Ecological dynamics

The information in this ecological site description (ESD), including the state-and-transition model (STM), was developed using archeological and historical data, professional experience, and scientific studies. The information is representative of a complex set of plant communities. Not all scenarios or plants are included. Key indicator plants, animals, and ecological processes are described to inform land management decisions.

Introduction – Southern Arkansas, western Louisiana, and eastern Texas have been deemed the Pineywoods because of the vast expanse of pine trees. The region represents the western edge of the southern coniferous belt. Historically, the area was covered by pines with mixed hardwoods, sparse shrubs, and a diverse understory of grasses and forbs. Fire played a significant role in reducing the woody competition that generally out-competes the herbaceous understory layer. Fire suppression and land conversion have reduced the amount of historical communities in existence today.

Background – Prior to settlement by the Europeans, the reference state for the Clayey Bottomland ecological site was a Overcup Oak/Water Hickory (Quercus lyrata/Carya aquatica) Forest. Remnants of this presumed historic plant community still exist where natural conditions are replicated through conservation management techniques. Evidence of the reference state is found in accounts of early historic explorers to the area, historic forest and biological survey teams, as well as recent ecological studies in the last 30 years. The age of this woodland community varies, and has a diverse understory of grasses and forbs.

Settlement Management – As human settlement increased throughout the area, so did the increase in logging and grazing by domestic livestock. Oftentimes, an early settler would make camp by logging pines in the area for lodging. The accompanying livestock would graze the upland woodlands filled with warm-season forage during the summer. As the summer grazing season would end, the livestock would naturally begin grazing in the bottoms to forage on large cane breaks and other cool-season plants found in the area. The bottomlands also provided plentiful hunting opportunities for deer, turkey, and squirrel that utilize the acorn crop.

Eventually, the logging became so extensive that by the 1930’s most of the region had been cut-over. Replanting trees to historic communities was not common and early foresters began planting loblolly pine (Pinus taeda) for its quick growth. The loblolly pines were commonly grown plantation style (site preparation, planting, long-term weed control, etc). This, coupled with the advent of heavy site preparation machinery made the conversion from low-grade hardwood possible.

Current Management and State – Today much of the remnant forest is gone, replaced by tree plantations, crops, and pastures. The largest bottomlands of disappearance are areas converted to reservoirs, including Sam Rayburn and Toledo Bend. The areas that have not been converted retain resemblance to pre-settlement conditions. Fire is not a large driver in the bottomlands, hence fire suppression does not play a large role in shaping the forested communities.

Fire Regimes – Fire was a natural and important disturbance throughout the Western Gulf Plain. Fire occurred naturally and was started by Native Americans for game movement, insect control, travel, and many other reasons. Contrary to most of the region, the bottomland communities developed with a very infrequent fire regime. The bottomlands are estimated to have burned one in every 50 years. Bottomlands naturally retard fire in a number of ways. Frequent flooding inundates the sites for sometimes months, and fire cannot travel. Another reason for reduced fire intervals is the understory vegetation is somewhat sparse of fine-fuel materials compared to those in the uplands. Coupled with the thicker, fire-resistant leaves adorning much of the vegetation, the bottomlands do not burn very often.

Disturbance Regimes – Extreme weather events occur occasionally throughout the region. Tornados uproot trees and open canopies in the spring months. In the late summer and early fall, hurricanes or tropical depressions often make landfall, dumping excessive amounts of rain and toppling trees with high winds. Flooding events occur most years in which rainfall is normal or higher. Prolonged flooding due to excessive precipitation can cause mortality in vegetative species that are unable to handle the continuous water, especially during the growing season (March through September). Reservoirs affect the natural flooding regimes. Upstream areas remain flooded longer and the frequency and duration of flooding on downstream areas are also impacted.

Plant Community Interactions – The dominant force in shaping the bottomlands is the close-proximity to a water source that floods the site throughout the year. Flooding for one to three months during the dormant season gives rise to plants that tolerate a wetter environment. Micro-relief within the broadly delineated bottomlands also affects the plant dispersion. Plants more adapted to water grow in the lower micro-elevations, and those that are more facultative (less water tolerant) occupy the higher micro-elevations. The difference between the upper and lower elevations could be as little as inches. The loamy surface of the ecological site has gleyed subsoils resulting from lack of oxygen during flooding. The communities are dominated by hardwood trees and an understory that can tolerate the varying conditions accompanying the floods.