Efficiency of different quadrat sizes and shapes for sampling standing crop

Abstract

Efficient sampling of standing crop is necessary to avoid unreasonable lays of time in the field. The objective of this study was to determine efficiency of different size and shape quadrats for sampling standing crop of total herbage and individual species. Three blocks 1.2 X 12 m were divided into 160 basic units using 30 X 30-cm quadrats. Basic units were combined into 18 size/shape combinations of quadrats. Current year standing crop was clipped in each basic unit into categories of sand bluestem (Andropogon hallii Hack.), prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.], hairy grama (Bouteloua hirsuta Lag.), little bluestem [Schizachyrium scoparium Michx.) Nash], and other herbage. Variance was used to determine sample number necessary to accurately and precisely estimate standing crop. Sample number was then used in conjunction with movement time between quadrats and clipping time to determine total field time as a measure of overall efficiency. Increasing quadrat size accounted for 68% or more of the observed decrease in variance. Long, narrow rectangles were more efficient for reducing variances of prairie sandreed and hairy grama, but shape had little effect on variances of sand bluestem, little bluestem, and total herbage. Groups of quadrats were similar in total field time with no "best" quadrat identified for any of the vegetation categories. Larger quadrats than those reported in the literature were found to be more efficient as a result of including movement time in the optimization procedures. Large amounts of total field time were required to efficiently estimate standing crop of little bluestem, which may require that alternative sampling methods be devised or used to estimate standing crop of this species and others with similar distribution patterns.