A Visual Obstruction Method to Estimate Wet Meadow Aboveground Biomass in Marshes of the Boreal Plains, Canada

Vegetation aboveground biomass, a measure of net primary productivity, is an important indicator of ecosystem health. We sought a rapid but accurate, non-destructive alternative to traditional aboveground biomass dry-weight measurement for natural and constructed wetlands in the Boreal Plains Ecoregion of Alberta. We sampled 16 wetlands in 2008 during the period of peak aboveground biomass, using the classic biomass measurement method of clipping, drying, and weighing standing vegetation, as well as a visual obstruction measurement technique called Robel height. Visual obstruction has been used extensively in grassland assessments; however, its use in wet meadow marshes of the Boreal Plains has not previously been reported. To evaluate the effectiveness of visual obstruction in estimating aboveground biomass we used general linear modeling, and found a strong and highly significant relationship (R2 = 0.68, F1.94 = 195.5, p < 0.000001). Power analyses indicated that a nine replicate sample would provide a power of 0.85 to distinguish a visual obstruction difference of 30 cm between two samples. Visual obstruction measurement took considerably less time than clipping, drying, and weighing biomass. Our results indicate that visual obstruction is a rapid, reliable, and effective vegetation bioassessment technique in Boreal Plains wet meadow marshes.