濒危植物太白红杉种群年龄结构及其时间序列预测分析

Age structure and time sequence prediction of populations of an endangered plant, Larix potaninii var. chinensis

为了阐明太白红杉(Larix potaninii var.chinensis)种群的年龄结构和未来发展趋势,合理保护现有资源,在太白山地区调查了 29个样地(10 m×10m),对处于不同生境的 5个种群的年龄结构、静态生命表和时间序列预测进行了分析。种群年龄结构分析表明,各种群个体数量主要集中于Ⅲ、Ⅳ、Ⅴ、Ⅵ、Ⅶ龄级(个体数量比重占68.64％),幼、老龄个体数量较少。受所处生境条件影响,不同种群年龄结构特点不同:海拔较低的种群(B)由于水热条件适宜,林内有林窗出现,幼龄级个体数相对丰富;而其他种群由于幼龄个体严重缺乏,衰退趋势明显。太白红杉不同种群生命表和存活曲线的分析表明,尽管所处的生境差异较大,但存活曲线基本属于Deevey Ⅲ型,种群偏离典型存活曲线的程度与幼苗缺乏程度有关,一般V-Ⅸ龄级死亡率较高。时间序列分析表明,在未来20、60、100和200年中,各太白红杉种群均会呈现老龄级株数先增加后减少的趋势,种群稳定性维持困难。太白红杉种群年龄结构和动态趋势与银杉(Cathaya argyrophylla)等其他濒危植物比较,导致种群衰退的原因相似:在郁闭的林下种子萌芽和幼苗生长困难。应该利用太白红杉喜光、耐旱和中老年个体产种量丰富的特性,对现有太白红杉林分实行就地保护,合理抚育管理。低海拔地区。

The Taibai larch, Larix potaninii var. chinensis, is an endangered plant only found in the Qin- ling Mountains in China. It is densely distributed on Mount Taibai and plays an important role in environ- mental protection in the high altitude zone. In order to characterize the age structure and dynamics of the L. potaninii var. chinensis population so as to better conserve its resources, 29 plots (10 m×10 m) were investigated on Mount Taibai. The analysis of the age structure of five populations of L. potaninii var. chinensis showed that most individuals (68.6%) were concentrated in the 60 - 140 year age classes. Younger and older individuals were dramatically few. Because of different environmental conditions, dof- ferent populations developed their own characteristic age structure. The population in L. potaninii var. chinensis - Abies fargesii - Lonicera hylocomium - moss association showed a stable development tenden- cy. However, another four populations in L. potaninii var. chinensis - A. fargesii - Betula utilis var. sinensis - Rhododendron clementinae association, L. potaninii var. chinensis - Rhododendron clementinae - Lonicera hylocomium - moss association, L. potaninii var. chinensis - Rhododendron capitatum - Juni- perus pingii var. wilsonii - Carex sp. association and L. potaninii var. chinensis - Rhododendron purdomii - R. capitatum association all showed obvious declining tendencies. The analysis of life tables and sur- vival curves showed that even under different environmental conditions, survival curves of L. potaninii var. chinensis populations belonged to Deevey type Ⅲ, and death peaks of different populations were the in period of 100 - 180 years old. Time sequence prediction models for different populations after 20, 60, 100, 200 years indicated that the numbers of old individuals would increase in the beginning and finally decrease, giving rise to difficulties for maintenance of these populations. The age structure and dynamic trends of L. potaninii var. chinensis populations were similar to those of other endangered species in Chi- na, such as Cathaya argyrophylla. The key cause for population decline was that shade in the forest ob- structed germination and seedling growth. In situ conservation should be strengthened in future, especial- ly for middle and old individuals with reproductive ability. The heliophytic and xerophytic characteristics of L. potaninii var. chinensis should be considered and special counter-measures for fostering the species should be made according to these biological characteristics and habitats. In the lower altitudes, non-tar- get species in the tree layer and some shrub species should be thinned. In higher altitude areas, actions for fostering forest, such as cutting shrubs, clearing herbs, etc. should be taken, so as to create the envi- ronmental condition for development of young seedlings of L. potaninii var. chinensis.