不同类型人类活动干扰对河岸带外来植物群落的影响——以北京永定河为例

强烈的人类活动对自然生境的扰动促进了外来植物侵入河岸带,但不同类型的人类活动干扰对外来植物的影响有所不同。按照不同人类活动干扰类型设置了山峡段、平原段和城市段,通过比较河段间河岸带外来植物群落特征的差异,探讨不同人类活动干扰类型对河岸带外来植物群落的影响。结果表明:(1)永定河河岸带共有维管束植物27科72属101种,外来植物13科28属29种。外来种比例高达28.7%,其中82.4%的国外外来种来自美洲和亚洲。(2)不同河段间的外来植物群落的物种构成和优势度呈现出显著性差异。外来种比例由山峡段的20.9%,上升至平原段和城市段的30.2%和25.5%;而优势度由12.1%,分别上升至13.4%和17.5%。(3)不同河段间的外来植物群落生活型结构有显著性差异。多年生草本植物在山峡段比例最高,达到66.7%,在平原段和城市段较低,分别为46.2%和30.8%;而一年生草本植物在城市段比例最高,达到69.2%,在平原段和山峡段较低,分别为53.8%和33.3%。(4)平原段属于农业干扰类型,其河岸带外来植物主要以农业类杂草为主,如禾本科的假稻(Leersia japonica)和菊科的钻叶紫菀(Aster subulatu);城市段是城市干扰类型,外来植物中入侵种比例和优势度较高,典型入侵种为反枝苋(Amaranthus retroflexus)和牛筋草(Eleusine indica)等。北京永定河不同河段河岸带外来植物的种类构成特点,反映了河岸带外来植物受快速城市化、农业活动等不同人类活动干扰的影响呈逐渐扩大的趋势。

Community characteristics of riparian alien plants influenced by different types of human disturbance: A case study of Yongding River, Beijing

Riparian zones are highly modified by frequent and intense human disturbances worldwide. Human-mediated disturbances often occur in concert with the proliferation of alien plants in the riparian zone, although their effect on alien riparian plants may differ among disturbance types (agriculture, urbanization). However, few studies in China have attempted to detect these effects on alien plants in riparian zone. The objectives of this study are (1) to compare the characteristics of alien herbal plant communities in different sections of a river (mountain section, agricultural section, and urban section) and (2) to explain the differences in alien plant communities that are caused by different types of disturbances (agriculture and urbanization).This study was conducted in 2009 in the riparian zone of the Yongding River in Beijing. The river stretches were categorized into three river sections based on the human-mediated disturbance types in that stretch of the river: mountain section (natural section without disturbance), plain section (agricultural disturbance), and urban section (urbanization disturbance). Using the transect method, 11 study sites were set up in this three river sections. The results show that the vascular herbal flora of the study area comprises 101 species from 72 genera and 27 families, including 29 alien plant species from 28 genera and 13 families. Alien species represent 28.7% of the total herbal flora, of which 82.4% originated from America and Asia. The species composition and dominance index of alien riparian plant communities change significantly among the three river sections. The percentage of alien species increases from 20.9% in the mountain section to 30.2% and 25.5% in the plain and urban river sections, respectively; the dominance index increases significantly from 12.1% to 13.4% and 17.5% in the plain and urban river sections, respectively. The composition of alien riparian plant communities inferred from the life cycle of the plants also shows significant difference among the three river sections. Perennial species are the most abundant in the mountain section (66.7%), while they are represented by 46.2% and 30.8% in the plain and urban sections, respectively. In contrast, the highest percentage of annual species is found in the urban section (69.2%) followed by the plain section (53.8%) and the mountain section (33.3%). The plain section is greatly affected by agriculture, where the alien riparian plants are mainly dominated by agricultural weeds such as Leersia japonica and Aster subulatus. The urban section is strongly influenced by the disturbance from rapid urbanization, in which the percentage and dominance index of invasive plant species are high. The typical invasive plants are Amaranthus retroflexus and Eleusine indica. These results indicate that the species composition of alien riparian plants differs among river sections and they are affected by different types of human-mediated disturbance (agriculture, urbanization). Our results also indicate that alien riparian plants may become predominant and spread further in the riparian zone due to human activities such as rapid urbanization and agriculture.