Sample size (n) can be determined using a statistical approach that considers the variability of the population and our requirements for precision. The formula to determine the number of samples needed to meet these statistical criteria is
Standing crop is the total above-ground plant biomass on the site at a particular point in time. Standing crop includes current year's production together with that produced in previous years. Standing crop at a site fluctuates within and among years, depending on seasonal conditions and utilization by grazing animals.
Transects are specially shaped sample units having a length dimension that greatly exceeds the width, so that it extends in a continuous manner across the vegetation. Transects are the sample unit of choice when sampling involves larger plants, such as shrubs or trees, because it allows a larger area to be systematically sampled by proceeding along its elongated axis.
Stratified sampling involves dividing the site into sections that are more homogenous than the entire area. Boundaries of the sections should be based on factors that are readily identified and mapped, such as different vegetation types, soil types, topography, range sites, range condition classes or utilization levels.