| Abstrakt: |
[Objective] To reveal the long-term effects of site and planting density on stand timber assortment structure of Chinese fir (Cunninghamia lanceolata) plantations in south subtropical area, China. [Method] Based on positioning observation data of 36-years-old Chinese fir plantations at four site index classes in Daqingshan, Guangxi, including five planting densities of A (1 667 trees·hm−2), B (3 333 trees·hm−2), C (5 000 trees·hm−2), D (6 667 trees·hm−2), and E (10 000 trees·hm−2), the dynamic changes of stand timber assortment structure were analyzed. [Result] The number of trees and volume proportions of small diameter wood (SW) increased with age at the beginning, and decreased with age after the peak points. The lower the planting density and the higher the site index were, the faster the decline became. The number of trees and volume proportions of medium and large diameter wood increased with age. The lower the planting density and the higher the site index were, the faster the proportions increased. The volume proportion of stand medium diameter wood (MW) at density D or below and 18-site-index class was about 50% at the age of 28. The volume proportion of stand large diameter timber (LT) at density A and 18-site-index class was about 50% at the age of 36. At 16-site-index class, the ratio of stand MW volume at middle and low planting density was over 45%, and the ratio of density C stand was about 48% which was the highest, and the volume proportion of LT at density A stand was over 26% at the age of 36. At 14-site-index class, the volume proportion of MW at density A stand was 44% at the age of 24, the volume proportion of SW of density A, B, and D was 83%, 76% and 69% at the age of 12, 18 and 24, respectively. At 10-site-index class, the volume proportion of SW at density C and E stand was 71% and 61% at the age of 36, respectively. [Conclusion] The timber assortment formation of Chinese fir plantation is closely related to site, density and age, the site quality plays a decisive role, while the planting density can also be a key limiting factor in cultivating high specification timber assortments. Lower initial planting density and higher site index are more conducive to the formation of MW and LT. In south subtropical area of China, the site of 10-indexclass is to be fit only for cultivating SW and small bar timber. The site of 14-index-class is suitable for cultivating MW and SW. If MW is taken as the first target, the planting density should be low. The site of 16-index-class is suitable for cultivating MW, LT can also be cultivated if the period is long enough, but the planting density should not exceed 1667 trees per hectare. The site of 18-index-class has great production potential of MW, cultivating LT is a better choice, but the planting density should be controlled at density A, rotation period should not be less than 36 years. [ABSTRACT FROM AUTHOR] |
