Basal area - The cross-sectional area of a tree trunk measured in square 

 inches, square centimetres, etc. Basal area is normally measured at 4.5 ft 

 above the ground level and is used as a measure of dominance. The most easily 

 used tool for measuring basal area is a tape marked in square inches. When 

 plotless methods are used, an angle gauge or prism will provide a means for 

 rapidly determining basal area. This term is also applicable to the cross- 

 sectional area of a clumped herbaceous plant, measured at 1.0 in, above the 

 soil surface. 



Bench mark - A fixed, more or less permanent reference point or object, the 

 elevation of which is known. The US Geological Survey (USGS) installs brass 

 caps in bridge abutments or otherwise permanently sets bench marks at conveni- 

 ent locations nationwide. The elevations on these marks are referenced to the 

 National Geodetic Vertical Datum (NGVD) , also commonly known as mean sea 

 level (MSL) . Locations of these bench marks on USGS quadrangle maps are shown 

 as small triangles. However, the marks are sometimes destroyed by construc- 

 tion or vandalism. The existence of any bench mark should be field verified 

 before planning work that relies on a particular reference point. The USGS 

 and/or local state surveyor's office can provide information on the existence, 

 exact location, and exact elevation of bench marks. 



Biennial - An event that occurs at 2-year intervals. 



Buried soil - A once-exposed soil now covered by an alluvial, loessal, or 

 other deposit (including man-made). 



Canopy layer - The uppermost layer of vegetation in a plant community. In 

 forested areas, mature trees comprise the canopy layer, while the tallest 

 herbaceous species constitute the canopy layer in a marsh. 



Capillary fringe - A zone immediately above the water table (zero gauge 

 pressure) in which water is drawn upward from the water table by capillary 

 action. 



Chemical reduction - Any process by which one compound or ion acts as an elec- 

 tron donor. In such cases, the valence state of the electron donor is 

 decreased. 



Chroma - The relative purity or saturation of a color; intensity of distinc- 

 tive hue as related to grayness; one of the three variables of color. 



Comprehensive wetland determination - A type of wetland determination that is 

 based on the strongest possible evidence, requiring the collection of quanti- 

 tative data. 



Concretion - A local concentration of chemical compounds (e.g. calcium carbon- 

 ate, iron oxide) in the form of a grain or nodule of varying size, shape, 

 hardness, and color. Concretions of significance in hydric soils are usually 

 iron and/or manganese oxides occurring at or near the soil surface, which 

 develop under conditions of prolonged soil saturation. 



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