Throughout the eastern United States, one of our most iconic forest trees is dying. Eastern hemlock (a.k.a. Tsuga canadensis; Figure 1) is being sucked to death by a small insect, the hemlock woolly adelgid (a.k.a. Adelges tsugae). As a scientist, I study how our forests may respond to the loss of this “foundation” tree species.[i] As a human being, I cry, I mourn, and I look to the future for hope.
To reconcile the desire for knowledge and the emotional tearing that affects many of us who study eastern hemlock and all of us who are living with these fading trees,[ii] I have partnered with two artists—David Buckley Borden and Salua Rivero—to develop Hemlock Hospice: a collaborative, field-based installation that blends science, art, and design that  respects eastern hemlock and its ecological role as a foundation forest species;  promotes an understanding of the adelgid; and  encourages empathetic conversations among all the sustainers of and caregivers for our forests—ecologists and artists, foresters and journalists, naturalists and citizens—while fostering social cohesion around ecological issues.
Starting today, and over the next several weeks, we’ll be installing Hemlock Hospice in and around the oldest stand of eastern hemlocks in the Prospect Hill Tract at Harvard Forest, and I’m using this space to keep track of its background and progress. I’ll also be presenting an overview of Hemlock Hospice in a five-minute “ignite” talk at the Annual Meeting of the Ecological Society of America in Portland Oregon, August 6-11, 2017.[iii]
What is an eastern hemlock, and why do so many scientists and poets care about it?
Not to be confused with Socrates’ hemlock,[iv] eastern hemlock is a long-lived, cone-bearing tree[v] that grows from Georgia in the southeastern United States, northward into eastern Canada, and west into Ontario, Michigan, and Wisconsin (Figure 2).
Eastern hemlock is what ecologists call a foundation species. Its unique biophysical and biological characteristics lead to it controlling the diversity and abundance of other, oft-times unique, species that live in eastern hemlock forests and to regulating and modulating the cycling of energy and nutrients through the forest. Without eastern hemlocks, we wouldn’t have “hemlock forests,” which stands in contrast with, say, maples (Acer spp.), which normaly grow together with many other tree species in “mixed deciduous forests.”[vi]
Scientists care a lot about the decline of eastern hemlocks because a forest without a foundation is a lot like a house without a foundation—in either case, the structure collapses. Those species that depend on eastern hemlock will disappear as their home disintegrates. Cycling of energy and nutrients will change from what they have been for hundreds or thousands of years into…well, something else. Furthermore, eastern hemlocks often grow along streams and small rivers, where the ability of these evergreen trees to photosynthesize year-round leads them to even out the normal seasonal variations in stream-flow; the loss of hemlock is likely to lead to more flash-floods.[vii]
Unlike other species of trees in the eastern US that have been or are being threatened by insects and pathogens—a few examples among many, many others include American chestnut, American elm, and White Ash[viii]—hemlock is not especially economically valuable. Although its bark was once the staple input for the tanning industry, the invention of synthetic tannin removed the last real economic incentive for harvesting eastern hemlock. In fact, what little remaining old-growth forest there is in the eastern US is mostly small patches of eastern hemlock trees > 300 years old that were ignored by people seeking valuable timber.[ix] Thus, eastern hemlock may yet escape the fate of chestnut and elm, which, in the face of chestnut blight and Dutch elm disease in the early- and mid-twentieth century, respectively, were harvested rapaciously without regard for the possibility that resistance could evolve.
At the same time, many of these trees are dying, and, like chestnut blight and Dutch elm disease, the hemlock woolly adelgid is difficult to control. We can’t build walls to keep the adelgid out and we can’t inject insecticides into every one of the seemingly innumerable trees in a forest. But we can stop to think, reflect, and plan for a future with little or no eastern hemlock.
Welcome to Hemlock Hospice. Follow along and join the conversation.
[i] For reviews, see A.M. Ellison et al. 2005. Frontiers in Ecology and the Environment 3: 479-486 (doi: 10.1890/1540-9295(2005)003[0479:LOFSCF]2.0.CO;2); A.M. Ellison 2014. Advances in Ecology 2014: article 456904 (doi: 10.1155/2014/456904)
[ii] A readable scientific and cultural introduction about hemlock past, present, and future is D.R. Foster, editor 2014. Hemlock: A Forest Giant on the Edge. Yale University Press, New Haven, Connecticut, USA.
[iv] The hemlock that killed Socrates is Conium maculatum, a 1- >2-m tall biennial herb in the Apiaceae family of flowering plants. Like other Apiaceae, including carrots, celery, and parsley, Conium maculatum has a head of small white flowers perched atop its green, non-woody stem. The original range of Conium maculatum includes temperate regions of Europe, West Asia, and North Africa; it is now established and naturalized throughout Asia, North America, Australia, and New Zealand. Its toxic effects on animals result from a variety of alkaloids that disrupt the central nervous system. The description of the death of Socrates (399 B.C.E.) following his conviction for impiety and corruption of young men is consistent with acute poisoning by Conium. Conium maculatum favors moist soils, but it also may grow on roadsides, in ditches, and in vacant lots.
[v] Conifers like eastern hemlock (Tsuga canadensis) are in the plant division Pinophyta (conifers). Flowering plants like Conium maculatum are in the Angiosperms (Eudicots: Asterids: Apiales). Socrate’s poison hemlock and the coniferous eastern hemlock are about as closely related to each other as humans are to starfish.
[vi] Unless they are planted in sugarbushes for maple syrup production.
[vii] See C.R.Ford & J. M. Vose. 2007. Tsuga canadensis (L.) Carr. mortality will impact hydrologic processes in southern Appalachian forest ecosystems. Ecological Applications 17: 1156-1167. [pdf – external link]
[viii] For a recent review, see G. M. Lovett et al. 2016. Nonnative forest insects and pathogens in the United States: impacts and policy options. Ecological Applications 26: 1437-1455. [pdf – external link]. Associated non-technical discussion here: [external link]
[ix] See, for example, A.W. D’Amato, D.A. Orwig, & D.R. Foster. 2006. New estimates of Massachusetts old-growth forests: useful data for regional conservation and forest reserve planning. Northeastern Naturalist 13: 495-506. [pdf – external link]