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• short of expending the effort to sample everything, yet would provide an ample number upon <br />which to calculate variance. Within each primary unit, three (3) 2mx50m shrub density <br />transects were randomly located and randomly oriented in the normal fashion. The sampling <br />fraction of the primary units (n/N) was 15/20. The sampling fraction within each primary <br />unit (m/M) was 3/607, that is, within each 15 acre primary unit, there was a potential to <br />have 607 different sample locations, of which three were actually sampled. Variance was <br />calculated in the fashion described in Cochran (1977: expression 10.14) and the Methods <br />section above (terms used in the expression below are defined in the Methods section). <br />1-f 1 1-f2 <br />Vy = S12 + S22 <br />n mn <br />1-(15/20) 1-(3/607) <br />Vy = 19.72 + 29.05 = 0.971 <br />15 3 x 15 <br />• <br />The result of sample adequacy calculation using the above calculated variance (0.971) was that <br />with a sample size of fifteen (the number of primary units), the minimum sample size required <br />(using atwo-tailed t-value with fourteen degrees of freedom: t=1.761) was nine. Thus, the use <br />of a two-stage sampling approach allowed the achievement of sample adequacy with <br />approximately the same number of individual samples as were used in the separately completed <br />one-stage approach (in which sample adequacy was not achieved). <br />The Wadge Pasture shrub density estimated by the mean of single stage sampling was 251 stems <br />per acre. The estimate from 2-stage sampling was 239 stems per acre, well within one <br />standard error of the single stage estimate. <br />Implications of Shrub Density Patterns for Future Plant Community Structure <br />The high variability of Wadge Pasture shrub density data illustrates the fact that shrubs are <br />successfully occupying some sites, while in other sites they are not. Over time, this may result <br />in the presence of distinct shrub communities and herbaceous communities. As this develops, it <br />• <br />25 <br />