Ozark-Ouachita Shortleaf Pine-Bluestem Woodland

This system represents woodlands of the Ouachita and Ozark mountains region of Arkansas, adjacent Oklahoma, and southern Missouri in which Pinus echinata is the canopy dominant, and the understory is characterized by Andropogon gerardii, Schizachyrium scoparium, and other prairie plants. Although examples of this system occur throughout this region, there is local variation in the extent to which they were present. The center of distribution is the northern and western Ouachita Mountains, and it is best developed in large, dry, and flat to gently undulating portions of the landscape which carry fire well, creating extensive natural fire compartments. In the Ouachitas, the system occurs on the northern Hogback Ridges excluding the Novaculite areas to the south. These are large, gently sloping, east/west-trending ridges of sandstone and shale, the south-facing slopes of which constitute large fire compartments. In nearly all examples, Pinus echinata occurs with a variable mixture of hardwood species. The exact composition of the hardwoods is much more closely related to aspect and topographic factors than is the pine component. In the Ozark Highlands this system is less extensive but was historically prominent where sandstone-derived soils are common. In Missouri and Oklahoma, this system occurs on gently dissected upland cherty plains (in addition to sandstone ridges).

In the northern part of this geographic area Pinus echinata, xeric oaks and some hickory dominate the overstory with a high percentage of oak on steep north slopes and on Quercus stellata flats. Associated species include Quercus marilandica and Carya tomentosa (= Carya alba) on drier sites and to the west Carya texana. In some examples of this system, the aggregate importance of hardwoods may be greater than pine, especially on subxeric and mesic sites (Dale and Ware 1999). Pine is often the canopy emergent on upper slopes. Stand density increases with available moisture. Typical shrubs may include Vaccinium arboreum, Vaccinium pallidum, and Vaccinium stamineum, but these patches are rare. Various bluestem grasses, legumes and other forbs dominate the understory (herbaceous layer).

This system occurs throughout the Ouachita and Ozark mountains region, and there is some local variation in the extent to which it is present. The system is best developed in large portions of the landscape which are flat to gently undulating and which would carry fire well, creating extensive natural fire compartments. In the Ouachitas, the system occurs on the northern Hogback Ridges, which are large, gently sloping, east/west-trending ridges of sandstone and shale, the south-facing slopes of which constitute large fire compartments. In nearly all examples, Pinus echinata occurs with a variable mixture of hardwood species. The exact composition of the hardwoods is much more closely related to aspect and topographic factors than is the pine component. In the Ozark Highlands this system is less extensive but was historically prominent where sandstone-derived soils are common. In Missouri and Oklahoma, this system occurs on gently dissected upland cherty plains (in addition to sandstone ridges). This system is primarily confined to gently to moderately sloping, upland plains (larger fire compartments) and is thereby distinguished from shortleaf pine-oak woodland, which occurs on more steeply dissected ridges and steep southwest-facing slopes (smaller fire compartments). In the Ouachitas, the primary pine-bluestem landscape lies to the north of the two tallest ridges, Blackfork Mountain and Rich Mountain, which form a rainshadow by orographic lifting of the moisture-laden winds from the Gulf of Mexico that strongly influence the climate of this region; precipitation on those ridges can be as high as 147 cm (58 inches) annually, while just to the north, it may fall to 117 cm (46 inches) (T. Foti pers. comm. 2013).

This system is Fire Regime Group I (Landfire 2007a), with frequent surface fires. Area fire frequency is 3 to 4 years, and the mean fire-return interval ranges from 1 to 12 years (Masters et al. 1995). Annual fire was common historically, such as in the 1800s. Replacement and mixed-severity fires are infrequent, every 100 to 1000 years. Stand-replacement fires occurred mostly under extreme drought conditions during the growing season. The impact of native ungulate grazing (buffalo and elk) was negligible, but fire generally maintained these open woodlands. Drought and moist cycles play a strong role interacting with both fire and native grazing. Other disturbance types include ice storms, wind events, and insect infestations. These disturbances can add significantly to downed woody debris, which can add fuel and increase fire intensity when that downed material is dry and burns. Pinus echinata has shorter needles and is not as susceptible to ice as Pinus taeda, which is more common further south in Arkansas.

Fire is an important dynamic process, which maintains open woodland conditions and can promote oak and pine regeneration. Today the region consists largely of closed-canopy forests, though relatively frequent fires prior to Euro-American settlement created and maintained forests, woodlands, savannas and glades (Stambaugh and Guyette 2006). Prior to 1820, fires were most frequent in areas with low topographic roughness, such as flat or gently sloping lands away from ravines and creeks (Stambaugh and Guyette 2008). For the next hundred years, fires increased as population increased (Stambaugh and Guyette 2006, 2008), until about 1930 when very effective fire-suppression practices began (Guldin et al. 2005). During the 1800s, these fires helped maintain Pinus echinata woodlands with floristically rich understory vegetation of prairie grasses and forbs (Hedrick et al. 2007). There is a very low rate of fire ignitions from lightning strikes in the area, nearly all ignitions are caused by people (Stambaugh and Guyette 2006).

Lack of fire is a big threat. Without fire, the development of a closed forest canopy can lead to declines in the native herbaceous ground cover vegetation, especially the grasses which are more typical of open prairies. Clearcut logging of Pinus echinata, and forest succession by hardwood trees, or planting of Pinus taeda are threats to Pinus echinata woodlands. Pinus echinata woodlands have declined due to conversion to intensively managed pine plantations. Often sites have been replanted with Pinus taeda, and are then no longer burned for forest management. Some stands do not have adequate reproduction with restoration thinnings and prescribed fire, and will need to have Pinus echinata seedlings planted to regenerate stands (Guldin et al. 2005).

This system occurs in the Ouachita and Ozark mountains region of Arkansas, adjacent Oklahoma, and southern Missouri.