EFFICIENCY OF DIFFERENT QUADRAT SIZES AND SHAPES FOR SAMPLING STANDING CROP

Efficient sampling of standing crop is necessary to avoid unreasonable outlays of time in the field. The objective of this study was to dete rmine efficiency of different size and shape quadrats for sampling sta nding 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. Bas ic units were combined into 18 size/shape combinations of quadrats. Cu rrent year standing crop was clipped in each basic unit into categorie s of sand bluestem (Andropogon hallii Hack.), prairie sandreed [Calamo vilfa 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 acc urately and precisely estimate standing crop. Sample number was then u sed in conjunction with movement time between quadrats and clipping ti me to determine total field time as a measure of overall efficiency. I ncreasing quadrat size accounted for 68% or more of the observed decre ase in variance. Long, narrow rectangles were more efficient for reduc ing variances of prairie sandreed and hairy grama, but shape had littl e effect on variances of sand bluestem, little bluestem, and total her bage. Groups of quadrats were similar in total field time with no ''be st'' quadrat identified for any of the vegetation categories. Larger q uadrats than those reported in the literature were found to be more ef ficient as a result of including movement time in the optimization pro cedures. Large amounts of total field time were required to efficientl y estimate standing crop of little bluestem, which may require that al ternative sampling methods be devised or used to estimate standing cro p of this species and others with similar distribution patterns.