三峡库区澎溪河消落带植物群落分布格局及生境影响

三峡消落带是一条特殊的水—陆交错带,其生境的特殊性及对整个三峡库区的影响逐渐成为地学、环境科学、生态学等学科的研究热点。植被是消落带各项生态功能的载体。然而,三峡水库的运行使消落带原有植被遭到破坏。通过对澎溪河消落带植物群落及其生境的实地调查,采用双向指示种法(TWINSPAN)划分植物群落类型,并结合方差分解和CCA排序法研究4类生境影响因素组14个生境影响因子与植物群落空间分布的关系,探讨生境对消落带植物群落组成、结构及多样性的影响。结果表明:(1)消落带植物群落包括5种类型:狗牙根+雀稗群落、狗尾草+狗牙根群落、黄荆群落、白茅+鬼针草群落、苔草群落;(2)CCA排序中,第1排序轴对消落带植被空间变化的累计解释量为6.83%,占生境条件总解释量的44.73%,能很好地解释消落带植物群落与生境的相互关系,植物群落类型沿排序轴呈梯度分布;(3)土壤是影响消落带植被空间分布格局的主要影响因素组,各影响因素组间交互作用明显。淹水时间、海拔、土壤含水量是植物群落空间分布的主要影响因子,解释量分别为5.3%、3.0%、2.9%;(4)4类影响因素组共解释消落带植物群落空间格局变化的14.6%,未解释部分所占比例较大,可能是由于消落带内生境条件复杂,影响其群落组成及空间分布的潜在因素较多,如各种土地利用政策、人类活动干扰及景观组成等因素也可能对消落带植物群落构成有影响。研究消落带植物空间分布及其与生境的关系,以期为科学认识消落带、保护水库环境提供依据。

Spatial distribution pattern of plant community and habitat impact analysis of the drawdown zone of Pengxi River in the Three Gorges Reservoir

Riparian vegetation has important ecological functions in protecting the water quality, stabilizing the bank and maintaining the habitats connectivity. The impoundment of the Three Gorges Reservoir has destroyed the original riparian vegetation and potentially threatens the reservoir ecosystem''s health and stability in the Three Gorges Reservoir. This research study explored the riparian vegetation community of the newly formed drawdown zone of the Three Gorges Reservoir and the relationship between the spatial distribution patterns of plant community and the habitat influences. A field survey was carried out from August to September 2015, and 93 plant quadrats were investigated. At the same time, 14 factors including three topographic (slope, exposure, and elevation), three hydrology (flooding time, frequency, and depth), seven soil (pH, moisture content, organic matter, available nitrogen, phosphorus, and potassium, and slow-release potassium) and one historical land use (historical land use) factor were measured. These habitat factors were classified into four groups:topographic, hydrology, soil, and historical land use factor groups. The community types were identified using a two way indicator species analysis (TWINSPAN). Additionally, the effects of the four habitat factor groups and their interaction on the total variation of drawdown vegetation were partitioned using variance decomposition. The effects of 14 habitat factors on the drawdown plant communities were analyzed using the canonical correspondence analysis (CCA). The main results were as follows. (1) The drawdown plant communities were classified into five types, which were a Cynodon dactylon plus Paspalum thunbergii, Setaria viridis plus Cynodon dactylon, Vitex negundo, Imperata cylindrica plus Bidens pilosa, and Carex tristachya communities. (2) The results of the CCA indicated that drawdown vegetation and habitat factors had a significant correlation. The cumulative interpretation of the first ordination axis on vegetation spatial variation was 6.83%, accounting for 44.73% of the total interpretation of the habitat. Five types of plant communities were distributed along the first ordination axis following the altitude gradient. (3) The results of the variance decomposition showed that the soil factors group had only a 10.1% contribution. It played a major role in the spatial distribution of the drawdown plant community among the four habitat factor groups. There was a significant interaction between the four habitat factor groups. The CCA also showed that the habitat factors of flooding time, elevation, and soil moisture content played a dominant role in the spatial distribution of the drawdown plant community and their contribution were 5.3%, 3.0%, and 2.9% respectively. (4) Our results demonstrated that the explanatory power of all four habitat factor groups was low (14.6%). This may be because the drawdown zone is a newly established, complex ecotone, where habitats and landscapes are highly heterogeneous. The unexplained portion may come from the influence of anthropogenic activity, various disturbances, and large-scale landscape context.