Production of Coastal Louisiana Marsh Plants Calculated from Phenometric Techniques

Production and mortality of six marsh macrophytes were measured in Louisiana, USA using phenometric methods. The Williams—Murdoch technique estimates annual production from measurements of individual culm height, mass, growth, and longevity. Annual mortality was estimated from bimonthly field measurements of culm height, mass, and death rate as a function of height, and density. Annual production estimates averaged 1.8 times higher than annual mortality estimates although in a steady—state system the rates should be about equal. A probable and correctable reason for the discrepancy is discussed. These estimates are higher than those calculated from Smalley's method but lower than those obtained from the Wiegert—Evans paired—plot technique. The validity of various techniques are applied to wetlands is discussed.