by Carl R. Gold
According to Dr. Nancy Sonti, a Research Ecologist with the US Forest Service, growing a forest is “both an art and a science.” The art part is comforting news to your author, whose worst grade in college was in “baby” biology. The science, however, is crucial. Trying to ensure the survival of an urban forest, i.e., to regenerate it, is referred to as urban silviculture. Fortunately, the Forest Service, a branch of the U.S. Department of Agriculture, has assigned some smart people to help. Dr. Sonti is one of them. She recently led a walk and talk at Cylburn Arboretum in Baltimore City, just downwind of Pimlico racetrack. Cylburn is one of two sites in Baltimore City being used for the regenerative study.
Forests are managed, grown, or regenerated for many reasons: timber, watershed preservation, erosion control, carbon sequestration, wildlife habitat, and biodiversity. Absent assault, in an unfettered state of nature, forests regenerate themselves. Unfortunately, assaults come in many forms. Urban forests face not only encroachment from development, waste water, storm water and impervious surface runoff, pollution, high temperatures, drought, and limited space, but also some of the same challenges suburban and rural forests face, namely deer pressure and nonnative invasive species.
Municipal forestry services with strained budgets often focus solely on single street trees or horticultural, i.e., landscaped areas. While these are worthy endeavors, this concentration leaves pockets of forested land to fend for themselves. Nonnative species prevalent in the Baltimore Metropolitan area include oriental bittersweet, Japanese stilt grass, multiflora rose, porcelain berry vine, English Ivy, and Japanese barberry. They thrive because they have no predators; not even deer will eat them. They crowd out spring ephemerals and other native plants, including native tree seedlings. Deer feasting on native species such as young tree saplings cause additional pressure. This combination creates a crescendo of problems. A forest cannot regenerate itself if all the young seedlings are eaten or subsumed by nonnative species.
The Native Oak Regeneration study spans the eastern seaboard from Massachusetts to Maryland, with test sites in Springfield, Mass., New Haven, Conn., Philadelphia, PA., and Baltimore City, Md. The Forest Service chose oaks for the study due to their crucial place in ecosystems. University of Delaware Professor and leading native plant advocate Doug Tallamy has shown that one mature oak tree can host over 500 species of insects: food for our feathered friends. The acorns a mature oak produces feed a diverse group of wildlife. Study participants collected over a hundred thousand acorns from white oak and chestnut oak trees in the test areas and more southern locations in Kentucky and Tennessee. They were sent to Dr. Laura DeWald, a researcher at the University of Kentucky specializing in oak tree genetics. Once the acorns became saplings, a process that took a year, the Forest Service planted them at the four carefully-chosen test sites. They excluded highly degraded forest areas–those overrun with nonnative invasives or subject to uncontrollable deer pressure– due to the low likelihood of survival. Instead, they selected “good woods”– not problem-free, but with the following characteristics:
• Some areas of open canopy so that enough light can reach the saplings
• A manageable number of nonnative understory plants that can be removed and controlled
• An area that allows fencing to exclude deer
• Accessible enough to allow monitoring
Cylburn Arboretum and Leakin Park, both in Baltimore City, each contain test areas. The Forest Service and volunteers removed nonnative invasives and fenced the test sites, leaving existing native trees and vegetation undisturbed. Year-old saplings were planted in the Spring of 2023 at the rate of 100 to 200 seedlings per acre.
The Cylburn study areas are reachable after a short hike. (The Vollmer Center has directions.) Each sapling is marked with a colored flag delineating whether it is a chestnut or white oak. Depending on the site, the saplings are planted 4 feet or 8 feet on center. At Cylburn, the 4-foot-centered trees are in the midst of an established forest with a partial canopy opening created by felling a dead tree. The 8-foot-centered saplings are in an “oak orchard” next to an access road with no canopy and therefore no shade. The presumption is that the trees in the completely open area will grow faster and therefore need more room. Dr. Sonti also expects a higher mortality rate in the canopy gaps so ‘it’s ok to have them planted closer together.”
The scientists will measure the impact, if any, of seed source on tree performance and forest ecology by examining morphology, root structure (including root collar diameter), leaf production and photosynthesis rates and considering the impact of light and moisture. Since the saplings are protected from their two major predators, they hope that the study areas will regenerate. Forest ecologists realize that this study will take decades; oaks are slow growers that will outlive all of us. If successful, hopefully experts can develop a blueprint to expand regenerative areas and city planners can be convinced to direct resources to support this expansion. Even though a forest may look “good” or even healthy now, if its progeny are not allowed to survive and thrive, future generations will suffer. As Kim Pause Tucker, executive director of the Gunpowder Valley Conservancy, puts it, “humans are not separate from the environment.”
Carl R. Gold is a Maryland Master Naturalist and can be reached at cgold@carlgoldlaw.com, Twitter and Instagram @crgkoko.
