西藏亚高山暗针叶林结构的研究

<正>一、西藏亚高山暗针叶林的组成结构多为单优结构和云杉、冷杉的同型复合结构。在分布带内,阴坡下段多云杉纯林,上段多冷杉纯林;阳坡下段多云,冷杉与高山栎混交林,上段多冷杉,云杉与大圆柏混交林,最上段多方枝柏纯林。 二、云杉林和冷杉林均为复层林。圆柏纯林多为单层林。亚高山暗针叶林的林下层片较完整,并有1—2个层片发育良好而稳定。阴坡的下段多有发育极好的苔藓层,上段多亚乔木状的杜鹃下木层;阳坡下段多由箭竹组成的下木层。草木层一般不发达,层外植物发育良好。 三、亚高山暗针叶林分立木的年龄跨幅大,主林层的立木在200—300年以上,林下立木多在100年左右。暗针叶林立木的生长持续期长,200—300年以上仍继续生长,而林下立木有潜在的生长优势。 四、亚高山暗针叶林的立木径级分布幅度宽,树高差异大。在立地条件好的林分中,立木胸径多在60—100厘米以上,树高40—50米以上,最高可达70余米。林分中高大立木的比例和林分蓄积量的变化规律是:湿润区>半湿润区,阴坡>阳坡,低海拔>高海拔(分布区内),云杉林>冷杉林>方枝柏林,藓类林型>灌木林型>箭竹林型>杜鹃林型>草本林型>高山栎林型。 五、鉴于亚高山暗针叶林的结构特点,建议采伐时一律实引择伐,严禁皆伐,采伐胸径在50厘米以上,年龄在150年以上立木。

A STUDY OF THE CONSTITUTION OF SUBALPINE DARK CONIFEROUS FORESTS IN XIZANG

1, The constitution of subalpine dark coniferous forests in Xizang is chiefly of single superior structure or confluent structure of Picea (Spruce) and Abies (Fir). In regions of distribution, there are more pure forests of Picea in the lower parts of shady slopes, and at the higher altitudes there are more pure forests of Abies. On shiny slopes, there are more forests of mixed Picea, Abies and Ouercus aquifolioides at the lower altitudes, and on the higher parts there are more forests of mixed Abies, Picea and Sabina tibetica, with pure sabina saltuoria forests on top of them.2, The forests of Picea and Abies are all irregular forests and the pure forests of Sabina are more regular forests. The synusiae under the subalpine dark coniferous forests are intact and complete, with l-2 of them well developed. Many well developed Actinothuidium (Mogs) synusiae are found in the lower parts of shady slopes and many underplants of Rhododendron of sub-arboreous are found at the higher altitudes. In the lower parts of shiny slopes, underplants of Sinarundinaria (Chinacane) often occur. Generally, layers of grassland vegetation are undeveloped, but plants out of this story grow well.3, The standing trees of the subalpine dark coniferous forests have a large age-scope, the principal plants being more than 200-300 years old and the urulsrplants about 100 years old. The standing trees of the dark coniferous forests have longevity and continue to grow after an age of 200-300 years, and the trees of under stories even show a potential superiority of growth.4, The trees of the subalpine dark coniferous forests have a wide range of dia-meter grades and the heights of the trees also vary greatly. Where the conditions of locality are good, the trees often have breast height diameters of about 60-100 cm and heights of about 40-50 m, with the tallest ones reaching over 70 m. The patterns of the variations of the tree tallness and the amount of wood stock of the forest are as follows: humid region > semi-humid region; shady slope > shiny slope; low elevation > high elevation (distributed region); Picea forest > Abies forest> osabina saltuoria; Actinothuidium forest types > brush forest types> sinarundinario.