A simple method to predict seed yield in moist-soil habitats

Information on production of moist-soil seeds is necessary to determine resource availability in wetland habitats and evaluate management efforts. Traditional methods (e.g., core sampling and seed-head clipping) are time-consuming and labor-intensive. Methods to estimate seed production using seed-head characteristics tend to be complex and may have limited utility for some moist-soil plants and in some regions. We developed a simple method to evaluate percent cover and seed-head characteristics of 6 common moist-soil plant types in the Central Valley of California. We estimated percent cover (AREA) and seed-producing potential of each plant type (QUALITY) using an ordinal scale for 13 wetland units on private duck clubs. The product of the AREA and QUALITY scores was calculated for each plant type and then summed over all plant types to provide a single index of seed production (Seed Production Index, SPI) for each unit. To evaluate the reliability of this index, we regressed the value of SPI for each unit against estimates of seed production derived by core sampling. The SPI index was correlated with estimates of moist-soil seed biomass (kg/ha) obtained by core sampling (R-adj(2)=0.88, P < 0.0001). To further assess the utility of this method in a field situation, 2 observers estimated SPI independently for 183 wetland units during annual site visits for the California Comprehensive Wetland Habitat Program. Estimates of SPI required < 15 minutes for most wetlands and were repeatable for the 2 observers (intraclass correlation coefficient =0.79, P < 0.0001). We suggest that this technique will provide managers with a simple method to estimate seed production in moist-soil wetlands, track temporal changes in food abundance within wetlands and across landscapes, estimate wetland carrying capacity, and evaluate management actions with minimal resource investment.