退化中的长白山西坡灌木苔原优势种分布差异

长白山苔原带植被正在发生显著变化,灌木苔原中灌木植物分布范围萎缩,重要值下降。通过样方调查数据,分析灌木苔原中优势种的变化,灌木分布格局和灌木群落结构特征沿海拔的差异,旨在揭示长白山灌木苔原退化的区域差异,为明确其退化机理提供基础数据。研究表明:(1)长白山西坡灌木苔原退化严重,多种草本植物已经侵入,并成为优势种。目前7个优势种中灌木仅占2席,草本植物占据5席,与1979年的样方调查结果相比灌木优势种的数量和地位都明显下降。7个优势种均为聚集分布,各优势种分布呈现斑块化、分离化,统一的灌木苔原面临解体;大部分灌木苔原群落中,出现了草本层,苔原带下部灌木苔原中草本层高于灌木层,物种组成和群落形态接近草木苔原。(2)灌木在各海拔均仍有广泛分布,但其空间分布格局明显不同。在海拔2300m以下,灌木的分布产生较强的聚集现象,特别是在海拔2100m以下这种聚集分布现象更为突出;在海拔2300m以上灌木的聚集程度较弱。(3)长白山西坡灌木苔原退化的区域分异明显,在海拔2100m以下灌木苔原退化严重,成为草-灌苔原;在海拔2100—2300m之间,灌木苔原退化较严重,成为灌-草苔原;在海拔2300m以上,退化较轻,仍为灌木苔原。由此推断,长白山西坡灌木苔原的退化机理应包括两个方面:草本植物入侵,种间竞争导致灌木退化,以及环境变化导致灌木退化,二者皆可能是全球气候变化的结果。

Distribution variations of dominant plant species in degraded shrub tundra on the western slope of the Changbai Mountains

Tundra vegetation of the Changbai Mountains is undergoing significant changes. In the alpine tundra on the western slopes of the mountain, the area of distribution of shrubs is shrinking and the importance of shrubs as dominant plant species is reducing significantly. This study analyzed changes of dominant plant species in the shrub tundra, distribution pattern variations of shrubs and characteristics of shrub community structure at different elevations using plot survey data, revealed regional differentiation of degradation in shrub tundra and the degradation mechanisms of shrub communities. The results showed the following: (1) The shrub community in the alpine tundra on the western slopes has been severely degraded. Various herbs have invaded the area and became the dominant species. Five herbs and two shrub species were the dominant species of alpine tundra, which indicated a decrease in the number and importance value of dominant shrub species compared to the results of the survey conducted in 1979. The aggregated distribution was the dominant pattern of distribution of the seven dominant species, whereas the distribution of each dominant species occurred in separated patches; the shrub tundra faced fragmentation. In shrub communities of alpine tundra, herbs appeared and gradually became dominant. The herbs were taller than the shrubs in alpine tundra at lower elevations, and the species composition and community form were nearing those of the herb-shrub tundra. (2) Shrubs were widely distributed at different elevations, but their spatial distribution patterns were distinct. Below 2300 m a.s.l., the distribution of shrubs appeared aggregated, especially at elevations below 2100 m a.s.l. The shrubs did not aggregate above 2300 m a.s.l. (3) Regional differentiation of the degraded alpine tundra on the western slopes was significant. Below 2100 m a.s.l., the number of herbs was more abundant than that of shrubs, and the coverage and height of the shrubs were decreased; so the degradation is the most serious in this region, which developed into herb-shrub tundra. Between 2100 and 2300 m a.s.l., the degradation was significant, but the number of shrubs were more abundant than that of herbs; this region developed into shrub-herb tundra. Above 2300 m a.s.l., the degradation of shrubs was not significant and shrub tundra was preserved. It can be inferred that the degradation mechanism of the shrub tundra includes two aspects: herb invasion of the shrub tundra, resulting in interspecific competition, and environmental changes of tundra zone, which could be attributed to global climate change.