How hemlock holds a forest together

An evergreen plant of the week and an essay by Major Jackson

Plant of the week: Eastern hemlock

In this rudderless time, I’m drawn to a foundational species of tree, eastern hemlock (Tsuga canadensis.)

One scientist notes that the tree’s transformative effects on a forest “are recognized not only by ecologists but also by poets, writers, naturalists, and many other nonscientists.” I think this is largely attributable to the brightness of a hemlock stand in winter, which I encountered on a walk around one of Greater Boston’s many kettle ponds that goes by the name of Walden. Having passed through oak and maple trees in drab colors, we reached a cove where hemlock needles sparkled in the sun. The change is like flipping on a switch. Pine, though green all year, mostly has leaves high up in a mature forest, not down at human eye level, and doesn’t have the same effect. Hemlock surrounds a person with green—above, below, brushing hands and face.

The enveloping presence of hemlock called to mind a vague sense of its importance in ecosystems — I couldn’t remember specifics besides something about nutrient cycling. When I began digging into the topic, I soon realized that hemlock’s presence or absence affects almost every part of the ecosystem. Some researchers argue that it’s a “foundational species,” because the species so completely alters and regulates the ecological community around it.

The first part to mention is what hemlock does with water. Photosynthesizing all year, and with shade-tolerant needles at all levels of the canopy, it pulls a tremendous amount of water out of the ground and pushes it out through its leaves — so much so that a loss of hemlocks along a stream can lead to greater water discharges, wider stream beds, increased erosion — a whole cascade of negative effects. The release of water through hemlock needles, along with the dense shade created by its branches, is enough to change the microclimate. Hemlock stands hold moist air that moderates the temperature: cool during the day and warm at night. Meanwhile, the soil remains dry (because of the roots draining the water like a shop vac) and cool (because of the shade from the canopy.)

All these structural and environmental effects make hemlock forests a place where amphibians such as newts and salamanders can live. That’s significant, because amphibians have lost much of their habitat to wetland drainage and development. Birds with specialized habitat needs such as certain warblers and flycatchers also are more abundant in intact hemlock forests. Take the hemlocks out, and you get an early-successional forest with abundant spiders, ants and predatory beetles — nothing against these species, but there’s plenty of other places they can live.

Eastern hemlock is limited to the Appalachian Mountains in the South, much of New England, and the upper Great Lakes. Unfortunately, it has a mortal threat: the hemlock woody adelgid, an aphid-like insect that feeds on sap. The insect has a tight relationship with warming climates: first introduced in Virginia, it has spread northward and upward in elevation as winter temperatures have declined. The only thing that can really stop adelgids are winter temperatures below -13 degrees F, something that just doesn’t happen very often anymore, even in the Northeast.

The hemlocks you might once have seen in the woods were enormous. I have only seen medium and small ones. Still, young hemlocks are a small sign that the species isn’t beaten yet, that it’s still propagating and transforming forests despite the threats against it.

Major Jackson on the death of Joseph Lee Wood

The poet Major Jackson recently wrote a moving, challenging essay reflecting on the death of Joseph Lee Wood, a Black writer who vanished on Mt. Rainier in 1999. “Joe’s intolerance for vapid ideologies pushed him as a writer to avoid facile conclusions and to seek topics for his writings that led to complex arguments about identity and society,” Jackson writes. “In a Yeatsian sense, Joe quarreled with both himself and the world.” I think those sentences also work as a description of this essay. Jackson succeeds creating a nuanced remembrance of Wood and what his death has meant to Jackson and others over the years — most recently in the wake of police murders of Black people in 2019. Jackson considers what it means to go out into the Green Mountains or Mt. Rainier as a lone Black man or with his wife, despite being an experienced hiker and naturalist.

The more Jackson has thought about it, the more he suspects Wood was murdered. “What else could explain the disappearance of a Black man on a warm, cloudless day in July?” he writes. The essay is less an attempt to pin down what happened and more of an examination of storytelling about the death, and Jackson’s own attempt to assemble a clear narrative about what the tragedy means. On a daily level, it means that, “unlike my fellow trail walkers or bikers or kayakers, I never fully enjoy nature outings because of the persistent fact of the precariousness of Black life,” Jackson writes. The place Jackson concludes doesn’t leave the reader comfortable — and it shouldn’t, particularly for white readers like me. The essay instead reflects on the bravery and power contained in a Black person’s decision to go into the woods, into the world in general.

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Possum Notes is a weekly newsletter about wildlife and landscapes around where I live. It’s produced on occupied Massachusett and Wampanoag land.