This specimen of eastern hemlock (Tsuga canadensis) was collected by former Carnegie Museum botany curator Sue Thompson on November 3, 1984 in Somerset County. Not only was this specimen collected in the highest point in Pennsylvania (Mt. Davis, 3,213 ft), but the species is also the official state tree of Pennsylvania. How’s that for your state trivia!?!
And this is a nice-looking specimen! Hemlock is a challenging species for the herbarium. It is notorious for shedding all of its needles when dried. Many specimens are just sticks with all the fallen needles shoved into an envelope.
Eastern hemlock (Tsuga canadensis) is a culturally and biologically important species. A keystone dominant species found across many eastern North American forests, hemlock serves as important habitat to many birds, among other species. Its leaves are evergreen and remarkable in casting some of the deepest shade, making the understory below it distinct. Many species are adapted to “hemlock-hardwood forests.” It provides food, shelter, and impacts nutrient and water cycles. It is a late successional tree, meaning its presence often indicates older, more intact forests.
Unfortunately, this species is in decline across its range, and it may become the “next American chestnut” so to speak. Hemlock is attacked by an introduced, invasive insect – the hemlock wooly adelgid (Adelges tsugae). The sap-sucking bug was accidentally introduced from its native East Asia, spreading to eastern hemlocks in the 1950s. First in the southern US, the impacts of the adelgid are clear in Great Smokey National Park, with hemlock stands wiped out and only the dead trunks and branches. The insect is fairly new to western Pennsylvania, only found in our region relatively recently and not yet fully spread. Check the undersides of hemlock needles for hemlock wooly adelgid. If the tree is infected, you’ll see their distinctive white cotton-like egg sacs.
As forest pests like the hemlock wooly adelgid spread and affect our forests, herbarium specimens are critical, serving as baseline data for species distributions and effects on other species through time and across sites.
Find this specimen of the state tree of Pennsylvania online here: http://midatlanticherbaria.org/portal/collections/individual/index.php?occid=11739325
Check back for more! Botanists at the Carnegie Museum of Natural History share digital specimens from the herbarium on dates they were collected. They are in the midst of a three-year project to digitize nearly 190,000 plant specimens collected in the region, making images and other data publicly available online. This effort is part of the Mid-Atlantic Megalopolis Project (mamdigitization.org), a network of thirteen herbaria spanning the densely populated urban corridor from Washington, D.C. to New York City to achieve a greater understanding of our urban areas, including the unique industrial and environmental history of the greater Pittsburgh region. This project is made possible by the National Science Foundation under grant no. 1801022.
Mason Heberling is Assistant Curator of Botany at the Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.