Physiognomy and Structure: This is a community with an open tree canopy, few woody shrubs, and extensive herbaceous ground cover. The density of trees as determined from General Land Office survey records was from 5-20 trees/ha on several sites in Wisconsin (Vogl 1961). It is very likely that more densely wooded examples of this community existed in the past as they can be seen currently in areas that have not been burned. At some level of canopy cover the site can no longer be classified as ~Pinus banksiana - (Quercus ellipsoidalis) / Schizachyrium scoparium - Prairie Forbs Wooded Herbaceous Vegetation (CEGL002490)$$ and is instead some type of woodland.

The density of the shrub layer appears to be related to the frequency of fire, the soil type, and the proximity of other, more closed forest types (Zimmerman 1956, MNNHP 1993). Sites close to the edge of extensive pine barrens have a more conspicuous shrub component. An increase in the fire interval also tends to allow more woody shrubs to proliferate. The density of the herbaceous layer is fairly constant, although some diminution of herbaceous cover occurs as the shrub layer becomes more closed. Tree canopy 10-20 m tall, short shrub 0.5-2 m and graminoid 0-2 m.

Floristics: The vegetation is dominated by grasses and forbs with a sparse tree layer. The dominant tree is Pinus banksiana, with varying amounts of Quercus ellipsoidalis, Pinus resinosa, Populus tremuloides, and Populus grandidentata. The composition of all the strata of this community can vary significantly. Pinus banksiana is a constant across all sites, but it can be virtually the only tree species present or one of many. Quercus ellipsoidalis or Quercus macrocarpa can outnumber Pinus banksiana on some sites, especially those that have not been burned for many years. Pinus resinosa is typically at low densities in most examples of this community. Dry sites tend to have fewer woody shrub species and more herbaceous species with sand prairie affinities. Among these are Dalea villosa, Koeleria macrantha, Prunus pumila, Schizachyrium scoparium, and Calamovilfa longifolia. Dry-mesic areas have more Andropogon gerardii, Amorpha canescens, Liatris aspera, and Hesperostipa spartea (= Stipa spartea). Patches of heath may occur, dominated by shrubby species such as Arctostaphylos uva-ursi, Comptonia peregrina, Hudsonia tomentosa, and Vaccinium angustifolium. Zimmerman (1956) also noted that stands of this community that are in the center of extensive sandplains have fewer deciduous tree species and shrubs.

The composition of all the strata of this community can vary significantly. Pinus banksiana is constant across all sites, but it can be virtually the only tree species present or one of many. Quercus ellipsoidalis can outnumber Pinus banksiana on some sites that have not been burned for many years. Pinus resinosa is typically at low densities in most examples of this community. Dry sites tend to have fewer woody shrub species and more herbaceous species with sand prairie affinities. Among these are Koeleria macrantha and Calamovilfa longifolia. Dry-mesic areas have more Andropogon gerardii, Amorpha canescens, and Hesperostipa spartea. Zimmerman (1956) also noted that stands of this community that are in the center of extensive sand plains have fewer deciduous tree species and shrubs. This community has scattered trees, little woody shrub component, and a fairly complete herbaceous cover. The dominant tree is Pinus banksiana, with varying amounts of Quercus ellipsoidalis, Pinus resinosa, and Populus spp. dominant in areas that have not been burned for many years. The shrub layer is more prominent near borders with other, more wooded communities. As the shrub layer increases there is some decrease in cover by the herbaceous layer.

Dynamics:  Fire is the most important natural disturbance in this community, keeping the tree canopy very open. This community is maintained by relatively common surface fires. These fires suppress the growth of a dense shrub layer while leaving most of the relatively fire-resistant canopy trees intact. The droughty conditions and infertile soils of this community retard the development of the shrub layer even when fire is absent. Oaks, especially Quercus ellipsoidalis and Quercus macrocarpa, are present as grubs and scattered trees when fire is frequent. Oaks can become a common part of the canopy in the absence of fire. Fire is also necessary for the successful germination of the dominant trees, Pinus banksiana and Pinus resinosa. Pinus banksiana also needs fire to open its serotinous cones and allow the seeds to be spread. These species are not shade-tolerant, and fire clears out competing species which otherwise might shade these pines out. Fire frequency and intensity must allow some older trees to survive or else the site will become a grassland or brushland. Fire intervals of 20-40 years are thought to allow for successful regeneration of the dominant species without killing all of the older trees (Vogl 1970). More frequent fires can all but eliminate the pines. Other natural disturbances which contribute to maintaining the open nature of these barrens are windthrow and icestorms.

In most areas this community was successionally stable due to recurrent fires. In the absence of fires the canopy of this community will begin to close over and more shade-tolerant species will begin to invade. This has occurred on many former examples of this community. The process is greatly slowed by the infertile and excessively drained soils on which this community occurs. In northern Minnesota, Almendinger (1986) found jack pine barrens that form a transition phase as the forest invades prairie. The sparse tree physiognomy exists only on sites that have had Pinus banksiana on them for a few hundred years. This seral stage is quickly invaded by shrubs because of the rich Mollisols on which it occurs. The shrubs shade out the prairie flora and soon a different community develops.