Agenda - Environmental Policy Board - 07/19/2021

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54 J.C. SPARKS, R.E. MASTERS and M.E. PAYTON method can also be used to sample all stems in an area regardless of size, but produced less accurate estimates than those of the FRP- AC or FRP-HA methods when samp-ling small stems. However, the QUAD provided more accurate estimates of larger stems than did both FRP methods. The QUAD tended to be less time -efficient than the FRP methods and required the use of a transit and tape measure for accurate plot layout or a large sampling quadrat, which can be cumbersome to transport and set up in dense stands. The QUAD method requires considerable care so that stems are not counted twice. Although the VRP method was one of the fastest methods, its use should be limited to primarily larger stems with a DBH >11.43 cm. The VRP method produced poor and wide ranging accuracies on smaller stems (<11.43 cm), overestimating dense stands and underestimating low -density stands. The VRP also tended to underestimate overall stem density of stems >11.43 cm, but estimates were a consistent percent dif- ference across all stand densities and may be reduced if additional samples were taken. The BT produced poor estimates on small stems, but relatively accurate esti- mates on larger stems. Although it can be used to sample all stems regardless of size, this method was not very time -efficient, primarily because transects must be set up and measured before sampling can begin. This method would be best suited to long transects, with the aid of a compass and a device to measure distance traveled. The BT method may be best applied in transition zones or gradients where the vegetation changes in composition and density (6). The PCQ method was quite time - efficient, but was applied only to larger stems. The PCQ method tended to under- estimate actual stem density in all stands, but like the VRP, the PCQ method also maintained a consistent percent difference in observed versus estimated stem densities across all stands regardless of overall stem density. That distance techniques may give biased estimates, depending on tree spatial distributions, is an inherent disadvantage. Shape: FRPs with a circular shape tended to produce the most accurate results on smaller stems (2.54 to 11.42 cm), especially when applied in dense, evenly distributed stands. This can be attributed to the small perimeter to area ratio in a circle; therefore, an observer is less likely to have to make a decision to tally a stem or not because it intersects the plot (17). Also, the rotating radius of the plot allows an observer to ensure all stems are tallied and are only tallied once. When using a large quadrat (10 m x 10 m) it is easy to miss stems or to tally them twice (6,18). The FRP methods or circular -plot sampling methods are quick and simple to apply in areas with low to moderate density of stems or areas with low vegetation, but become awkward in dense, shrubby communities (6,18). Smaller FRP or square -plot methods can be used in stands with dense vegetation (18). Size: It is essential for quadrat size to be adapted to the characteristics of the vege- tation being sampled (18). The greater the species diversity and the more hetero- geneous life forms found in a community, the larger the quadrat size needed to adequately characterize the community (18). Regardless of shape, perimeter to area ratios decrease with an increase in quadrat size (17). Based on the diversity found in many forested communities and on perimeter to area ratios, larger circular plots would be most appropriate (17). CONCLUSIONS It is important for managers to know the general characteristics of the stand they are attempting to sample because no single method is efficient for sampling all stem sizes and densities. Sample procedures provide only an estimate, and this estimate may be smaller or greater than actual stem density depending on the sample method applied and stand density. Methods should be chosen that reflect unbiased estimates of density given various stand conditions and distributions. Circular and fixed area methods, such as the FRP-AC and FRP-HA, were the most Proc. Okla. Acad. Sci. 82:49-56(2002)