伊洛河流域外来草本植物分布格局

外来生物入侵及其防治已经成为生态学关注的重点和热点问题。目前的研究主要集中在外来入侵种上,然而入侵种仅占外来种中很少一部分,因此,研究外来种现有分布格局对研究生物入侵及其防治有重要意义。以伊洛河流域草本植物群落中的外来种为对象,沿河从河源地到入黄河口选取典型样地,在调查流域内草本植物群落中物种组成的基础上选取外来种,并对外来种种类组成及其分布格局进行研究。结果表明:流域内有外来草本植物27种,分属于15科,种类较多的科为菊科、苋科和豆科;引入方式以有意引种为主。流域横向不同生境间,河滩地在水流的养分富集、季节性洪水物理干扰及人为活动扰动作用下,呈现出受外来种分布较多,而受人类活动扰动最强且营养丰富的农田分布较小的分布格局;纵向环境梯度下,上游河源山地属于自然植被区,人为干扰较轻,且受外来种影响较小;中游丘陵区从自然生态系统向农业生态系统的过渡区域,人类活动的扰动有所加强;下游平原农业区,人类活动强烈,区域内以人工生态系统为主,群落物种组成简单但受外来种影响最大,受自然环境和人类活动的双重影响。不同物种在不同生境间差异明显,其中,小蓬草、钻叶紫菀和反枝苋广泛分布于3种生境中。总体上,伊洛河外来草本植物分布格局在自然因素的基础上强烈受人为因素的影响,呈现出从上游到下游逐渐增多的趋势。

Distribution patterns of alien herbs in the Yiluo River basin

With China''s opening up constantly deepens, the threats of invasive alien species unintentionally introduced into China are steadily on the increase to agriculture and forestry production. Eco-safety are further enlarged, however, few studies have examined the distribution patterns and trends of newly detected invasive alien species with respect to taxonomic categorization and origin in this country. Invasive species can impose serious damages to natural ecosystems and pose risks to regional economies and public health. Drainage basin ecosystems are more susceptible to biological invasions than other ecosystems because they are subjected to more frequent human disturbances. Only a small fraction of the alien species current research focuses is invasive species. Therefore, it is crucial to study the alien species in order to comprehend the mechanisms and control of biological invasion. This study was conducted in the Yiluo river basin, straddling Henan and Shaanxi Province (109°43''-113°10''E, 33°39''-34°54''N), ranging from 101 m to 1227 m. The Yiluo River is a major tributary of Yellow River in the south side of the middle reaches. The vegetation in the drainage basin ecosystem of Yiluo River has been heavily impacted by anthropogenic activities. In this research, we focused on the herb communities in different habitats formed by different disturbance types and intensity along different environmental gradients in the drainage area of Yiluo River. A field investigation was conducted in August and September of 2009, to acquire the alien species composition and distribution characteristics in different habitats, from three aspects, longitudinal gradient, transverse gradient and the different alien species among different three types of habitat distribution pattern of the herb species. Using community ecology techniques, 107 plots (20 m×20 m) were sampled. Each plot contains five 1 m×1 m quadrats located at the four corners and the center of the plot. We recorded all the herb species present in the quadrats including the alien species, as well as ecological conditions of the sampling sites. The results of this study show that: there were 27 alien herbaceous species belonging to 15 families in the Yiluo River basin. Compositae, Amaranthaceae and Leguminosae were the three main families, most of which were introduced by human intentionally. The distribution patterns of alien species individuals of occurrence of the alien species in distribution patterns differed significantly among the different habitats, the riparian habitat had the most alien species, while the woodland the farmland habitat had the least. Some of the alien species were widely distributed in all the three habitats, such as Conyza Canadensis, Aster subulatus and Amaranthus retroflexus. We used binomial regression to analysis the distribution patterns of the alien species along the longitudinal environmental gradient. The pattern showed slightly declining curve shaped, the least in the montanic regions in upper reaches of the river, then the hilly regions in middle reaches, and the most in the plains in the lower reaches. The upper reaches were largely covered with natural vegetation of light anthropogenic disturbance and relatively less alien species; therefore the distribution of a species was mainly constrained by its competence and dispersal ability, as well as habitat conditions. The intensively farmed lower reaches were dominated by agricultural ecosystems; species compositions were simple but involved the most alien species as a consequence of intense anthropogenic impact. The hilly transition zone of the middle reaches was under moderate anthropogenic disturbance, covered with mixed communities of natural and artificial plant species, with a relative high species diversity and more alien species. To sum up, the distribution patterns of herb alien species in the Yiluo river basin was strongly influenced by both anthropogenic activities and physical environment.