Upland Oak-Hickory Forest
The oak-hickory forests of Buffalo National River are dominated by black oak (Quercus velutina), white oak (Quercus alba), and mockernut hickory (Carya tomentosa). The understory is comprised of a variety of native trees, shrubs, forbs, and grasses. The majority of oak-hickory forest within the park is second growth indicating past use for lumber.
Oak-hickory forests are fire dependent and will shift towards less fire tolerant species such as sugar maple in the absence of fire or disturbance. Sugar maple in particular has invaded portions of the oak-hickory forests at the national river where it is rapidly outcompeting the oak species. Exotic vegetation is minimal in the oak-hickory forests of the park.
Oak-pine forests occur mainly on south-facing slopes within the park although they also occur in other areas. Dominant trees are shortleaf pine (Pinus echinata) and a variety of oak and hickory species with a variety less dominant hardwoods.
The oak-pine ecotype is fire-dependent; fire prepares a seedbed beneficial to both oaks and shortleaf pine. In the absence of fire less tolerant tree species invade and effect the reproductive success of oak and pine species by shading and out-competing oak and pine seedlings. The Association for Biodiversity Information (ABI) rates the status of habitat types based on their abundance, distribution, and susceptibility. The oak-pine woodlands of Arkansas have received a ranking of G2/G3; imperiled to vulnerable based on the few number of high quality examples of this habitat type due to fire suppression, forest conversion, and development.
The post-oak barrens of Buffalo National River represent transitional zones between glades and hardwood forests. Typically, they occur on shallow soils and contain floristic elements of both glades and forests. Prairie forbs are common under the open tree canopy characteristic of barrens (10-50% tree cover). The dominant trees of the barrens, post oak (Quercus stellata) and black-jack oak (Quercus marilandica) are well adapted to shallow soils, drought, and fire that are the natural perturbations of this ecotone. Barrens or savannas often yield the highest diversity of plants and wildlife in the Midwest because they support both prairie and forest species and are uniquely adapted to natural disturbances.
Within Buffalo National River, post-oak barrens occur in isolated patches on dry, rapidly drained, shallow soils. This forest is best developed on south- and west-facing slopes and ridgetops of steep-walled valleys and canyons. The tree canopy is short (20-50 feet), slow-growing, and open due to slow replacement of fallen timber. Tree crowns are spreading, open, and limby. The understory is poorly developed and consists of widely scattered shrubs. Typical species include Vaccinium arboreum, Amelanchier arborea, and Ostrya virginiana. In Arkansas, herbaceous species include Carex umbellata and Carex hirsutella .
Several studies of the post-oak barrens of the Buffalo National River have recorded the vegetative species present and the effects of prescribed fire on the vegetation present. The studies reveal that without fire, the post-oak barrens would eventually become forests and could lose the diverse qualities they now possess.
The glades of Buffalo National River are found associated with rock outcrops and in areas where soils are generally shallow and poor. They consist of open rocky areas with clumps of grasses, eastern red cedar (Juniperus virginiana), and small hardwood saplings. Eastern red cedar is a pioneer tree species able to thrive in shallow soils and harsh environmental conditions. Without management actions, the glades will fill with cedar and once soil is formed, other tree species will invade. The flora and fauna associated with glades are unique and the park desires to promote this habitat type in order to protect these species. Glades require disturbance such as storms, fires, and droughts to maintain their vegetative composition.
Cane (Arundinaria gigantea) is a native woody bamboo that forms monotypic stands known as canebrakes. Once widespread in Ozark floodplains, canebrakes are now imperiled ecosystems, reduced to less than 2% of former range. Canebrakes are fire dependent plant communities: in the absence of fire, woody species rapidly outcompete and replace cane. Cane burns readily and resprouts from rhizomes. Historic research indicates that a 10-year fire return interval will maintain the ecology of canebrakes. A shorter interval will favor the establishment of fire-tolerant trees and shrubs, and a longer interval will allow the establishment of riparian forest.
Riparian, floodplain, or bottomland forests are found along the Buffalo River and its tributaries. Dominant tree species are American elm (Ulmus americana), green ash (Fraxinus americana), silver maple (Acer saccharinum), box elder (Acer negundo), sycamore (Platanus occidentalis), river birch (Betula nigra), black willow (Salix nigra), and cottonwood (Populus deltoides). The cottonwoods are confined to sandy areas associated with gravel bars. Gravel bars themselves are dominated by a variety of willow species.
Floodplain forests develop where soils are rich, wet, and deep. They perform important functions; reducing soil loss during flood events, providing habitat for riparian wildlife; and provision of organic matter to streams. Due to the high fertility of the floodplain forest soils, many floodplains have been converted to agricultural use.
Agricultural use within the watershed of the Buffalo River is considered an important cultural landscape element; reflecting historic use and social conditions of the early settlers. Therefore, in areas that were riparian forest prior to settlement some agricultural use is permitted and desired to reflect the historic scene.
Beech forest occurs on north facing slopes in moist ravines in the western portion of the Buffalo National River. This forest is found on sheltered slopes, ravines, and upper terraces. The closed forest canopy is dominated by Fagus grandifolia. Codominance by one or more of the following trees: Quercus rubra, Quercus alba, Tilia americana, and Fraxinus americana is usual. The shrub stratum is open to moderately dense. The herb stratum is lush and diverse but can vary in composition from site to site depending on soil fertility and past disturbance. Beech forests develop under wet conditions in the absence of fire. Fire return intervals for beech forest are in excess of 500 years . The presence of beech forest indicates the presence of well-developed soils, permanent groundwater, and a minimum of disturbance.