bottomland forest

BOTTOMLAND FORESTS

Wetland Ecology and Management

Course Codes: NATR 5250/6250

Terms and Concepts

  • Bottomland hardwood forest: A type of forest found in the low-lying areas along rivers subject to flooding and having a diverse composition of hardwood trees.

  • Floodplain forest: Forested areas adjacent to rivers and streams that are subject to periodic flooding.

  • Riparian zone: The interface between land and a river or stream, characterized by vegetation that interacts with the aquatic ecosystem.

  • Open system: An ecosystem where energy and nutrients are exchanged with the environment.

  • Landform gradients: Variations in landforms that affect ecological processes, including:

    • Continental gradients: Variations due to east-west and latitudinal climatic gradients at the hydrologic basin level.

    • Intra-riparian gradients: Variations within the riparian zones reflecting changes in elevation, stream gradient, and other fluvial processes.

    • Trans-riparian gradients: Variations across the riparian zone affecting local moisture and soil development.

  • Natural levees: Elevated banks adjacent to rivers formed by sediment deposits during flooding.

  • Meander scrolls: Landforms created as rivers bend and deposit sediment in their floodplains.

  • Back swamp: Low-lying areas behind natural levees that can flood frequently.

  • Point bars: Depositional features on the inside bends of meanders where sediments accumulate.

  • Oxbows: Crescent-shaped lakes formed when a meander is cut off from the river.

  • Terrace: Flat areas along the sides of a valley formed by river processes over time.

  • Redwater river/floodplain: Floodplains associated with rivers that carry sediment originating from upland areas, usually having moderate soil organic matter.

  • Blackwater river/floodplain: Floodplains of rivers that are often acidic and low in nutrients, originating in peatlands.

  • Soil and water chemistry: The study of the chemical composition and processes within the soils and waters of these ecosystems.

  • Tree succession/species diversity: The changes in tree species composition over time and the variety of species present.

  • Animal diversity: The range of animal species inhabiting the ecosystem.

Case Studies

  1. Amite River Floodplain, LA

  2. Little River National Wildlife Refuge Bottomland Hardwood Forest, OK

  3. Lower Mississippi River Floodplain, MS

Characteristics of Riparian Ecosystems

  • High water table: A water level close to the surface, influencing vegetation.

  • Ecotone: A transitional area between aquatic and upland ecosystems characterized by unique species composition.

  • Species diversity: Riparian ecosystems have high species diversity, densities, and productivity due to favorable conditions for growth.

  • Ecosystem interactions: Interactions between aquatic and terrestrial ecosystems can enhance overall ecosystem function.

  • Open systems: Such ecosystems integrate nutrients and energy from both aquatic and terrestrial sources.

Relationship of Riparian Ecosystems to Wetlands

  • Wetlands are classified as a subset of riparian ecosystems characterized by water persistence and associated vegetation.

  • The overlapping features of wetlands include:

    • Low water level: Often found within the bounds of the riparian zone.

    • High water level: May fluctuate between low and high, affecting the types of vegetation that can thrive.

Bottomland Hardwood Forests as Mesic Riparian Ecosystems

Features of Bottomland Hardwood Forests

  1. Hydrology: The habitat experiences periodic flooding or saturation of soil during growth seasons.

  2. Saturated Soils: The root zone soils become flooded or saturated periodically throughout the growing season.

  3. Woody Vegetation: The prevalent woody species exhibit adaptations that allow survival and reproduction in anaerobic conditions.

Major Landform Gradients in Riparian Zones

  1. Continental/Regional Gradients: Effects from east-west and latitudinal climatic differences impacting hydrology.

  2. Intrariparian Gradients: Vertical changes along a stream's course reflecting physical and biological variances.

  3. Transriparian Gradients: Local topographic changes affecting soil moisture and development in the riparian zone.

Major Geomorphologic Features of Southeastern U.S. Floodplain

  • Terrace features: Elevated lands parallel to the river, including natural levees and back swamps.

  • Floodplains: Flat areas next to rivers subject to erosion and sediment deposition.

  • Meander scrolls: Result from the sedimentary processes associated with river bends.

  • Oxbow lakes: Formed when a river changes course, leaving behind a curvilinear body of water.

Floodplain Development Sequences

Two development sequences of floodplains and river terraces:

  • Sequence A: Erosion of valley floor followed by deposition of alluvial fill.

  • Sequence B: Erosion of initial deposits followed by deposition of a secondary alluvial layer.

Climate and Hydrology

  • Hydrology in floodplains is directly connected to rainfall patterns. In the Southeast:

    • Rainfall is consistent year-round, with higher runoff during winter and spring.

    • More seasonal rainfall conditions exist near coastal regions.

  • Hydroperiod: The duration, depth, intensity, and timing of flood waters dictate both ecological structure and species composition.

Soils and Water Chemistry

Physiographic Origin

  • Redwater vs. Blackwater Floodplains: Defined by their origins and sediment content.

Redwater Floodplains

  • Origin in the Piedmont/Appalachians, characterized by:

    • High nutrient levels from sediment and mineral content.

    • Moderate soil organic matter (2-5%).

Blackwater Floodplains

  • Originates in Coastal Plains, featuring:

    • High carbon content and tannins, resulting in acidic conditions.

    • Lower gradient and hydrology characterized by rainwater inputs.

    • Higher soil organic matter (>5%).

Nutrient Cycling

  • Open Systems: Rich in nutrient inputs and outputs; deepwater swamps serve as nutrient sinks against nutrient transport.

  • Adsorption of phosphorus (P) to sediments plays a critical role in nutrient cycling.

Floodplain Tree Succession

  • Dynamic influenced by:

    • Hydrologic Conditions: Frequent flooding can affect species composition.

    • Disturbance Regime: Both natural and anthropogenic alterations impact succession dynamics.

Vegetation Associations and Floodplain Topography

  • Relationship between vegetation and topography of southeastern U.S. bottomland hardwood forests, reflecting flooding duration and frequency. This includes tree species responses:

    • Seldom Flooded, Continuous Flooding, Seasonally Flooded, among others, each associated with specific tree species.

Primary Productivity in Riparian Ecosystems

  • High productivity due to:

    • Abundant water supply from flooding.

    • Nutrient delivery and improved soil chemistry from flooding.

    • Oxygenation of root zones from flowing water during floods.

    • Flooding acts both as a subsidy and a stressor to ecosystems.

Regional Animal Richness

  • Influenced by:

    • Edge Effects: Different habitats adjacent to one another can support diverse species.

    • Water Availability: Critical to sustain various species.

    • Habitat Diversity: Multiple habitats promote a range of species.

    • Corridors: Connectivity between habitats enabling movement and migration of fauna.

Distribution of Animals in Southern Bottomland Hardwood Forests

Amphibians, Reptiles, and Mammals

  • Notable species include:

    • River Otter, Raccoon, Beaver, White-Tailed Deer, Alligator, and various snakes and frogs.

Birds related to Nesting and Foraging

  • Notable species and their roles include:

    • Pileated Woodpecker, Hooded Merganser, Ruby-Crowned Kinglet, Bald Eagle, Wood Duck, with classifications based on nesting (N), summer foraging (SF), and winter foraging (WF).