城市化对本土植物多样性的影响——以廊坊市为例

虽然城市化对生物多样性影响的研究在发达国家是一个重要的研究领域,但是在发展中国家这方面的研究不多。通过案例研究,分析本土植物多样性沿着城市化梯度的变化,及其与生境土壤因子的关系。在廊坊市,中国北部一个快速城市化的地区,沿着中心城区、城区、郊区、远郊区城市化梯度,每个梯度选取6个样地进行本土植物多样性调查,记录种类数、多样性和种类组成,并分析了多样性指数。与远郊区相比,中心城区失去了88%的物种,物种多样性下降了78%,城区物种多属于禾本科、藜科等耐践踏、耐土壤紧实度的物种。远郊区的本土植物属于45个科,科数大于城区物种。相似性指数表明,城区和郊区大部分物种相同,但是远郊区差异较大。DCCA分析表明,土壤总氮、有机质含量是影响物种城市化分布的主要因素。城市化促进了物种分布的匀质化。

Effects of urbanization on indigenous plant diversity: a case study of Langfang City, China

Although documenting the impact of urbanization on biodiversity has been an important research topic in many developed countries, research on this topic is rare in the developing countries. The aim of this study is to investigate the changes in indigenous plant diversity along an urbanization gradient and the relationship between indigenous plant species and the soil factors in their habitat. In Langfang City, a fast-urbanizing city in northern China, six sites with size of 20 m×20 m each were sampled along central urban, urban, suburban and rural gradient, respectively. In each site, 2 plots with size of 2 m×2 m each for shrub species and 3 plots with size of 1 m×1 m each for herbaceous species were selected for plant community survey. Species richness, diversity, and composition of indigenous plants were recorded and analyzed at each site. Our results suggested that urbanization processes have a significant effect on the number, diversity, proportion, and composition of indigenous plant species. A total of 11 species were recorded in the central urban, 14 species in urban, 46 species in suburban, and 95 species in rural areas. Species diversity reflected by the Shannon-Wiener index increased from central urban to rural areas, with relatively low standard deviations in central urban but relatively high standard deviations in rural area. Evenness increased from urban to rural areas, with high values in central urban spaces. The standard deviation of evenness values was relatively high for all sampling sites, with a significant difference according to the Pearson-test (average 0.91 at P=0.05) along the urbanization gradient. There were six families in central urban areas, ten families were recorded in urban areas (mainly Gramineae), 19 families in suburban spaces and 45 families in rural areas. In central urban and urban areas, most indigenous plants belonged to the Gramineae and Chenopodiaceae families, but in the suburban areas species compositions were mixed with members from Gramineae, Compositae, Leguminosae, Chenopodiaceae and Asclepiadaceae. In central urban areas, the main indigenous plant species were Eleusine indica, Digitaria sanguinalis, and Setaria viridis. The urban area communities were dominated by Digitaria sanguinalis, Eleusine indica, Chloris virgata, Setaria viridis and Chenopodium album. Amaranthus retroflexus is present in suburban areas. In rural areas, Amaranthus retroflexus becomes replaced by Kochia scoparia. The similarity index showed that most of the species distributed in the urban area were also found in the suburban, but not in the rural areas. With increase of distance to central urban, the Jaccard index decreased. Most indigenous plant species growing in rural or suburban areas were also likely to grow in central urban than in urban areas. The DCCA analysis showed that total soil nitrogen is the main factor influencing the spatial distribution of indigenous plant species under urbanization. Soil conductivity and total organic matter, and active potassium have a relatively lower effect, and soil pH has the lowest effect on the sample ordination in the DCCA. The plant species surviving in urban areas had high tolerance to tramping, soil compaction and mowing, most of them belong to the Gramineae and Chenopodiaceae families. Thus, urbanization has eliminated most local species and only most common species are left. This result suggests that, in general, urbanization facilitates the homogeneity of plant species distributions worldwide.