Application of secondary production methods to estimates of net aboveground primary production of emergent aquatic macrophytes

Abstract

Four methods commonly used for estimating secondary production of invertebrates were applied to clonal emergent aquatic macrophytes as a means of estimating net annual aboveground production (NAAP). Results from these techniques were then compared with those from two traditional methods of estimating NAAP, the summed shoot maximum and the aboveground maximum biomass methods. The three cohort-based methods (Allen curve, increment summation, and instantaneous growth) yielded higher estimates than aboveground maximum biomass values, but were lower than those of the summed shoot maximum method. However, corrective modifications must be made in all three cohort methods because of continuous emergence of new shoots. The size frequency method for non-cohort populations was used to estimate NAAP of asynchronous emergent macrophytes. This method accounts for new individuals that emerge continuously because production is calculated from the change in numbers and individual biomass between size classes, and not between sampling dates of cohort methods. Therefore, this method is more responsive to continuous growth characteristics of most aquatic plants than the others. The size-frequency method is valid for estimating NAAP, and its use in field estimates may simplify evaluations by reducing labor-intensive sampling of individual shoots from emergence to senescence that are required in other methods.