Playa - Periodically flocxled wetland basin common in parts of the Southwest. 



Pneumatophore - Modified roots rising above ground that may function as a respiratory organ in species 

 subjected to frequent inundation or soil saturation. 



Podzolization - The process by which sesquioxides (aluminum and iron) are leached from the A-horizon 

 and precipitated in the B-horizon, often resulting in a leached layer, the E-horizon. 



Polymorphic (leaves) - Two or more different types of leaves formed on plants; in wetland plants, poly- 

 morphic leaves may develop due to extended flooding. 



Ponded - A condition in which free water covers the soil surface, for example, in a closed depression; the 

 water is removed only by percolation, evaporation, or transpiration. 



Poorly drained - A condition in which water is removed from the soil so slowly that the soil is saturated 

 periodically during the growing season or remains wet for long periods greater than 7 days. 



Pothole - A depressional weUand commonly found in Upper Midwest (North and South Dakota and west- 

 em Minnesota) and similar wetiands found elsewhere. 



Prevalence index - A weighted average measure of the sum of the frequency of occurrences of all species 

 along a single transect or as calculated for a plant community by averaging the prevalence index of all sam- 

 ple transects through the community. 



Problem area wetiand - A wetland that is difficult to identify because it may lack indicators of wetiand hy- 

 drology and/or hydric soils, or its dominant plant species are more common in nonwetlands. 



Profile - Vertical section of the soil through all its horizons and extending into the parent material. 



Quadrat - Sample units or plots that vary in size, shape, number, and arrangements, depending on the na- 

 ture of the vegetation, site conditions, and purpose of study. 



Quantitative - A precise measurement or determination expressed numerically. 



Range - The set of conditions throughout which an organism (e.g., plant species) naturally occurs. 



Reduction - The process of changing an element from a higher to a lower oxidation state as in the reduction 

 of ferric (FeS-n) iron into ferrous iron (Fe2+). 



Relative basal area - An estimate of basal area for trees, such as produced by the Bitterlich sampling tech- 

 nique. 



Relief - The change in elevation of a land surface between two points; collectively, the configuration of the 

 earth's surface, including such features as hills and valleys. 



Reproductive adaptation - A peculiarity of the reproductive mechanism of a species that results in it being 

 better fitted to its environment (e.g., prolonged seed dormancy). 



Rhizosphere - The zone of soil in which interactions between living plant roots and microorganisms occur. 



Salic horizon - A layer 6 inches or more thick comprised of secondary soluble salts. 



Salonhids - Soils of arid regions with a salic horizon within 30 inches of the surface and saturated within 

 40 inches for one month or more in most years; common in playas of the Southwest. 



72 



