Estimating Net Shoot Production by a Hierarchical Cohort Method of Herbaceous Plants Subject to High Mortality

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Abstract
A new method of measuring mortality and net production of shoots of herbaceous plants is introduced. The method combines an integration of cohort thinning and growth curves with a hierarchical view of plant structure. Mortality of subunits such as branches and leaves, which was ignored by previous cohort production methods, is accounted for by this new approach. Applications to populations of the aquatic plants Myriophyllum spicatum, Potamogeton pectinatus and Vallisneria americana illustrate the technique. The method works well where even-aged cohorts are easily delimited (e.g., by size or by connection via rhizomes to members of other cohorts) and loss of subunits can be verified by censusing branch or leaf scars, or by monitoring changes in the structure of marked shoot systems through the growing season.