Overbank flooding - Any situation in which inundation occurs as a result of 

 the water level of a stream rising above bank level. 



Oxidation-reduction process - A complex of biochemical reactions in soil that 

 influences the valence state of component elements and their ions. Prolonged 

 soil saturation during the growing season elicits anaerobic conditions that 

 shift the overall process to a reducing condition. 



Oxygen pathway - The sequence of cells, intercellular spaces, tissues, and 

 organs, through which molecular oxygen is transported in plants. Plant 

 species having pathways for oxygen transport to the root system are often 

 adapted for life in saturated soils. 



Parameter - A characteristic component of a unit that can be defined. Vegeta- 

 tion, soil, and hydrology are three parameters that may be used to define 

 wetlands. 



Parent material - The unconsolidated and more or less weathered mineral or 

 organic matter from which a soil profile develops. 



Ped - A unit of soil structure (e.g. aggregate, crumb, prism, block, or 

 granule) formed by natural processes. 



Peraquic moisture regime - A soil condition in which a reducing environment 

 always occurs due to the presence of ground water at or near the soil surface. 



Periodically - Used herein to define detectable regular or irregular saturated 

 soil conditions or inundation, resulting from ponding of ground water, precip- 

 itation, overland flow, stream flooding, or tidal influences that occur(s) 

 with hours, days, weeks, months, or even years between events. 



Permeability - A soil characteristic that enables water or air to move through 

 the profile, measured as the number of inches per hour that water moves 

 downward through the saturated soil. The rate at which water moves through 

 the least permeable layer governs soil permeability. 



Physiognomy - A term used to describe a plant community based on the growth 

 habit (e.g., trees, herbs, lianas) of the dominant species. 



Physiological adaptation - A feature of the basic physical and chemical 

 activities that occurs in cells and tissues of a species, which results in it 

 being better fitted to its environment (e.g. ability to absorb nutrients under 

 low oxygen tensions) . 



Plant community - All of the plant populations occurring in a shared habitat 

 or environment. 



Plant cover - See areal cover. 



Pneumatophore - Modified roots that may function as a respiratory organ in 

 species subjected to frequent inundation or soil saturation (e.g., cypress 

 knees) . 



A9 



