G - General Plant Communities

A plant community, as defined by Fike (1999) is “an assemblage of plant populations sharing a common environment and interacting with each other, with animal populations, and with the physical environment.” These interactions occur at a wide range of scales, from those involving regional factors such as climate and geology, to those involving chemical reactions and soil microbes. With so many (and often conflicting) influences, plant communities, especially in this area, are not discrete, easily-classified units but better placed on a continuum. In addition, the speed and magnitude of human- (and deer-) caused alterations of the environment appear to have degraded native plant communities faster than they can adjust, and as a result many currently wide-spread plant communities have become dominated by aliens, especially below the forest canopy. Plant communities in this area can only be broadly delineated according to available moisture and dominant species.

Forests, or older woodlands, have a closed canopy of trees older than 60-70 years in age. They range from dry chestnut oak-heath, to oak mix, to moister (i.e., mesic) combinations of oaks, beech, hickory ash, and tulip, to swamp forest dominated by red maple, pin oak, and black gum. Swamp forests are uncommon in the Township, with perhaps the best example in the Cockeysville corridor (ENA 4). Chestnut oak-heath communities are found on drier ridges, and like swamp forests only a few fragments remain. The best examples of this community grow at the airport and along the White Clay Creek; these have been identified as “Exceptional Natural Areas” (ENAs). Specifically, these examples are labeled as ENA 9 and ENA 11, respectively. ENAs are described starting on p. 17, while they are shown on Maps 3 and 4. 

Oak-mix forests are widespread, as are more mesic beech-tulip-hickory-oak or tulip tulip-ash forests. Often larger wooded areas are patchy with oaks and hickories more common on thinner, eroded slopes and beech and tulip dominant on richer deeper soils on lower slopes. Older beech and younger tulip indicate past logging, generally for oak. Beech is intolerant of fire, and may be absent because of repeated burning. Beech-dominated forests generally have little undergrowth; exceptions usually have a dense sapling layer of beech. Tulip-oak or tulip-dominated forests are richer in both shrub and herb diversity and quantity, but are also more likely to have considerable amounts of multiflora rose, garlic mustard, and other invasives, and spicebush is usually the only significant native shrub. The quantity and quality of native herbaceous species can vary considerably in these woodlands, depending on canopy dominants, past use, deer pressure, and alien load. Better quality mixed forests are found in ENAs 5, 6, 7, 11, 12, and 14. 

Floodplain hardwood forests on alluvial soil are usually in small groves or fragments surrounded by younger woodlands with a walnut, ash, and /or box elder maple canopy over impenetrable thickets of multiflora rose and alien herbs and grasses. Older sycamore, silver maple, bitternut hickory, and pin oak sometimes line the stream edge. The White Clay north of Landenberg has some patches of floodplain forest, mostly surrounded by younger low-quality maple- rose woodland. Typical floodplain herbs such as Jacob‘s-ladder, Virginia waterleaf, zig-zag goldenrod, and some sedges and grasses are uncommon and losing ground to the highly invasive lesser celandine. ENAs 10 and 11 have patches of floodplain hardwood forest. 

Younger woodlands often have a closed or nearly closed canopy similar to forests, but tend to be dominated by one or two species of native mostly early successional trees, usually tulip, ash, red maple, black walnut, and black cherry. They rarely have a well-defined understory. Aliens frequently dominate the shrub and herb layers. Common shrubs include autumn olive, multiflora rose, spicebush, black-haw, and brambles (Rubus spp.). Vines such as Japanese honeysuckle, bittersweet, grape, poison ivy, and Virginia creeper are generally abundant, both along the ground and climbing up trees along edges or in gaps where there is more light. Garlic mustard, stilt-grass, violets, and white avens are typical common herbs growing in this habitat. A common subcommunity on low ground and abandoned pastures is young walnut-dominated woodland with an open canopy and a thick alien shrub-vine-herb layer. Most young woodlands have some native shrubs and herbs present, although isolated blocks often entirely lack them. Today it is an unusual young woodland that has more natives than aliens below its canopy and/or a significant amount of oaks and hickories in the canopy; none were observed in New Garden. 

Wetlands. Natural wetlands in New Garden mostly occur along stream corridors, as seepage springs or wetlands or at the base of slopes, in old stream channels or overflow channels, along streams, or poorly drained areas near and on stream drainage divides. Wetlands on Cockeysville marble may be the result of old sinkholes or inhomogeneity in the underlying bedrock. Man-made wetlands occur below ponds, in storm water detention basins, or where natural drainage has been impeded by roads or railroad beds. 

Small wetlands in woods are usually marked in early spring by the appearance of skunk cabbage, with violets, jewelweed, and tearthumbs appearing and flowering later in the season. Other typical woodland seep species include golden saxifrage, rough bluegrass, Pennsylvania bittercress, and certain sedges. Spicebush, arrowwood viburnum, elderberry, and winterberry are common shrubs; red maple (occasionally accompanied by black ash) is the typical shade tree if the wetland is large enough to influence the canopy. 

Common marsh or open wetland plants include sensitive fern, jewelweed, tearthumbs, soft rush, purple-stemmed aster, goldenrods, rice cut-grass, reed-canary grass, and numerous sedges. Cattails and arrowhead generally grow only in the wettest areas where the ground is almost permanently inundated. Shrubs and trees such as black alder, swamp rose, buttonbush, red maple, and green ash begin the succession of a marsh to a swamp. The European strain of reed-canary grass is one of the biggest threats to wetlands, commonly taking over marshes and open stream corridors, especially where there has been disturbance and increased nutrient and sediment inflow (which is everywhere in the Township). Phragmites is also common, while purple loosestrife is frequent, though not as aggressive. A variety of types of wetlands are found in ENAs: an open small stream wetland in ENA 1, wetlands on Cockeysville marble in ENA 3 and 4, a sandy acid seep in ENA6, a partly man-made open wetland in ENA 9, swampy woods with an old slough in ENA 10, hillside rocky seeps in ENA 11, and a pond edge marsh in ENA 14. 

There are several created wetlands in the Township that would be considered successful restorations in that they seem to have formed stable plant communities with a fair diversity of non-invasive wetland species. However, they stand out from natural wetlands because they generally contain species that would not normally be expected in southern Chester County. A number of the species listed as ‘Introduced’ occur in these restorations. 

Aquatic habitats include streams and ponds. Duckweed (Lemna minor) is the most common floating aquatic, found in both streams and ponds, sometimes with water meal or greater duckweed. Only some of the Township‘s numerous ponds were visited during this survey, so the frequency of aquatic plants is likely underrepresented in the plant list; also, of the ponds that were visited, many were steep-sided or groomed to water‘s-edge and so may well have lacked a diverse flora. The alien water-starwort (Callitriche stagnalis) occasionally grows in mats along the edges of streams where there is a silty or muddy substrate. Much of the White Clay Creek is too shady for a diverse aquatic or stream edge community, but a small pond at Somerset Lake had some horned pondweed (Zannichellia palustris) which has been seen downstream on the White Clay and possibly occurs elsewhere in the Township in similar habitat. A shallow pond in Candlewyck along Sharp Road had little truly aquatic vegetation, but did possess a textbook example of a drawdown shoreline habitat. 

Transitional habitats (edges, hedgerows, thickets, old fields). These habitats have high light levels and are generally dominated by woody species with mobile seeds that are spread by wind, birds, or mammals. Common trees along edges and hedgerows include black cherry, ash, sassafras, red maple, and walnut. They shade a mostly alien-dominated mixture of shrubs including multiflora rose, Amur honeysuckle, spicebush, black haw, crabapple, and brambles. Old hedgerows of Osage orange are the cores of many hedgerows, especially along old farm lanes. Most hedgerows and woodland edges are knit together by a mostly woody suite of vines such as bittersweet, Japanese honeysuckle, poison ivy, grapes, Virginia creeper, and recently, mile-a-minute and porcelain-berry. The ground flora is generally low in diversity and dominated by aliens. White avens, garlic mustard, field garlic, and stilt-grass are some of the common ground species. 

Old fields, or early successional habitats such as abandoned cropfields and pastures, are transitional and ephemeral in nature. As time passes after abandonment, these habitats soon progress from annual herbs or pasture grasses to perennials such as goldenrods, asters, and broomsedge. In this area they are quickly invaded by woody aliens such as multiflora rose, autumn olive, bittersweet, and Japanese honeysuckle, with natives such as poison ivy, grapes, and tree saplings contributing heavily. 

Thickets are old fields where the shrubbery, vines, and tree saplings (especially red maple, black cherry, ash, and tulip) have grown tall or dense enough to form a low but closed canopy. The boundary between old field and thicket is not always clear, and the two habitats often interfinger until the patches of closed canopy merge. Old fields, thickets, and edges once supported a diverse mix of native grasses, sedges, asters, goldenrods, tick trefoils, clubmosses, and shrubs. Today the majority of these habitats, especially along cropfields and in lowlands, contain a limited number of hardy natives with the aggressive aliens. 

Successional habitats rich in native species have become rare, but occasionally under unusual circumstances they do appear and persist; two good examples exist in New Garden. Because of its Cockeysville substrate (and probably past disturbance), an old field west of Church Road (ENA 8) has seven species seen nowhere else in the Township that are also uncommon in the area. The poor soil over Setters quartzite and infrequent mowing of a steep bank at the airport (ENA 9) has suppressed invasives and allowed a number of dry edge species, including a number of state and local rarities, to thrive.

Open Lands (meadows, fields, heavily managed communities, and roadsides). Since any ground left alone in the region is soon colonized by woody vegetation, all non-wetland areas dominated by herbaceous plants are managed to some extent. 

Meadows are areas defined as open ground that is not a wetland and where the majority of the flora is composed of native forbs, grasses, and sedges; drainage, soil type, and slope determining the species present. Common wet meadow species include wide variety of sedges along with rushes, joe pye-weed, goldenrods, ironweed, swamp milkweed, and agrimony; the vegetation in less-managed areas frequently grows lush and tall. Drier or lower- and mid-slope meadows, whose vegetation is generally shorter in stature, are commonly dominated by goldenrods, asters, grasses (including fescue, purple top, sweet vernal grass, broomsedge, Indian grass), and sedges, mixed with broader-leaved herbs such as dogbane and milkweed. The driest meadows, on upper slopes or hilltops, are generally dominated by warm-season grasses such as broomsedge and little bluestem, mixed with shorter grasses like panic-grasses and are accompanied by low-growing herbs including dwarf cinquefoil, hawkweeds, ox-eye daisy, tick-trefoils, grey goldenrod, uncommon milkweeds, and hardy sedges. Creepers, especially dewberry, frequently invade this habitat, especially near edges. Patches of bare ground, often the result of mowing practices or less often foot trails, are home to annuals including three-seeded mercury, sheep sorrel, and milkwort. Drier and wetter portions of meadows and stretches along woodland margins tend to have the greatest diversity of species; in general, the older the meadow, the higher native plant richness it possesses.

Unmown meadows are soon invaded by poison ivy, honeysuckle, multiflora rose, and tree and shrub seedlings. However, too-frequent mowing discourages native herbs and grasses and turns a meadow into a Field, or an open area dominated by alien pasture or hay grasses such as orchard grass, fescue, bromes, bluegrass, and timothy; all mixed with mostly alien broad-leaved herbs including clover and thistle. Most fields, even the most heavily utilized or managed, usually possess a few native species, especially along edges, moister areas, or on steep slopes, and the distinction between a meadow and a field is often unclear. 

Large areas of high-quality meadow are uncommon in the region, and the best meadows in the Township are mostly small patches that merge into a larger field. The airport (ENA 9) has a meadow complex in the southeast that transitions from dry slope to wet bottom in a short distance. The Cockeysville corridor has several low meadows surrounded by low-diversity fields (ENA 3, 4), and there is a small roadside meadow along Hillendale Road (ENA 2). 

Utility Corridors. By law and necessity, rights-of-way must be kept clear; accordingly, those portions of the corridor not actively farmed nor kept as lawn are kept in a permanent state of early succession. Although too often this continually disturbed condition favors the explosive growth of alien invasives and hardy natives, occasionally native-dominated communities develop or persist, especially in dry exposed areas or wetlands. The largest right-of-way in the Township is for the Colonial Pipeline, which cuts across the south end of the Township near Somerset Lake. However it was cleared just prior to the survey, making it difficult to assess the condition of any native communities present.

Sand and gravel bars are the only open habitats in the Township currently managed and perpetuated by ‘natural’ means; i.e., flooding and fluctuating water levels. Their substrate varies from coarse cobbles to mud, and if they occur in sunny areas and are not overrun by hops or reed-canary grass, these sites can harbor a surprisingly large number of disturbance-tolerant species (both native and alien) in a small area. Most of the gravel bars on the White Clay are too shady and too coarse in texture to develop much of a gravel bar assemblage. The sand bar-delta at the mouth of Somerset Lake (ENA 12) had a well-developed mix of sedges, grasses, smartweeds, and other herbs. Since the diversity of this habitat depends on the water level, it varies considerably from year to year.

Heavily managed or ruderal communities include pastures, active cropland, lawns, roadsides, and golf courses. In additional to cultivated species, each of these continually disturbed habitats possess a typical suite of weedy, mostly alien, and annual species including clovers, plantains, chickweed, lamb’s-quarters, ragweed, thistles, and various grasses. These habitats, characterized by unstructured, low-diversity plant assemblages and compacted and chemically altered soils, allow rapid runoff of rain and nutrients (including organic and inorganic fertilizer), degrading stream and groundwater quality. 

Roadsides, especially in sunny areas, are typically dominated by a few hardy and adaptable species including knotweed, plantains, ragweed, brome-grass, and chicory, which are able to tolerate the harsh environment of temperature and moisture extremes, excessive mowing, pollution, and poisoning. Nonetheless, roadsides often possess a surprising diversity of species, both native and alien, just a few feet back from the pavement, especially in undeveloped areas. The richness of a roadside, especially in native species, can be an indicator of the relative health of a neighboring plant community, be it open or wooded. Since wooded roadbanks tend to be avoided by deer, they can also be higher-quality refuges along the edges of older but degraded woods.