Physiognomy and Structure: The forests often form mono-dominant or mixed-dominance stands. Trees may still show evidence of being planted rows and be of uniform age. Regeneration of tree species, if present at all, rarely consists of the current overstory. Understory shrub and herb species can be sparse in old conifer plantations.

Floristics: The tree layer is dominated (>80% cover) by ruderal or generalist native tree species, or exotic/invasive tree species. The list of ruderal tree species are as follows: Conifers: Juniperus ashei, Juniperus virginiana, Pinus rigida, Pinus strobus, Pinus virginiana. Hardwoods: Acer negundo, Acer rubrum, Amelanchier spp., Betula populifolia, Crataegus spp., Crataegus crus-galli, Crataegus mollis, Diospyros virginiana, Fraxinus americana, Gleditsia triacanthos, Gymnocladus dioicus, Juglans nigra, Liquidambar styraciflua, Liriodendron tulipifera, Morus spp., Malus fusca, Morus rubra, Populus tremuloides, Prunus pensylvanica, and Prunus serotina. Naturalized exotics include the conifer Pinus thunbergii and hardwoods Acer platanoides, Ailanthus altissima, Catalpa bignonioides (exotic in Canada), Morus alba, Paulownia tomentosa, and Robinia pseudoacacia (although a native in the central hardwoods region, it is so widely planted outside of its range that it is essentially exotic in character). Both the ruderal natives and naturalized exotic species often form mono-dominant or mixed-dominance stands. Common conifer planted tree species in old or abandoned plantations include Larix decidua, Picea abies, Picea glauca, Pinus banksiana, Pinus resinosa, Pinus strobus, Pinus sylvestris, and Pinus virginiana. A variety of old hardwood planted species may also occur, including Prunus serotina, Juglans nigra, Populus spp., and Robinia pseudoacacia. Understory shrub and herb species in all stands vary from exotic invasives to native generalists. Invasive shrub species include a variety of honeysuckles (Lonicera japonica, Lonicera morrowii, Lonicera tatarica, Lonicera x bella), Rhamnus cathartica, and others.

Dynamics:  Stands are a later stage in the development of vegetation on sites that were heavily disturbed by humans, including plowing, grading, skidding, etc. Earlier stages of vegetation on abandoned agricultural sites include old fields dominated by annual and perennial weeds, grasses and shrubs, as described by ~Eastern North American Ruderal Grassland & Shrubland Macrogroup (M123)$$. Sometimes these later stages are facilitated by planting trees. Because the extensive soil disturbances typically lead to a mix of weedy native and exotic shrub and herb species, the stands take on a strongly ruderal composition, even if native trees invade or are planted. Canopy cover may be as low as 10%, but eventually stands may have more-or-less continuous canopy, leading to a shift to a more shade-tolerant ground layer. Succession of old fields to ruderal forests has been well-documented. Wright and Fridley (2010) recently showed that there are biogeographic and latitudinal patterns to the development of these forests. Further information on the dynamics of this type can be found in the many references provided by them.

Stands may also originate from abandoned forest plantation stands (tracked in 7. ~Agricultural & Developed Vegetation Cultural Class (CCL01)$$). The planted trees begin to die out, and the ground layer is invaded by native species.

There may be a range of responses of forests to various human and natural disturbances (Foster 2000). The ruderal forests described here have a current combination of characteristics that show a strong deviation from the native forests that historically occupied the site and which persist today (Singleton et al. 2001, Bellemare et al. 2002). For example, Bellemare et al. (2002) compared primary rich mesic forests (logged, but never cleared) with secondary forests that established on former agricultural lands in western Massachusetts. They found that species with seeds lacking morphological adaptations for dispersal (barochores) (e.g., Cardamine diphylla, Tiarella cordifolia), those with adaptations for ant dispersal (myrmecochores) (e.g., Asarum canadense, Claytonia caroliniana) or strictly clonal (Cardamine maxima) are common in primary forest, but are less frequent or absent in nineteenth and twentieth century secondary stands. In contrast, species with fruits consumed and dispersed by vertebrates (endozoochores) or dispersed by the wind (anemochores) and which are common in primary forest (e.g., Arisaema triphyllum, Caulophyllum thalictroides, Eurybia divaricata, Polystichum acrostichoides) have colonized many secondary stands, often within a few decades of stand initiation. Where invasive tree, shrub or herb species have not established (as appears to be the case for their study), these secondary stands may recover enough diagnostic species to be classified as depauperate examples of rich mesic forest. But if their composition is predominantly ruderal native and invasive species, they would be classified as this macrogroup.