| The spruce budworm has had significant impact on Michigan's forests. Except for aerial surveys the nature and extent of the impact is poorly documented. In 1978, a 5-year study was initiated in Michigan's Upper Peninsula to quantify spruce budworm impact. An original adaptation of multi-stage cluster sampling was designed.; The design, called a 3-stage cluster sampling scheme, was used to establish the Michigan Impact Plot System within the Ottawa and Hiawatha National Forests. The primary sampling unit (PSU) was a forest compartment, the secondary sampling unit (SSU) was a spruce-fir stand, and the tertiary sampling unit (TSU) was one of three concentric circular plots of 0.02, 0.04, or 0.08 ha established around a common center. All three concentric circular plots were collectively called a composite ground sampling unit (CGSU). Formulas were developed to estimate means, totals, and associate standard errors for various parameters. Data from a cluster of TSU's, SSU's, or PSU's described a stand, compartment, forest district or national forest, respectively.; Total dead volume, live volume per hectare, average percent mortality, mean defoliation ranking, and average top-kill ratio were cluster sampling estimates. Incidence of spruce budworm feeding on saplings and reproduction was depicted by level of feeding. Statistics from an annual inventory of 108 CGSU's in 1978, and 136 CGSU's in 1979 and 1980 provide a more precise estimate of the impact of the spruce budworm in Michigan's Upper Peninsula than has been available to date. Allowable error was usually less than 50% and for certain national forest statistics was 4% of the estimated mean or total. Information derived from my impact data will be more credible and have broader application because my sampling design met prescribed location and allocation goals, reduced sampling bias, and because my sample size was sufficient. |
