Objective  Rural weeds refer to all wild weeds distributed in rural areas dominated by rural native herbs, which are an important part of rural biodiversity. However, the rapid development of rural urbanization and agricultural intensification has seriously threatened rural weed diversity and traditional rural habitats, but the scientific value of rural weed diversity still has not been attached with sufficient importance currently. Specifically, there are three research gaps at present. Firstly, existing researches on rural biodiversity mainly focus on the relationship between spatial patterns and biodiversity changes in urban and rural areas at the macroscopic scale, rarely considering the spatial and temporal evolution of rural biodiversity at the small and medium scales. Secondly, the traditional conservation and restoration of herbaceous communities and habitats are concentrated in urban and suburban areas, and there exist only limited quantitative researches on rural herbaceous communities. Besides, although it is uncommon to see the discussion of the characteristics of plant diversity and influencing factors thereof in a single or a specific habitat in previous researches, the integrity of rural ecosystems and the response mechanism of rural weeds to environmental influencing factors in rural habitats are seldom involved. To address the above-mentioned problems, this research proposes to identify the characteristics of rural weed diversity, explore the maintenance mechanism of rural weed diversity, and provide strategies for conservation of rural weed diversity, which are three crucial issues in rural biodiversity conservation.

Methods  This research selects a typical traditional village named "Canhuashan Village" in the hilly region of northeastern Sichuan as the research area, and conducts both qualitative and quantitative surveys to investigate the species and distribution of rural weeds in the research area. A total of four field surveys were conducted from October 2016 to August 2017 in the research area to record the characteristics of rural habitats and the distribution of rural weed species. The research selects several representative rural habitats for quantitative survey of native weed communities, with 48 fixed survey sample points being set up, and three 1 m×1 m quadrats being randomly demarcated in each survey sample point to record the species, abundance, height and coverage of native weeds therein. In addition, the research selects the Shannon-Wiener diversity index and the species evenness index to compare the diversity difference of native weeds in different habitats, and adopts the Jaccard similarity index to analyze the similarity in species composition of rural weeds. Finally, the research analyzes the species similarity among habitats by clustering, analyzes the main environmental factors influencing the distribution of rural weeds according to the ecological characteristics of different habitats and native weeds distributed therein by canonical correlation analysis, and then analyzes the maintenance mechanism of rural weed diversity.

Results  The research records a total of 263 species (188 genera, 65 families) of rural weeds in 21 different rural habitats, including 9 habitats around rural settlements (e.g., courtyards, roofs, wells and hedges), 9 habitats away from rural settlements (e.g., farmlands, ponds, ditches and field paths), and 3 marginal habitats (e.g., precipices, cliff forests and abandoned cultivated fields). The results show that the habitats with some specific moisture and light conditions, such as ponds and patch forests, have special species distribution patterns and relatively high species richness. Due to the long-term influence of both the natural environment and human activities on traditional rural ecosystems, various rural habitats with vernacular characteristics have been formed in different rural areas, providing suitable growth conditions for weeds. In addition, the results also show that illumination intensity and soil water content are the main environmental factors influencing the distribution and diversity of rural weeds. The existence of different rural production and life modes gives birth to and maintains diverse rural habitats, and presents different distribution patterns of ecological factors such as illumination and water. diversity, and special rural habitats maintain specific rural weed species. Furthermore, the research proposes the following strategies for the conservation of rural weed diversity based on the analysis of the maintenance mechanism of rural weed diversity: 1) Maintain a variety of rural habitats through the reasonable layout of rural "production-living-ecological" spaces; 2) restore and reconstruct the basic rural units of "hill-farmland-forest-pond-courtyard" for rural weed conservation; 3) protect rural small and micro habitats and build a three-dimensional habitat network in the rural area; 4) strengthen the application of rural weeds to restore natural vegetation; 5) inherit traditional rural ecological wisdom to promote effective conservation of rural weed diversity.