tailieunhanh - Báo cáo lâm nghiêp: "Thinning Forestry control of conifer plantations in Great Britain"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Thinning Forestry control of conifer plantations in Great Britain. | Ann. Sci. For. 1987 44 1 25-34 Thinning control of conifer plantations in Great Britain . ROLLINSON Forestry Commission Research Station Alice Holt Lodge Farnham Surrey UK Summary Thinning practice in Great Britain has been influenced in recent years by the growing recognition of the threat of wind damage to plantations and by the decline in the real price of small roundwood. Current thinning practice in the Forestry Commission is based on assessments of the likelihood of wind damage and the costs and revenues of thinning operations. Where the risk of wind damage is high no thinning is the preferred option where the risk of wind damage is moderate thinning is likely to be done at conventional first thinning ages and where the risk of wind damage is low thinning may be delayed by 5 to 10 years. Economic appraisals are carried out to determine whether or not stands should be thinned and if so how. The various elements which comprise a thinning regime are described that is the thinning type the intensity of thinning the thinning cycle the thinning yield and the timing of thinning. The control system used when marking a stand for thinning is described The system is based on control of the volume removed in a thinning operation and relies on field assessments of basal area stocking and the volume marked as thinnings. Introduction Since the 1940s a major programme of afforestation has taken place in Great Britain leading to the creation of extensive areas of even-aged plantations on upland sites in the exposed north and west of the country. There are about 1 321 000 hectares of mainly coniferous high forest of which 85 per cent is less than 40 years of age Forestry Commission 1984 . Some 62 per cent of this area is managed by the Forestry Commission. As a result of the type of sites available for planting and the changes in choice of species over the years the major coniferous species is Sitka spruce Picea sitchensis Bong. Carr. with 526 000 hectares followed by .