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Rock Creek Park's woods are beautiful whether or not you know one plant from another. Look more closely, though, and patterns appear: some plants are abundant on certain parts of the landscape and conspicuously missing from others, and some groups of plants turn up together again and again wherever the same conditions occur.
Natural communities
Those repeating groups of plants are called natural communities. Ecologists study and name them — the Chestnut Oak / Mountain Laurel Forest, for example, or the Red Maple Seepage Swamp. They are essential habitat for wildlife: some animals live in most communities, others in only one or a few.
Ecologists recognize eight natural communities along the trails of Rock Creek Park, some in the hills and some in the valleys.
When a place doesn't fit
What you see along a trail sometimes matches none of the mapped communities. Common reasons:
- Transitions (ecotones). Communities rarely have a sharp edge, whatever the map suggests. The zone between two mixes features of both, and hikers climbing up and down hills pass through such zones often.
- Semi-natural communities. Some areas are still regrowing from past disturbance such as farming, intense fire or unusually heavy storm damage.
- Mapping limits. Most maps leave out tiny patches of distinctive vegetation, say under 1 acre (1/2 hectare).
- Undiscovered communities. Now and then a new find leads ecologists to define a new community for a park.
Semi-natural communities: forests with a past
Rock Creek Park has many acres of semi-natural communities — vegetation growing where soil or plants were heavily disturbed by a severe natural event or by plowing, logging or quarrying. The vegetation is relatively young and is gradually giving way, or succeeding, to more natural communities. Wildlife turns over as it does: grassland birds in an abandoned field eventually give way to woodland birds as the field becomes forest.
Clues to the past. How a forest regrows depends on what happened to it:
- Logged with little ground disturbance: many original hardwoods come back from stump sprouts or saplings left behind, the forest floor may recover, and tree ages may vary. Look for old stumps, trees with several trunks from one stump, and deep holes where stumps rotted, sometimes ringed by the roots of neighbors.
- Burned intensely, plowed or bulldozed: with trees, stumps and the seed bank gone, an entirely new forest starts from pioneer species that sprout quickly on bare mineral soil — in the Mid-Atlantic, pine, tuliptree, sweetgum, black locust, red maple or sassafras. These tend to grow as even-aged stands of pine or tuliptree (or sweetgum on the Coastal Plain). As they die, the stand may slowly become the uneven-aged mix of a natural community, a process that can take centuries.
- Oaks as evidence: white oak and many other oaks are not usually in the canopy of a young forest on badly disturbed soil. Their acorns are slow to grow, and their saplings wait in the pioneers' shade, sometimes for years or decades, until a gap lets sunlight in.
Three of the park's semi-natural communities are recognized across the Mid-Atlantic and carry codes in the U.S. National Vegetation Classification (USNVC); the other four describe what occurs at Rock Creek Park but are not regionally recognized.
| Community | What it is |
|---|---|
| Successional Tuliptree Forest (Rich Type) (CEGL007220) | Towering, straight tuliptrees that look like an old natural forest but probably grew up after human disturbance — tuliptree seldom seeds into established forest and does best where disturbance exposes soil and opens the canopy. At Rock Creek it grows on moist, well-developed soils in areas that may have been cleared and farmed long ago, often upwards of a century ago, with a lush understory of northern spicebush and herbs and many invasive plants. American beech and oaks may eventually replace the tuliptrees, but some tuliptrees have reportedly lived 300+ years, so this could take a long time unless storms intervene. |
| Successional Tuliptree – Oak Forest (CEGL007221) | Tuliptree with similarly aged white and northern red oaks, small trees crowded together and a weedy understory, often dominated by invasive shrubs and plants. It occurs in small patches on land heavily disturbed — perhaps logged — but not plowed, and has few native shrubs; northern spicebush is uncommon. With age it becomes harder to tell from the Mesic Mixed Hardwood Forest. |
| Successional Virginia Pine Forest (CEGL002591) | Virginia pine needs bare mineral soil to establish and tolerates drier ground than tuliptree. Through the 1970s pines were frequent in the park's upland forests, perhaps in areas cleared for farms or for Civil War forts and sight-lines. Many have died; some remain near the Rock Creek Golf Course and Horse Center, and oak or beech usually replaces them. Virginia pines now appear mostly in the Coastal Plain Oak Forest of the Fort Circle Parks, or as remnants in other communities such as the Mixed Oak / Heath Forest between Bingham Drive and Wise Road. |
| Successional Mixed Deciduous Forest | Stands of varied age and makeup, mostly sun-loving, fast-growing "weedy" trees on disturbed ground — native black locust, tuliptree, elms, box-elder, poison ivy and cherries, with non-native Norway maple, honeysuckle, multiflora rose, English ivy and cherries. |
| Successional Vine-Shrubland | Dominated by invasive vines and shrubs; any native trees may be sparse and choked by vines. |
| Planted Evergreen Forest | Areas where evergreens appear to have been planted; the evidence may be more or less obscured depending on how long ago they were planted and last thinned. |
| Historic Quarry | Former quarry ground dominated by hardy, fast-growing invasive trees, vines, shrubs and small plants, with few natives. |
Dumbarton Oaks Park: escaped art
Dumbarton Oaks Park was once part of the carefully planned gardens of an estate in north Georgetown, Washington, D.C. In 1940 the owners, Ambassador Robert and Mildred Woods Bliss, gave the formal gardens and hilltop mansion to Harvard University and the lower, more naturalistic 27 acres to the U.S. government as a public park; it is now a unit of Rock Creek Park.
The grounds were meant to look like natural woodland, but the original design planted non-native vines such as Japanese honeysuckle and periwinkle, some of which became aggressive invaders, and ornamental plants from the formal gardens uphill seeded themselves into the stream valley. By the beginning of the 21st century, porcelain-berry, bush honeysuckle, English ivy and other invaders threatened its meadows and woods. Volunteers working with the National Park Service and others began restoring it, through a plan that started when the Dumbarton Oaks Park Conservancy formed in 2010.
Not-so-natural communities
Lawns, golf courses and maintained meadows are neither natural nor semi-natural. This managed, "cultural" vegetation includes:
- Maintained meadows — about a dozen or more small openings mowed occasionally for wildlife such as field mice and their predators, butterflies, pollinators and grassland birds. Lightning fires and fires set by Native Americans may once have created occasional prairie-like openings here.
- Picnic areas near the creek, where the trees are typical floodplain species but the understory is mowed lawn.
- The Rock Creek Golf Course, other regularly mowed areas, and plantings around buildings.
- Stormwater retention ponds — human-made, cattail-filled wetland swales northeast of the core park, in the Fort Circle Parks, built to slow and filter urban runoff before it reaches streams.
Ecological systems
Natural communities that tend to occur together and share natural processes, such as flooding or fire, form ecological systems; a River Floodplain Ecological System, for example, groups the communities found on floodplains. Rock Creek Park's natural communities belong to four.
Picture a long, high ridge: one ridgetop community may be almost all chestnut oak, another a wider mix of oaks and shrubs, but all share dry soil, exposure to sun, wind and storms, and lightning fires. Or picture a large river, with sycamore and tuliptree forest, shrubby willows and a mucky alder swamp, all shaped by the same floods. Knowing the system helps predict what will thrive: no one expects a flood-adapted community on a dry ridgetop, or a fire-adapted one on a riverbank.
Sources
- National Park Service: "Rock Creek Park Natural Communities and More," part of the series Rock Creek Park Ecology.
- References it cites: Fleming (2007), personal communication on Rock Creek Park's vegetation; Anderson and others (1977), on the vegetation communities of Rock Creek Park and the Rock Creek and Potomac Parkway; Joseph, Fanning and Davison (2000), Cultural Landscape Report: Dumbarton Oaks Park; The Cultural Landscape Foundation (2006).
- The source's list of the park's eight natural communities did not come through in the copy used here.
Dans ces publicationsRock Creek Park
Licence : CC0 1.0 (domaine public) · Adapté de www.nps.gov
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