The present paper deals with the minimum width of the isolation strip around yield plots against small openings such as small fields, roads and power lines. In 12 stands, also bordered by a narrow ditch, and located in the south of Finland, the growing stock was studied in 2-metre ide strips for a distance of 30 metres from the stand edge. The results are presented by stand grups given in the set-up an p. 320. The stripwise study of cubic volumes (Fig. 1, p. 324) provided no major conclusions. On the basis of analysis of variance it appeared that the mean diameters of the 2 outermost strips were at least significantly differnent from those of strip 4-15. As a rule, the mean diameter of strip 3 was also found to be somewhat greater than those of the inner strips, but the difference was not statistically significant (Fig. 2, p. 324). When studying the basal area growth per tree of each strip during the past 20-year period (Fig. 3, p. 325) it was also detected that on the strip 1, 2 and 3 the growing conditions of trees deviate significantly from those to be encountered an strips 4-15. It was further found (Fig. 4, p. 325) that the unevenaged stands give quite similar results. The small opening does not significantly affect the mean height of the border trees (Fig. 5, p. 326). On the basis of the above results it can be concluded that the isolation strip to be left against small openings now in question should be, in general, at least 6m, wide. This is particularly true of pine and birch stands while in dense planted spruce stands the isolation strip may be somewhat narrower but not lenn than 4m. The present material does not yield direct information on the isolation strip requirements of subplots of sample plot series. However, it is rather apparent that the effect of a neighboring plot, even if under different treatment, does not reach as far as that of the small openings.
