Application of three-dimensional greening in high-density urban space
(1) Commonly used three-dimensional greening forms
To improve the urban ecological environment, various new forms and new technologies of three-dimensional greening have been widely recognized and applied.(Lin, and Yu, 2020).(Table 3), It has become an important way to improve the high-density urban space environment.
Typical design mode of high-density urban three-dimensional greening
According to relevant information, statistics are made on the famous three-dimensional greening projects that have been built in some high-density cities. Among them, cities with more three-dimensional greening projects in high-density cities include Singapore, Hong Kong, Macau and other places in China.(Zhezhen, 2016).(Table 4).
According to the relevant data and statistical tables, the characteristics of the three-dimensional greening arrangement commonly used in high-density cities can be obtained:
Full-coverage green roofs are rarely used on the roofs of super high-rise buildings, especially dense green roofs(Besir and Cuce, 2018)., Sometimes solar photovoltaic panels are used instead of green roofs on the top roofs of super high-rise buildings to improve solar energy utilization.
There are many ways of vertical greening on the wall, including direct climbing, direct green wall, indirect green wall, etc.(Coma, Perez, de Gracia, Bures, Urrestarazu and Cabeza, 2017). Among them, the modular vertical green walls are generally used in low-rise buildings, while the plants in high-rise buildings are mainly climbing plants with strong wind resistance.
Technical application of three-dimensional greening
Technical points of vertical wall greening
(1) Application of modular three-dimensional greening in wall facade
Modularity generally consists of single modules, structural systems and irrigation systems(Peiqiang, Mei and Jiayi, 2017). It is fixed on a wooden frame or a stainless steel frame by lap joints. Specifically, it can be cultivated in the early stage according to the plant species and plant form in the module, and maintained for several months after installation. It has a long life and is suitable for large-scale difficult wall greening. In the modular medium, except for the planting holes of the medium, the rest of the medium is wrapped by the base tape, which will not cause soil erosion(Fig. 3)(Xue, 2019).
(2) Application of paving type three-dimensional greening in wall facade
It is a planting system that attaches the watering system and the wall planting bag to the waterproof membrane to form a wall, and can stabilize the planting system on the wall.(Guodong, 2015). The fixed place should use a unique waterproof fastening method, which is mainly composed of non-woven fabric, waterproof layer and automatic irrigation system(Fig. 4)(Qin, Henglin and Ye, 2016).
(3) Application of flower-style three-dimensional greening in building facades
The wall uses various building materials as the supporting structure, and then the flower pots with plants are fixed on the supporting structure to achieve a three-dimensional greening form of a flower arrangement. The advantages of this technology are that it is easy to install, disassemble and quickly build, and can quickly replace plants. It is often irrigated in the form of drip irrigation, and the plants selected for the flower arrangement are mainly flowers, which are mostly used for outdoor temporary construction of festival celebrations or gathering places, and the landscape viewing effect can be achieved in a short time(Fig. 5)(Huang, Lu, Wong and Poh, 2019).
(4) Application of planting through three-dimensional greening in building facades
The planting trough system usually includes a wall, steel frame, drip irrigation system, plant flower trough, etc. The wall is laid with a steel frame, an automatic drip irrigation system is arranged, and plants are finally discharged. The two methods that are used more now are the combination of horizontal strips or small planting troughs. Relatively speaking, the latter has stronger expressive ability and can be combined at will to form a variety of landscape effects. It can also be combined with the sun's movement trajectory and sunlight to meet the sunlight needs of plants(Fig. 6)(Xue, 2019).
Key points of roof greening technology
Load: Green roofs are widely used in countries with flat roofs and high-rise buildings. The weight of the planting substrate and plants will affect the load-bearing capacity of the roof structure(Cristiano, Deidda and Viola, 2021). There are higher requirements for the load capacity of the building structure. According to the "Technical Regulations for Planting Roof Engineering" (JGJ155-2013), the load of simple planting roof should not be less than 1.0kN/m2, and the load of garden-type planting roof should not be less than 3.0kN/m2(Huasheng, 2013). The plant load should include the initial plant load and the variable load that increases during the plant growth period. The initial plant load should meet the requirements in Table 5(Huasheng, 2013).
Key Plant Configuration Modes
There are many forms of three-dimensional greening. In the selection of plant materials, the ecological adaptability and garden artistry of plants should be considered first, and local characteristics should be formed by using local plant resources.
(1) The traditional climbing greening form is mainly used in wall greening. It has strong adaptability and rapid growth. Among them, Brocade and Parthenocissus quinquefolia are especially suitable for shady growth plants. Commonly used plants are Hedera Helix, Campsis, Lablab purpureus,Ipomoea nil, etc(Table 6)(Meiping, 2009).
(2) Modular greening uses artificial light soil when filling the planting matrix, and the thickness of the matrix selected according to the type of plants is also different. For example, the thickness of herbs needs to be 20-30cm(Suqin, 2019). Plant varieties need to choose cold-resistant, drought-resistant, shallow-rooted plants, and can choose types such as ground cover, perennial flowers, moss, and succulent. Because the planting container of the greening module is small, the plants generally choose the herb species with small volume and simple management and maintenance(Qin Jun and Yonghong, 2018).Plants such as Sedum lineare, Sedum sarmentosum, Sedum aizoon, etc(Table 7) (Qin, Henglin and Ye, 2016).
(3) The plants commonly used in the paving greening system are herbs with strong adaptability and easy maintenance and management. For example, it is easy to cultivate ferns such as Sedum lineare, Sedum sarmentosum, Ophiopogon japonicus, Asparagus cochinchinensis, Dichondra repens, Lolium perenne, Zoysia tenuifolia, or Nephrolepis biserrata so on(Qin, Henglin and Ye, 2016).The biggest advantage of the paved three-dimensional greening system is not only simple construction, good greening effect, but also easy maintenance and management. In addition to wall greening, it is also commonly used for urban slope greening (Table 8).
(4) The planting trough greening system is more common, and the variety of plants to choose from is more abundant, which needs to be replaced according to the season to ensure a good ornamental effect throughout the year.(Viecco, Jorquera, Sharma, Bustamante, Fernando and Vera, 2021). The optional plants are Hedera helix, Epipremnum aureum, Tradescantia zebrina, Ipomoea, Petunia, Jasminum mesnyi, Climbing Roses, etc(Table 9)(Qin, Henglin and Ye, 2016).
(5)Roof afforest more commonly used plants have Bidens alba, Tulbaghia violacea, Alopecurus aequalis, Arachis hypogaea, Momordica charantia, Butterfly bush and Kalanchoe blossfeldiana, etc(Table 10), Green roofs combined with agriculture to grow edible species(Hachoumi, Pucher, De Vito-Francesco, Prenner, Ertl, Langergraber, Fuerhacker and Allabashi, 2021)., which can reduce carbon footprint and increase the function of urban green infrastructure(Grullon-Penkova, Zimmerman and Gonzalez, 2020).