Herbaceous layer - Any vegetative stratum of a plant community that is 

 composed predominantly of herbs. 



Histic epipedon - An 8- to 16-in. soil layer at or near the surface that is 

 saturated for 30 consecutive days or more during the growing season in most 

 years and contains a minimum of 20 percent organic matter when no clay is 

 present or a minimum of 30 percent organic matter when 60 percent or greater 

 clay is present. 



Histosols - An order in soil taxonomy composed of organic soils that have 

 organic soil materials in more than half of the upper 80 cm or that are of any 

 thickness if directly overlying bedrock. 



Homogeneous vegetation - A situation in which the same plant species associa- 

 tion occurs throughout an area. 



Hue - A characteristic of color that denotes a color in relation to red, yel- 

 low, blue, etc; one of the three variables of color. Each color chart in the 

 Munsell Color Book (Munsell Color 1975) consists of a specific hue. 



Hydric soil - A soil that is saturated, flooded, or ponded long enough during 

 the growing season to develop anaerobic conditions that favor the growth and 

 regeneration of hydrophytic vegetation (US Department of Agriculture-Soil 

 Conservation Service 1985) . Hydric soils that occur in areas having positive 

 indicators of hydrophytic vegetation and wetland hydrology are wetland soils. 



Hydric soil condition - A situation in which characteristics exist that are 

 associated with soil development under reducing conditions. 



Hydrologic regime - The sum total of water that occurs in an area on average 

 during a given period. 



Hydrologic zone - An area that is inundated or has saturated soils within a 

 specified range of frequency and duration of inundation and soil saturation. 



Hydrology - The science dealing with the properties, distribution, and circu- 

 lation of water. 



Hydrophyte - Any macrophyte that grows in water or on a substrate that is at 

 least periodically deficient in oxygen as a result of excessive water content; 

 plants typically found in wet habitats. 



Hydrophytic vegetation - The sum total of macrophytic plant life growing in 

 water or on a substrate that is at least periodically deficient in oxygen as a 

 result of excessive water content. When hydrophytic vegetation comprises a 

 community where indicators of hydric soils and wetland hydrology also occur, 

 the area has wetland vegetation. 



Hypertrophied lenticels - An exaggerated (oversized) pore on the surface of 

 stems of woody plants through which gases are exchanged between the plant and 

 the atmosphere. The enlarged lenticels serve as a mechanism for increasing 

 oxygen to plant roots during periods of inundation and/or saturated soils. 



A6 



