Physiognomy and Structure: The vegetation is dominated by forbs, grasses, ferns and shrubs. Tree saplings may form a growing percentage of the cover should succession lead to a forested state.

Floristics: There are three variants of this vegetation, each of which has its own characteristic herbs and shrubs. The better known variants are the "mesic open old-field meadow variant" and the "mesic old-field shrubland variant." There are also dry variants which are less well-described. The mesic old-field meadow variant is dominated by forbs and grasses that occur on sites that have been cleared and plowed (for farming or development), and then abandoned. These characteristic forbs include Asclepias syriaca, Centaurea stoebe ssp. micranthos (= Centaurea maculosa), Cerastium arvense, Daucus carota, Euthamia graminifolia, Fragaria virginiana, Oenothera biennis, Picris hieracioides, Potentilla simplex, Rudbeckia hirta, Solidago altissima, Solidago canadensis, Solidago juncea, Solidago nemoralis, Solidago rugosa, Symphyotrichum lateriflorum (= Aster lateriflorus), and Symphyotrichum novae-angliae (= Aster novae-angliae). Common invasive and exotic grasses include Anthoxanthum odoratum, Bromus inermis, Dactylis glomerata, Elymus repens (= Agropyron repens), Phleum pratense, Poa compressa, and Poa pratensis. Shrubs may be present, but collectively they have less than 25% cover. Characteristic shrubs in this variant include Cornus amomum, Cornus racemosa (= Cornus foemina ssp. racemosa, = Swida racemosa), Cornus sericea (= Swida sericea), Juniperus virginiana, Rhus typhina, Rhus glabra, Rubus spp., and Viburnum recognitum (= Viburnum dentatum var. lucidum) (Edinger et al. 2002). The mesic old-field shrubland variant occurs on sites that have been cleared (for farming, logging, development, etc.) or otherwise disturbed, and has at least 25% cover of shrubs. Its stands are typically dominated by Amelanchier spp., Cornus racemosa, Cornus sericea, Crataegus spp., Juniperus virginiana, Pinus strobus, Prunus virginiana, Prunus americana, Rhus glabra, Rhus typhina, Rubus spp., Viburnum lentago, and Viburnum recognitum. The exotic shrubs Elaeagnus angustifolia, Lonicera spp., Rhamnus cathartica, and Rosa multiflora may be invasive in some areas (Edinger et al. 2002). The dry old-field grassland and shrubland variant is found on sandy or rocky substrates and is typically dominated by Andropogon virginicus, Poa compressa, Schizachyrium scoparium, Solidago nemoralis, and an assortment of dry weedy species such as the exotic Centaurea stoebe ssp. micranthos. A north-south gradient in floristics occurs, including in the herbaceous layer, where old fields in the north are more strongly dominated by Solidago spp. and those in the south by bunchgrasses (especially Andropogon virginicus, Schizachyrium scoparium, and Andropogon gerardii) (Wright and Fridley 2010). Changes in shrub and tree species from south to north are also noteworthy.

Dynamics:  Depending on the availability of adjacent seed sources, ongoing mowing, etc., sites may either remain as herb- and shrub-dominated meadows for 20-50+ years, or may succeed to forests. Sites in which Rhamnus cathartica establishes may persist in a small-tree state for many years. A wide variety of studies have been completed on old field dynamics in this region (e.g., Egler 1954, Bazzaz 1968, Myster and Pickett 1990, Gill and Marks 1991). For a recent synthesis of these studies in this region, see Wright and Fridley (2010). For a list of trees that establish on old fields, see Wright and Fridley (2010, Table 1). See also Motzkin and Foster (2002) for a discussion of old ruderal sandplain sites with a mix of natural and novel characteristics. Examples of these fairly natural sandplain associations include ~Vaccinium angustifolium / Schizachyrium scoparium - Carex lucorum Shrub Grassland (CEGL006393)$$.

It is possible that the successional sequence may lead to a recognizable, if simplified, native forest type in this region. Further review of the literature is needed. See Sivicek and Taft (2011) for a comparison of assisted succession in tallgrass prairie that leads to a recognizable, though lower quality, native grassland type. Similarly some natural types that originate through both natural and human disturbances have natural analogs and are placed in other "natural" groups. A well-studied example is the "old field" sand barrens of the upper Midwest, studied at Cedar Creek Natural History Area (Inouye et al. 1987). They are treated as "native successional grasslands" within ~Central Tallgrass Prairie Group (G333)$$, because within 10-25 years they are very similar to naturally occurring sand barrens and oak barrens types in the surrounding landscape. Examples of recovery is also possible on other soil types.