Föryngringsresultat och beräknad virkesproduktion i naturligt föryngrade tallbestånd i Västerbotten under mitten av 1990-talet

Sammanfattning: According to the Board of Forestry, in Västerbotten, many natural regenerations of Scots pine (Pinus sylvestris) carried out on privately owned forest in the middle of 1990 in Västerbotten have rendered a bad regeneration outcome and will provide a low future forest production. The Board of Forestry believes that the negative result can be explained by the fact that the regeneration has been carried out in wrong locations and that scarification failed to work as planned. In order for an accepted rate of regeneration the guidelines of the Forrest Act require, not less than 10 years after final cutting at natural regeneration, that there should be at least 1300 (site indices 16 m) - 1700 (site indices 20 m) main crop stems per hectare. Main crop stems are defined as stems according to the place of growth and appropriate tree type, in addition with regard to quality, stage of development and damage risk have a prospect of succeeding. In addition main crop stems should be separated by surface so that the proportion sample plots with 3 meters radius, and lack main crop stems, are not more than 10 % of site indices 14 meters or higher. The purpose of this thesis is to describe the outcome of the regeneration and to estimate future production in 20 objects regenerated with natural regeneration below seed trees that took place in Lycksele and Umeå districts between 1992 and 1996. In each district 10 objects were randomly chosen. The site indices for the objects were between 16 m and 20 m. Each studied object had 40 sample plots with an area of 10 m². On each sample plot the number of stems, main crop stems and the height of the main crop stems were registered. In each object registrations of altitude, soil condition, type of vegetation and scarification was carried out. To calculate the future forest production HUGIN: s forest models were used. There were two alternatives for calculation, one with pre-commercial thinning up to registrated number of main plants, and one without pre-commercial thinning. The calculations were set to a future thinning phase occuring when the objects had an average height of approximately 11 meters. The location of the objects regarding altitude, soil condition and vegetation was in line with custom recommendations for natural regeneration. Merely twelve of the objects reached acceptable levels of regeneration according to the Forest Act § 6. Objects in Lycksele district had a better regeneration result than objects in Umeå district. Scarified objects had more stems and main crop steams per hectare than object were scarification did not take place, but this correlation could not be statistically secured. The calculated production in the objects varied between 50 and 270 m³sk per hectare depending on the regeneration result and calculation method. Objects with more than 2500 main crop stems per hectare was calculated to produce three times more volume before thinning then objects with less than 1000 main crop stems per hectare. If pre-commercial thinning was excluded in the objects that did not meet the standards according to the Forest Act, they would estimate to produce more volume prior to thinning and give more merchantable timber than approved objects with pre-commercial thinning. However calculations without pre-commercial thinning took less consideration to the trees actual positioning than calculations with pre-commercial thinning so the future volume without pre-commersila thinning could be expected to be lower than the estimated values. According to this study the location of the objects was in line with general recommendations fore natural regenerations below seed trees, despite the fact that eight of the objects did not meet the standards according to the Forest Act. Scarification and help planting was not carried out in several objects in Umeå district which could explain the worse regeneration result. The calculation shows that the future production in natural regeneration, with site indices between 16 m and 20 m in Umeå and Lycksele districts, could be expected to differ considerably between objects, primarily because of variations in regeneration result. The calculations also shows that the future production potential could be larger if the regeneration result is not only based on the amount of plants that fulfil the definition of main crop stems, but also is based on the total amount of plants in the regeneration.