Midwestern Dry Oak Forest

This system is found throughout the glaciated regions of the Midwest, typically in gently rolling to flat landscapes. It can occur on uplands within the prairie matrix or within the context of dry-mesic oak-hickory forests and oak savannas. These are common on rolling glacial moraines and outwash plains. Soils are typically well-drained to excessively drained Mollisols or Alfisols that range from sand to sandy loam in texture. Historically, this type was quite extensive in Michigan, Indiana, Illinois, Missouri, Iowa, Wisconsin, and Minnesota. It is distinguished from other forested systems within the region by a dry edaphic condition that is transitional between dry prairies, oak barrens, or savannas and dry-mesic oak-hickory forests and woodlands. Forest cover can range from dense to moderately open canopy. Fire-resistant oak species, in particular Quercus velutina, Quercus macrocarpa, Quercus coccinea, and Quercus ellipsoidalis, dominate the overstory. Carya glabra, Prunus serotina, and Sassafras albidum are also common in portions of the range of this system. Depending on range of distribution and overstory canopy density, the understory may include species such as Gaylussacia baccata (in Michigan, Wisconsin, and Minnesota), Vaccinium angustifolium, and Rhus aromatica, and/or a mixture of woodland and grassland species, including Schizachyrium scoparium, Deschampsia flexuosa, and Carex pensylvanica. Extreme drought, along with periodic ground and crown fire events, constitute the main natural processes for this type and likely maintained a more open canopy structure that supported oak regeneration. In fact, many current examples of this type have resulted from long-term fire suppression and conversion of oak barrens to these forests and woodlands. Fire suppression may also account for examples of this system with the more dry-mesic understory. It likely has allowed for other associates such as Quercus rubra and Fraxinus americana to become more prevalent. Extensive conversion for agriculture in the surrounding landscape with more productive soils has fragmented and isolated examples of this system. It is found primarily within the "corn belt" of the United States, and remaining large areas of this system are likely under considerable pressure due to conversion to pastureland and urban development.

Forest cover can range from a dense to moderately open canopy. Fire-resistant oak species, in particular Quercus velutina, Quercus macrocarpa, Quercus coccinea, and Quercus ellipsoidalis, dominate the overstory. Carya glabra, Prunus serotina, and Sassafras albidum are also common in portions of the range of this system. Depending on range of distribution and overstory canopy density, the understory may include species such as Gaylussacia baccata (in MI, WI, and MN), Vaccinium angustifolium, and Rhus aromatica, and/or a mixture of woodland and grassland species, including Schizachyrium scoparium, Deschampsia flexuosa, and Carex pensylvanica.

This system can occur on uplands within the prairie matrix or within the context of dry-mesic oak-hickory forests and oak savannas. These are common on rolling glacial moraines and outwash plains and, less frequently, old dunes. Soils are typically well-drained to excessively drained Mollisols or Alfisols that range from sand to sandy loam in texture. Dry soils or landscape position (steep slopes, upper slopes, south- or west-facing aspect) favor the formation of this system. Historically, this type was quite extensive in Michigan, Indiana, Illinois, Missouri, Iowa, Wisconsin, and Minnesota. It is distinguished from other forested systems within the region by a dry edaphic condition that is transitional between dry prairies, oak barrens, or savannas and dry-mesic oak-hickory forests and woodlands.

Extreme drought, along with periodic ground and crown fire events, constitute the main natural processes for this type and likely maintained a more open canopy structure that supported oak regeneration. In fact, many current examples of this type have resulted from long-term fire suppression and conversion of oak barrens to these forests and woodlands. Frequency of fires necessary to maintain this system varied, largely depending on soil fertility and drainage, with more fertile and mesic sites requiring more frequent fires. Fire-return intervals of 5-20 years would typically maintain a woodland or oak grub shrubland, while fire-return intervals of 20-50 years would typically maintain a closed canopy oak forest (Landfire 2007a). Fire suppression may also account for examples of this system with the more dry-mesic understory. It likely has allowed for other associates such as Quercus rubra and Fraxinus americana to become more prevalent.

Fire suppression and conversion to agricultural or urban uses are the major threats to this system. Fire suppression has resulted in more closed-canopy forests with little or no oak regeneration and invasion by fire-intolerant trees, such as Acer spp., Celtis occidentalis, Fagus grandifolia, Liriodendron tulipifera, Prunus serotina, and Sassafras albidum, and understory species (Nowacki and Abrams 2008). Extensive conversion for agriculture in the surrounding landscape with more productive soils has fragmented and isolated examples of this system. It is found primarily within the "corn belt" of the United States, and many remaining large areas of this system are under considerable pressure due to conversion to pastureland and urban development. Stands can be significantly affected by insect defoliators Spongy Moth (Lymantria dispar) and forest tent caterpillar (Malacosoma disstria). Long-term effects from these have been limited in this system, but significant mortality in Quercus-dominated stands in the northeastern U.S. has been noted due to Spongy Moth defoliation (Davidson et al. 2001). Heavy deer browsing is not as common as in more mesic systems but can affect the understory and tree seedlings, reducing many native forbs and tree seedlings (Healy 1997, Rooney 2001). White-tailed deer have been shown to browse oak seedling over maple seedlings (Stroke and Anderson 1992). Invasive plant species that threaten the diversity and structure include Alliaria petiolata, Celastrus orbiculata, Cynanchum louiseae (= Vincetoxicum nigrum), Cynanchum rossicum (= Vincetoxicum rossicum), Elaeagnus umbellata, Lonicera japonica, Lonicera maackii, Lonicera morrowii, Lonicera sempervirens, Lonicera tatarica, Lonicera x bella, Lonicera xylosteum, Rhamnus cathartica, and Rosa multiflora (Kost el al. 2007).

Found throughout the glaciated regions of the Midwest.