Objective Faced with the constraints of fragile natural ecological conditions, urban development in the arid and semi-arid areas in northwest China requires the establishment of new ecological processes under artificial interventions. The interaction between the arid and semi-arid natural environment and the complex and variable artificial environment provides the possibility and necessity of diverse habitat conditions for urban built environment. Urban green space is the basis for providing suitable urban biodiversity. Based on the perspective of urban habitats and their vegetation characteristics, this research proposes a methodology and strategy that can guide the practice of ecological design of urban green space, aiming to provide theoretical support and technical guidance for the ecological construction of urban green space in the arid and semi-arid areas in northwest China.

Methods The heterogeneous characteristics of urban habitats are recognized at the medium and small scales, and their matching relationships with the design levels and contents of urban green space are sorted out, and then, from the perspective of urban green space design practice, the formation and maintenance mechanisms of urban habitats and their vegetation characteristics at the medium and small scales are transformed into the strategies for ecological design of urban green space.

Results First, based on the multi-scale and heterogeneous characteristics of urban habitats and the multi-dimensional attributes of urban plantscape, a framework for the ecological design of small and medium-scale urban green spaces is constructed. Second, based on the moisture conditions and vegetation characteristics, as well as the types and construction needs of urban green spaces, the ecological design types of urban green space in the arid and semi-arid areas in northwest China are divided into four categories: Ecological design type of urban river, lake and artificial wetland, ecological design type of urban woodland and grassland, ecological design type of road and square, and ecological design type of urban specific habitat; and three types of ecological design zones (conservation zone, restoration zone and construction zone) and their ecological design strategies are proposed. Based on the aforesaid four ecological design types, the three types of ecological design zones are refined into 18 specific ecological design zones that can be applied to arid and semi-arid areas in northwest China. Finally, the strategies for optimized design of site habitat diversity, design of plant community diversity and design of the science popularization display system are proposed. 1) In the optimal design of site habitat diversity, the “water” factor is taken as the core content of the optimal design of site habitat for urban green spaces in arid and semi-arid areas, and design strategies applicable to different types of ecological design of urban green spaces and their zoning are proposed in three aspects, namely vertical design, rainwater organization and water retention design, as well as soil treatment and irrigation design. 2) In the plant community diversity design, the basic principles for plant community design and the strategies for plant species selection and plant community design are proposed for restoration and camping areas of different ecological design types, and recommended planting types are proposed based on the natural vegetation types of major cities in arid and semi-arid areas in northwest China. 3) In the design of the science popularization display system, the knowledge content and spatial layout strategy of four types of science popularization display, namely comprehensive guide of ecological information, display of natural environment features and ecological environment protection, display of ecological practice, and warning of ecological protection, are proposed.

Conclusion Transforming the formation and maintenance mechanisms as well as vegetation characteristics of small and medium-scale urban habitats into the ecological design approaches for urban green space can provide theoretical support and technical guidance for ecological construction of urban green space in the arid and semi-arid areas in northwest China. Different types of ecological design and zoning of urban green space may serve as the basic unit for the construction of macro-scale habitat pattern, and as the basis for the design of micro-scale urban habitat diversity, which can become the bridge between macro-scale and micro-scale habitat creation. The design of plant community diversity can make full use of heterogeneous and diverse urban habitats to shape low-cost, high-efficiency, resilient and sustainable plantscape. The construction of multi-scale and heterogeneous urban habitats and their vegetation characteristics can link different landscape patterns to form a functionally continuous biodiversity pattern that can bring higher ecosystem service functions and social benefits as an important part of urban green infrastructure.