Current issue: 55(4)
Under compilation: 55(5)
Permanent sample plots are considered to be the most reliable basis for investigations into structure and development of stands. Such sample plots, established since 1924 in Finland, have been used to study thinnings of varying intensity. These studies are yet too short to give comprehensive conclusions. It is also possible to base the studies on sample plots measured in managed forests and gain in this way information suitable for practical purposes. In this investigation development of stands treated by two different methods, repeated thinnings and repeated selection cutting were studied in pure, even-aged Scots pine (Pinus sylvestris L.) stands in Southern Finland, on three forest types.
The results show that volume increment level of naturally normal stands seem to have been reached easily by stands treated with repeated thinnings. With advancing age, the growing stock of thinned stands fall short from the natural stands. As thinnings have removed primarily the poorest trees, the increment is distributed over trees of a larger size more in thinned than in naturally normal stands.
When intensive cuttings have resulted in a relatively small growing stock, the decrease in volume increment leads to considerable decrease in volume. The size of the tree has no essential effect – within certain limits - on the volume increment of the stand, if the volume removed is similar. However, every intermediate thinning removing largest-sized trees may result in the prolonged rotation. Since the volume increment of an older stand is much smaller than earlier, intermediate thinnings removing largest-sized trees should be avoided if the aim is the greatest volume yield. The growing stock of middle-aged or older stands untreated or treated with slight cuttings only can as a rule be considerably reduced without volume increment declining.
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