manitoba Department of Natural Resources. Professor of Urban & Community Forestry in the Dept. of Environmental Conservation. Nicholas J. Jin, H., G.R.B. Webster, N.J. Holliday, P.A. Pines and Brazee, Ph.D., is an Extension Plant Pathologist in A.R. Westwood. 1996. An elm bark beetle bioassay for the Center for Agriculture, Food and the residual efficacy of chlorpyrifos and cypermethrin used Environment. Christopher A. Copeland, is a for the control of Dutch elm disease in Manitoba. J. Environ. Sci. Health Part B 31(4): 751-761. Massachusetts Certified Arborist with the University Physical Plant. Tara M. McElhinney, was an Jonnes, J. 2016. Urban forests: A natural history of Undergraduate Student/Researcher in the Dept. of trees and people in the American cityscape. Viking. Environmental Conservation. New York, NY. All authors are affiliated with the University of Acknowledgements: Massachusetts Amherst. USDA Forest Service Elm Research Laboratory, Delaware OH; University of Massachusetts Center for References Agriculture Food & the Environment; University of Massachusetts Department of Environmental Brazee, N.J. and R.E. Marra. 2020. Incidence of Conservation; University of Massachusetts Agricultural internal decay in American elms (Ulmus americana) Learning Center; and Stockbridge School of under regular fungicide injection to manage Dutch elm Agriculture. disease. Arboriculture and Urban Forestry 46(1):1-11. Celebrating Arbor Day Once again, Arbor Day will look different this year, but Arbor Day is April 30, 2021 we’ve got lots of ideas for how your community can safely celebrate. Some Arbor Day celebrations in MA in 2020: • Holding a socially distanced tree planting for a • Planting 1-2 trees using municipal staff (or limited group of volunteers holding a ‘limited’ in-house planting • Virtual program with schools using Zoom or • Conduct a virtual tree tour (Northeastern). another virtual platform • Identifying shade trees with sidewalk chalk • Distributing seedlings (Lowell) Ideas based on suggestions from the Arbor Day Foundation Hold a poetry contest for kids and adults and publish the winners in the local paper ☼ Host a Tree ID Challenge encouraging citizens to send in a photo of themselves with a tree they identified using the “What Tree is That?” guide in exchange for a piece of “swag.” ☼ Host an interactive “Ask the Arborist” Q&A session allowing homeowners to ask tree care questions virtually. ☼ Hold a virtual presentation by a tree expert to inform your community about recommended tree choices. ☼ Invite local youth to submit a tree-related question to your tree warden via email and answer the questions via video posted on your community's website or social media. ☼ Partner with local restaurants to give away free tree seedlings with takeout orders. ☼ Develop and roll out your tree program’s social media pages. ☼ Sponsor one or more teachers in your community to attend an online Project Learning Tree professional development workshop. THE CITIZEN FORESTER Mass. Department of Conservation and Recreation P A G E 4 A P R I L 2 0 2 1 Species Spotlight American Mountain Ash, Sorbus americana By Mollie Freilicher Native to northeastern 20 feet. It is hardy to USDA hardiness zone 2 North American, American and can even grow in cooler parts of zone 6 to mountain ash (Sorbus 7. americana) is a small tree Leaves of mountain ash are alternate and or shrub with clusters of pinnately compound with 11 to 17 leaflets white flowers, showy red (including a terminal leaflet), one-and-a- fruit, and a rounded, open quarter to four inches long and a half to three- crown. There are several quarter-inch wide. The leaflets are oblong to species of mountain ash lanceolate, with serrated edges that go almost and mountain ashes, all the way to the base. They are dark green generally, are also known above and paler on the underside. In fall, as dogberry or rowan trees. leaves may turn red-orange to purple. American mountain ash is American mountain one of two species native to Twigs of American mountain ash are stout and ash leaves, Virginia gray to reddish brown and shiny.