Gallringsprioritering av contortabestånd
Extensive planting of the tree species lodgepole pine (Pinus contorta var. latifolia) during the 1970s and 80s has resulted in large areas now being available for commercial thinning. However, the varying quality of the stands creates a problem. The purpose of this study was to investigate, at the Torsby district of the Stora Enso forest company, how well the present computer records of the stands correspond to reality and determine which stands are, from a qualitative perspective, suited for timber production. Finding variables that indicate better stands would give Stora Enso the possibility of selecting qualitative stands which are more profitable to thin.
The study included 32 stands containing at least 70 % Pinus contorta. Eight survey plots (100m²) were placed in each stand and potential sawtimber trees as well as stem injuries were registered. The registered data at Stora Enso showed low correspondence to the actual measured values. Stand volume and mean height were generally higher than the registered values, and the age of the stands was approximately three years older. Site index (H50, m) in the visited stands was between 18,8 and 23,2 with the mean value 20,7 which was 2,0 meters higher than the registered data.
The stem number (d>5cm) was in average 1588 per hectare. The proportion of potential timber trees (not damaged) was in average 21 %, which corresponds to approximately 330 stems/hectare. Many of the stands were regenerated with seedling containers, which had been sawn with several seeds resulting in multiple seedling containers. This resulted in 8% multiple stems. The average growing stock was 121 m³sk/ha with a mean top height of 12,6 meter. Stands with suitable site conditions (heavier texture) showed less damaged contorta-stems. Field-layers containing cowberries (V. vitis-idaea) and vegetation indicating poorer site conditions were positively correlated with the amount of timber trees. The amount of wrecked and fallen stems increased with increasing altitude. The most common defect on the trees was a bend, generally located at the bottom of the stem. Variations between stands were large and the presence of domestic tree-species with better quality was significant in many stands. The calculation relating to those stands therefore gave a significantly higher rate of timber trees. The qualitatively best stands with a small amount of injured trees were found on poor vegetation types at lower altitudes.