Wetland seed abundance estimates influenced by soil core volume
Soil core sampling is commonly used to estimate moist-soil seed abundance when assessing waterfowl habitat and population carrying capacity. Several studies have evaluated the limitations and sources of bias associated with soil core sampling, but few have examined how variable sample volumes can influence estimates of seed abundance. We measured the soil volume of 1,128 soil cores collected from managed seasonal wetlands and tidal marshes to determine if seed abundance was correlated with the volume of soil sampled. We collected soil cores using a standard (6 cm diameter, 5 cm deep) soil coring device with external flanges to control sampling depth. We found that the actual soil volume sampled was highly variable (45 ml to 560 ml). Mean soil volume (215.6 ml) was 53% greater than the targeted soil volume based on the dimensions of the coring device (141.4 ml). Moreover, total seed mass was positively correlated with soil volume sampled in managed wetlands but not in tidal marshes. Using a linear model, we found managed wetland samples contained an additional 33.2 kg/ha of total seeds due to the extra 74.2 ml of soil collected per sample on average. Total seed abundance in managed wetlands was estimated to be 19.6% greater due to the oversampling of soil. Estimates of seed abundance in moist-soil wetlands derived from soil core samples may be improved by considering the variability in the actual soil core volumes sampled using standard sampling tools.