By Michael Caduto
Consider the forest understory. One derivation of under implies a secondary position or role in relation to the trees that tower overhead, originating from the Old English for “beneath” or “underneath.” In other derivations, however, under means “between,” “among” or “in the presence of.” Indeed, when we walk through the lower, seemingly modest component of the forest ecosystem, where plants appear at a human scale, it is not immediately self-evident what a critical role the understory plays in sustaining the life cycle and health of a forest.
Just down the hall from Sustainable Woodstock’s office is that of the Hubbard Brook Research Foundation, a nonprofit organization that works to sustain and enhance the the Hubbard Brook Ecosystem Study. Since 1963, in their vast 7,800-acre tract of northern hardwood forest in New Hampshire’s White Mountain National Forest, Hubbard Brook has engaged in far-reaching, systematic studies of forest ecosystems. This research includes perhaps the most comprehensive long-term studies of plant species and their roles in the ecological dynamics of the forest understory.
From wildflowers, mosses and ferns to shrubs and young trees, the forest understory is often described as anything growing beneath the forest canopy up to 25 feet tall. But the forest understory is not just a community of plants that can tolerate heavy shade, it is the nursery for the trees that tower overhead. Without the understory, there would be no forest.
The forest understory also serves as critical habitat for many species, ranging from ladyslippers, witch hazel and skunk cabbage, to wood turtles, white-tailed deer and porcupines. Birds that spend much of their time feeding and nesting in the understory include the American Woodcock, Ruffed Grouse, Wild Turkey, Ovenbird, Scarlet Tanager and many of our woodland thrushes, including the Veery, Wood
Thrush and Hermit Thrush (Vermont’s State Bird).
Herbaceous plants and shrubs in the understory must tolerate heavy shade and intense competition for water and nutrients from the roots of trees in the overstory. Low-growing wildflowers need to also survive getting covered by leaf litter every autumn. When springtime arrives, they push up through the mat of leaves before the trees leaf out and while sunlight still bathes the forest floor. This survival strategy is responsible for the extravaganza of spring wildlflowers that carpets the northern hardwood forest, such as spring beauty, red trillium, bloodroot and trout lily. Common understory shrubs and trees range from low-bush blueberry and hobble bush, to witch hazel and striped maple. And, of course, all of our forest trees begin their lives as saplings growing in the understory nursery.
Many understory plants produce large seeds that can survive for years before the proper conditions arrive for germination. Others overwinter as perennial underground stems, bulbs, corms and rhizomes. Wild sarsaparilla, for example, spreads by rhizomes that form expansive patches which blanket the forest floor. Although this plant dies back to the soil surface every autumn, the rhizome can live for many years. As part of a botanical research project, I studied the rhizomes of wild sarsaparilla to count the annual rings of growth recorded there. Many of the rhizomes were more than 35 years old, a fact that is belied by the short plants that they produce each springtime which appear to the untrained eye like they have just sprouted from a seed.
Researchers with the Hubbard Brook Ecosystem Study have identified more than 400 species of plants growing in the northern forest, including 224 species of flowering plants, 150 mosses and liverworts, 26 kinds of ferns and their related plants and 6 species of conifer. Woody plants comprised 40 varieties of shrubs and 27 tree species, but more than 80% of the total number of forest species were herbaceous plants growing in the understory. These understory plants feed the soil and play a critical role in nutrient cycling. They shade the soil and so help it to retain moisture. Understory plant communities also provide life-sustaining food, shelter and nesting sites for wildlife.
Despite its resilience, the forest understory is a delicate ecosystem. The complex interconnections between species above ground and in the soil are easily disrupted or destroyed when clearing “brush” and when harvesting trees. Large clearcuttings have been found to eliminate many herbaceous species, decrease biodiversity and reduce regeneration of the forest. Dragging a log across the forest floor has been shown to sever the delicate threads (hyphae) of the symbiotic mycorrhizal fungi that are at the heart of a vast web of life that thrives in forest soils and makes possible life in the forest ecosystem.
As a naturalist, ecologist and observer of nature, in recent years I have noticed a significant increase of the destruction of forest understories. One recent trend: in the interest of opening up a view and creating a park-like setting in their woodlands, many private landowners are now mowing down and clearing the forest understory on a large scale around their homes. Not only does this destroy intricate plant communities that have taken decades to develop and evolve, it removes the nursery where the next generation of replacement trees for that forest would be nurtured. And as the plants go, so too do the food, shelter, nesting sites and cover for wildlife—including birds, mammals and insects. Clearing the forest understory creates an ecological desert where once there was a rich, diverse and thriving understory ecosystem. To destroy or degrade the forest understory is no less than killing the goose that laid the golden seedlings.
What can be done? Selective tree harvests that are part of a long-term forest management plan to preserve the health and diversity of the forest overstory, and that are conducted during winter when the ground is frozen, can minimize the impact on the forest understory.
And when it comes to managing the forest on your property, resist any temptation to clear the understory. Instead, focus on removing invasive species, encouraging native flora and enjoying the sights, sounds and presence of the rich variety of wildlife that frequent this diverse and dynamic environment.
Starflower and pink lady slipper are a small sample of the rich diversity of wildflowers that inhabit the forest understory. A clutch of eggs in an Ovenbird nest on the forest floor. (Photos by Michael J. Caduto)
WHAT YOU CAN DO:
- Contact your County Forester in order to connect with forest professionals who can provide advice and assitance on drafting and implementing an ecologically-balanced forest habitat management plan.
- Contact the Vermont Department of Forests, Parks and Recreation to inquire about cost-share and incentive programs for helping landowners accomplish conservation work on their land: fpr.vermont.gov