Arid Urban Green Areas Reimagined: Transforming Landscapes with Native Plants for a Sustainable Future in Aksu, Northwest China

Abstract

The exponential growth of the economy and society has resulted in a substantial need for superior urban green spaces, consequently fostering a significant surge in urban landscape construction. The integration of plant landscapes in urban landscape construction is crucial. The rational use of plant landscape resources to create high-quality urban green spaces is of great significance for promoting urban sustainable development. Hence, the primary aim of this study was to investigate the landscape and ecological functions of indigenous plants in the context of urban landscape implementation and then provide utilization strategies of indigenous plants for urban landscape construction. This research focuses on the utilization of native plants in Aksu’s urban green spaces (a city in northwest China). Through a contrastive analysis of the dust retention, windbreak and sand fixation, and landscaping capabilities of these native plants, certain indigenous species are identified as suitable candidates. Specifically, Styphnolobium japonicum and Ulmus densa exhibit a dust adhering per plant of 656.50 and 388.46 g·m⁻², respectively. Consequently, augmenting their planting proportion can effectively augment the overall dust adhering within the garden. The windbreak distances of Populus bolleana, Populus euphratica, and Styphnolobium japonicum were found to exceed 60 m, indicating their effectiveness in mitigating wind and sand erosion. Therefore, strategically planting these species can contribute to the establishment of a robust urban windbreak forest. Additionally, optimizing the arrangement of Rosa multiflora, Hippophae rhamnoides, Berberis thunbergii, and Salix matsudana can enhance the aesthetic appeal of urban gardens. The utilization of native plants holds promise in enhancing the ecological and landscape functions of urban gardens in Aksu. The effective enhancement of the ecological function and the landscape effect of urban gardens can be achieved through the appropriate reconstruction with native plants. The findings of this study hold significant reference value for the urban landscape architecture in arid urban areas.

1. Introduction

The harmonious coexistence between humans and nature poses a significant challenge on a global scale. Among the ecosystems most profoundly impacted by human intervention, cities stand out, and green spaces, as integral elements of urban ecosystems, offer a multitude of ecological services. Urban ecosystems provided by the urban environment include pollination and a fruit supply for humans and fauna [1]. These ecological services not only enhance the urban ecological environment and improve the quality of life for individuals but also serve as a reflection of the city’s humanistic environment and cultural heritage [2,3,4]. The process of plant landscape reconstruction entails making suitable modifications and alterations to plant species, spatial arrangements, and community compositions in response to the requirements of urban dwellers and the advancement of urban green spaces. It involves the deliberate preservation and redevelopment of plant landscapes to augment their quality [5]. Plants are an important part of garden landscapes. The scientific and reasonable use of indigenous plants can improve the urban ecological environment, enhance the characteristics of urban garden landscapes, and elevate the standard of plant landscapes [6].

Native plants offer numerous benefits in the realm of urban landscaping. Primarily, their abundance and affordability render them easily obtainable and transportable for use in urban landscaping following minimal processing [7,8]. Additionally, due to their extensive growth and evolutionary history, native plants exhibit robust adaptability to local growing conditions, soil compositions, and other pertinent factors [9,10]. Consequently, they are more likely to flourish in comparison to non-indigenous plants, thereby augmenting the distinctive attributes of urban garden landscapes [4]. Moreover, the maintenance and administration of indigenous flora during subsequent phases pose fewer difficulties, thereby mitigating financial burdens [11].

Nevertheless, in numerous contemporary urban landscaping endeavors, native plants are frequently disregarded. Though native species are acknowledged for their role in providing ecological services in urban landscapes [1], many cities tend to exotic species. This phenomenon results in a homogenous urban landscape and diminishes biodiversity [12], thereby directly affecting the landscape attributes and ecological resilience of urban green spaces and causing significant detrimental effects on urban ecosystems [13]. Therefore, it is crucial to understand the role of native species in urban landscapes. Furthermore, to improve the landscape attributes and biodiversity of urban gardens, the incorporation of native plants with ecological functionality and economic viability has emerged as a significant hurdle in contemporary urban landscaping endeavors. Consequently, there is an urgent need for comprehensive research on the utilization of native plants in the reconstruction of urban gardens.

The climate conditions in Aksu dictate that numerous indigenous plants possess distinctive attributes, including ornamental features, exceptional drought tolerance, and specialized functionalities. These unique attributes hold significant value in the creation of landscape plantings. By integrating these characteristic plants into landscaping projects, it becomes feasible to optimize the structure of urban plant communities, enhance urban biodiversity and stability, and elevate the overall aesthetics of urban gardens [14]. The promotion of native plants in urban landscaping in Aksu has the potential to generate positive ecological landscape outcomes [15] and yield significant landscape, ecological, and economic advantages. However, the available native plant species for the landscaping industry are limited, and the nursery market lacks supplies of native plants, with a limited variety of seedlings [16]. Additionally, some native plants have low ornamental value, which fails to meet market demand and restricts landscaping practitioners in their selection of native plants [16,17]. Furthermore, landscaping practitioners tend to rely on existing plant-pairing patterns, lacking an exploration of new native plants, which results in a lack of motivation in the nursery market to develop new native plants [16,17]. Therefore, the limited research on the landscape attributes of relevant native plants and the absence of cultivation techniques for native plant seedlings have resulted in a low utilization rate of native plants in Aksu’s urban landscaping [18]. Moreover, the presence of exotic plants poses a significant challenge to the ecological equilibrium and stability of urban garden landscapes, as they compete fiercely for limited space and nutrients [16]. Consequently, in order to bolster the sustainability of Aksu’s urban green spaces, it becomes imperative to undertake pertinent research on indigenous flora within the region.

Native plants in urban green spaces have multiple important ecological functions. They provide suitable habitats and food sources for animals, promoting diversity in urban ecosystems [19]; they effectively manage water resources in urban drought environments, reducing soil erosion and even purifying water quality to a certain extent [20]; harmful substances in the air adhere to them, thereby improving urban air quality [20]; and the diversity and attractive appearance of native plants add ecological landscape value to urban green spaces, enhancing the quality of life for urban residents [21]. These functions are crucial for the stability and sustainable development of urban ecosystems. Therefore, native plants applied to urban public spaces have certain potential in terms of landscape and ecological functions. By increasing the presence of native plants in urban green spaces, their important ecological functions in urban ecosystems can be effectively utilized, making a positive contribution to the sustainable development and ecological construction of cities. This study’s purpose is to explore the potential landscape and ecological functions of indigenous plants in urban landscapes by analyzing their current utilization in the green spaces of Aksu city and to provide suitable strategies of urban landscape construction for a sustainable future. The goal of the research is to provide guidance for the selection and implementation of native plants in landscape development in arid urban areas by evaluating the landscape and functional attributes of these plants. By increasing the presence of native plants in urban green spaces, the ecological advantages of urban garden construction can be enhanced.

2. Materials and Methods

2.1. Study Area

Aksu is situated in the northwestern region of China, in the central and southern areas of Xinjiang. It is positioned at the southern foot of the Tianshan Mountains and on the northern periphery of the Tarim Basin, ranging from 78°02′–84°05′ E to 39°31′–42°41′ N (Figure 1). The locality exhibits a typical continental climate, which is characterized by arid air, ample sunlight, significant fluctuations in daily temperatures, and distinct seasonal variations. The diurnal temperature difference usually ranges from 20 to 25 °C. Spring is marked by rapid yet unstable warming, and autumn is brief and experiences swift cooling. The annual mean temperature is 10.10 °C, accompanied by an average of 2747.7 h of sunshine annually and a frost-free period lasting approximately 185 days. The annual average precipitation varies between 43.9 and 65.3 mm, predominantly occurring during the summer months, constituting 59–67% of the total yearly precipitation. Conversely, winter experiences the least amount of precipitation, comprising only 2–4% of the overall annual precipitation, primarily in the form of snowfall. The annual potential evaporation ranges from 1950 to 2600 mm. The average annual wind speed ranges from 1.7 to 2.4 m/s, with heightened velocities observed during the spring and summer seasons. The maximum wind speed typically reaches approximately 20 m/s, predominantly from the northwest or west [22,23].

2.2. Plant Species Survey

To determine the usage of native and exotic plants in urban landscaping in the Aksu region, this study employed a survey approach to investigate the green plant population within 10 parks and 12 roadside green spaces in the aforementioned area. The survey methodology entailed 5 m × 25 m quadrats. A total of 22 sample points of urban greening were surveyed (Figure 1). Each sample point was meticulously examined to discern the species of the planted green plants, and pertinent data such as quantity, height, and crown width were meticulously recorded for each species. During the survey, five specimens of each type of green plant were selected. For each plant, we used a tree height meter to measure the actual height of the plant and a meter ruler to measure the lengths of the tree crown.

The distribution of native plants in the Aksu region predominantly occurs along ri- verbanks, surrounding farmland, and within desert areas. To ascertain native plant reso- urces appropriate for urban landscaping reconstruction in Aksu, this study undertook a survey of native plant species, with particular emphasis on woody plants. A total of 23 sample points of native plants were surveyed (Figure 1). The plant survey employed 25 m × 25 m quadrats, wherein the quantity of plants, height in meters, and crown width in meters within each quadrat were documented. The measurement method is consistent with that of urban greening in the Aksu region.

2.3. Data Processing and Analysis

To commence the floristic analysis of the prevalent plants in the surveyed region of Aksu, we referred to journal articles [4,22,23,24], “Flora of China” and “Flora of Xinjiang”, to inquire about the species names, families, genera, geographical origins, and ornamental characteristics of these plants. Subsequently, these plants were categorized into two groups: native plants and exotic plants.

In order to comprehensively assess the contributions of native and exotic plants in the Aksu region in terms of landscape and ecology, we conducted a series of comprehensive evaluations, including the collection and collation of survey data and related literature. These parameters cover the species number and individual number, frequency, species ratio, flowering period, ornamental value, plant height, crown width, spacing, leaf surface characteristics, and dust adherence amount per leaf area of native and exotic plants in the Aksu region. Using comparative analysis, we analyzed the differences between native plants and exotic plants in terms of dust retention, windbreak and sand fixation, and landscape functions. For data processing and statistical analysis, we used Excel 2017 and Origin 2019 software.

In order to accurately reflect the application of native and exotic plants in Aksu’s urban green spaces, the following formulas were calculated:

$$p_i=\frac{{\mathrm{N}}_{\mathrm{i}}}{{\mathrm{N}}_{\mathrm{T}}}\times 100\%$$

(1)

where $p_i$ is the proportion of the species of i, N_i is the number of the native species of i in the quadrat, and N_t is the total number of plants in the quadrat, ${\mathrm{N}}_{\mathrm{T}}={\displaystyle \sum _{\mathrm{i}=1}^{\mathrm{n}}{\mathrm{N}}_{\mathrm{i}}}$.

$${\mathrm{C}}_{\mathrm{i}}=\raisebox{1ex}{${\mathrm{S}}_{\mathrm{i}}$}\!\left/ \!\raisebox{-1ex}{${\mathrm{S}}_{\mathrm{T}}$}\right.$$

(2)

where C_i is the canopy density of the quadrat of i, S_i is the vertical projection area of the canopy, and S_T is the total area of the plot.

W = LAI × S_i × X

(3)

where W is a single plant’s dust-adhering capacity, LAI is the leaf area index, S_i represents the vertical projection area of the canopy, and X represents dust adhering per leaf area.

3. Results

3.1. Analysis of Native Plant Applications

3.1.1. Urban Landscaping Plants

Based on the findings from the survey conducted on landscaping plant plots, Aksu possesses a total of 66 species of landscaping plants distributed across 22 plots. There are 26 species of native plants in 15 families and 23 genera and 40 species of exotic plants in 22 families and 33 genera. The main landscaping plants used include Platanus acerifolia, Malus spectabilis, Salix matsudana, Populus bolleana, Prunus cerasifera, Buxus microphylla, and Ligustrum sinense, among others. Upon examination of the native and exotic plant varieties in the aforementioned plots (Figure 2), it becomes evident that exotic plants surpass native plants in terms of both prevalence and quantity. Concerning native plants, it was observed that merely two plots exhibited native plant species, with quantities of exotic plants surpassing 50%.

The frequency of occurrence of landscaping plants in the green spaces of Aksu is shown in

Table 1. High-frequency plants in the public green spaces of Aksu.

Plant Type	Species Name	Frequency of Occurrence
Exotic plant	Platanus acerifolia	17
	Ligustrum sinense	15
	Ulmus pumila’Jinye’	15
	Prunus cerasifera	14
	Fraxinus chinensis	12
	Malus spectabilis	13
Native plant	Salix matsudana	13
	Populus bolleana	7
	Styphnolobium japonicum	7

Note: The table only lists the high-frequency exotic and native plants in the public green spaces of Aksu.

. It was found that the most frequently occurring landscaping plants are Platanus acerifolia, Ligustrum sinense, and Ulmus pumila’Jinye’. In the Aksu garden green space, Platanus acerifolia, Malus spectabilis, Salix matsudana, and Populus bolleana have a higher species proportion, accounting for 10.23%, 4.43%, 14.27%, and 4.49%, respectively (Figure 3). Most of the native plant species have a lower species proportion compared to exotic plants. Among the exotic plants, Platanus acerifolia and Malus spectabilis have a higher species proportion, accounting for 10.23% and 4.43%, respectively. Therefore, it can be seen that in the green spaces of Aksu, native plants have a low frequency of occurrence, and their application is mainly achieved with Salix matsudana and Populus bolleana.

3.1.2. Native Plant Resources

Native plants play a crucial role in the local natural ecosystem, and Aksu boasts a wealth of native plant resources. There are 15 families, 24 genera, and 27 species of native woody plants, as well as five families, nine genera, and nine species of native herbaceous plants. The dominant families among these native plants are Rosaceae and Fabaceae, primarily found in proximity to farmland and riverbanks, with a lower diversity of plant species in desert regions. The existing native plants include Populus bolleana, Populus euphratica, Ulmus densa, Juglans regia, Salix matsudana, Hippophae rhamnoides, Tamarix chinensis, Lycium ruthenicum, Caragana sinica, Casuarina equisetifolia, and Neotrinia splendens, among others. Among them, Populus bolleana, Neotrinia splendens, Tamarix chinensis, and Casuarina equisetifolia have a higher species proportion, accounting for 16.65%, 9.65%, 5.67%, and 5.49%, respectively (Figure 4).

3.2. Functional Analysis of Native Plants

3.2.1. Dust Retention

It is common for the Aksu to have sand and dust weather, and garden plants have abilities to attract dust. Leaves are important sites to which atmospheric particles adhere. Several factors affect a plant’s ability to attract atmospheric particulate matter, including the LAI, dust-adhering capacity per unit leaf area, leaf size, surface roughness, and leaf surface characteristics, such as trichomes [22,23,24]. The dust adherence capacity per plant of nine common garden plants in the Aksu region was calculated using the formula in Section 2.3, as presented in

Table 2. Relationship between plant leaf morphology and dust adhering.

Plant Type	Latin Name	Leaf Characteristics	Crown Diameter (m)	LAI	Dust Adhering per Leaf Area (g·m−2)	Single-Plant Dust-Adhering Capacity (g·m−2)
Exotic plant	Platanus acerifolia	Large leaves with fuzz, leaf stalks with fuzz	5.70	9.66	9.15	985.09
	Prunus cerasifera	Hairless on both sides	2.68	11.17	4.27	251.96
	Fraxinus sogdiana	Smooth surface	3.34	6.93	4.06	242.85
Native plant	Styphnolobium japonicum	Surface with fuzz	4.77	9.19	6.75	656.50
	Ulmus densa	Smooth surface, fuzzy in vein axils on the back	3.57	9.71	6.21	388.46
	Salix matsudana	Long fuzz on leaf surface, short leaf stalk	2.75	10.45	3.29	248.10
	Populus bolleana	Smooth surface, fuzzy on the back	2.49	12.42	6.54	241.74
	Elaeagnus angustifolia	Hairless on both sides	2.30	9.46	4.62	157.07
	Morus alba	Large leaves, smooth surface, fuzzy on leaf surface	2.12	8.91	6.66	125.85

Note: Compiled based on literature sources [22,23,24] (Baidourela, A, 2015; Nurmamat, K, 2017; Tuerxun, M., 2016).

. These findings indicate significant variations in the dust-adhering capacities per plant among the garden plants in the Aksu region. Species with a high dust-adhering capacity (>400 g·m⁻²) include Platanus acerifolia and Styphnolobium japonicum, with dust-adhering capacities of 985.09 and 656.50 g·m⁻², respectively. Species with a moderate dust-adhering capacity (200–400 g·m⁻²) include Ulmus densa, Prunus cerasifera, Salix matsudana, Fraxinus sogdiana, and Populus bolleana. Species with a low dust-adhering capacity (<200 g·m⁻²) are Elaeagnus angustifolia and Morus alba. By comparing the dust-adhering functions of native and exotic plants, among the species with a high dust-adhering capacity (>400 g·m⁻²), Styphnolobium japonicum has trichomes on its leaf surface, to which more dust can adhere. It has a large dust-adhering capacity per unit leaf area, and its LAI is similar to that of Platanus acerifolia, making it a potential substitute for Platanus acerifolia in urban landscaping. Among the species with a moderate dust-adhering capacity (200–400 g·m⁻²), Ulmus densa has a large crown width and a high dust-adhering capacity per plant, surpassing some exotic plants. Salix matsudana and Populus bolleana have dust-adhering capacities per plant similar to those of exotic plants, but their dust-adhering capacities per unit leaf area and LAI are higher than those of exotic plants, making them suitable alternatives for exotic plants in urban landscaping.

3.2.2. Windbreak and Sand Fixation

Aksu experiences frequent windy days, and one of the main functions of garden plants is windbreak and sand fixation. The windbreak and sand fixation strength of plants is related to their height, coverage, and density. Plants with a greater height and density have better windbreak effects, and the greater the canopy closure, the better the sand fixation function. According to the survey results, the tree species in Aksu’s gar- dens with taller heights and longer windbreak distances are Populus bolleana, Populus eu- phratica, and Styphnolobium japonicum. Their heights all exceed 20 m, and the windbreak distance exceeds 60 m, as shown in

Table 3. Windproofing characteristics of garden plants.

Plant Type	Latin Name	Spacing (m)	Height (m)	Crown Diameter (m)	Canopy Density (%)	Windbreak Distance(m)
Exotic plant	Platanus acerifolia	3.5	15–20	3.35	26.26	45–100
	Robinia pseudoacacia	5	14–17	4.7	18.80	42–85
	Fraxinus chinensis	4.5	4–8	2.56	10.24	12–40
	Juniperus chinensis	3	4–5	1.32	13.52	12–25
	Malus spectabilis	5	3–5	0.5	2.00	9–25
Native plant	Populus bolleana	1.52	20–30	2.49	100	60–150
	Populus euphratica	3.2	20–25	3.42	26.81	60–125
	Styphnolobium japonicum	5	20–25	4.77	19.08	60–125
	Salix matsudana	3.47	8–10	3.89	30.50	24–50
	Morus alba	2.3	3–10	2.12	33.92	9–50

. Based on the planting spacing data of garden plants surveyed, the plants that have a higher planting density are Populus bolleana, Morus alba, and Juniperus chinensis. Considering the height, windbreak distance, and density of garden plants in Aksu, the tree species with strong windbreak and sand fixation functions are Populus bolleana, Populus euphratica, Platanus acerifolia, and Styphnolobium japonicum. Populus bolleana, Populus euphratica, and Styphnolobium japonicum are all native tree species, with Populus bolleana being the most widely used. It has a high planting density, small planting spacing, and high canopy closure, forming a dense crown in windbreak forests, resulting in a better windbreak effect. In addition, Salix matsudana and Morus alba among Aksu’s garden plants also have a high canopy closure and are native tree species. Therefore, selecting native tree species in the urban landscape can enhance its windbreak and sand fixation function and improve the ecological environment.

3.2.3. Landscape Functions

Urban garden plants must fulfill specific landscape functions, as they are crucial components in the creation of garden landscapes. Apart from their fundamental role as plants, they also contribute significantly to artistic expression within garden spaces. Furthermore, they enhance the environment and offer spaces for individuals to unwind, to appreciate nature, and to partake in cultural and recreational pursuits. Additionally, these plants can address spatial division requirements and adapt to seasonal changes within landscapes.

An analysis of the ornamental landscape functions of the plants surveyed is shown in Figure 5 and Figure 6. From the perspective of the existing exotic plants and native plants in terms of their landscape functions, the flowering periods of most plants, both native and exotic, are generally consistent. The majority of plants bloom in spring or summer, with fewer blooming in autumn. Spring and summer are the periods of the greatest landscape transformations in gardens, as the blooming, leafing, and fruiting of plants bring about significant changes in the landscape. The ornamental characteristics of native and exotic plants are consistent. Overall, native plants have similar landscape functions as exotic plants and can meet the needs of urban garden landscapes, as shown in

Table 4. Analysis of the ornamental characteristics of native plants.

Viewing Type	Latin Name
Flower-watching	Caragana sinica; Nitraria sibirica; Tamarix chinensis; Rosa multiflora; Apocynum venetum; Sphaerophysa salsula; Chondrilla piptocoma; Corethrodendron scoparium; Prunus armeniaca; Rosa xanthina; Rosa brunonii; Sophora alopecuroides; Limonium aureum; Lepidium latifolium; Peganum harmala
Leaf-watching	Berberis thunbergii; Populus euphratica; Morus alba
Fruit-watching	Elaeagnus angustifolia; Juglans regia; Malus pumila; Prunus armeniaca; Nitraria sibirica; Lycium ruthenicum; Hippophae rhamnoides; Calligonum mongolicum; Morus alba
Form-watching	Styphnolobium japonicum; Salix matsudana; Ulmus densa; Populus bolleana; Morus alba; Populus euphratica; Prunus armeniaca; Tamarix chinensis; Juglans regia; Malus pumila

. During spring and summer, one can enjoy the flowers of native plants such as Rosa multiflora, Nitraria sibirica, and Caragana sinica. The leaf color of native plants like Berberis thunbergii, Populus euphratica, and Morus alba changes in autumn, providing strong ornamental value. The summer and autumn seasons are the time when plant fruits ripen, with native plants like Hippophae rhamnoides, Elaeagnus angustifolia, and Lycium ruthenicum exhibiting outstanding ornamental characteristics. The landscape during winter and early spring is relatively barren, and the focus should be on observing the branches and forms of plants. For example, the branches of Tamarix chinensis turn red in winter, and Salix matsudana, Populus euphratica, and Styphnolobium japonicum have beautiful tree forms and attractive branches. This indirectly indicates that native plants have rich landscape functions and can partially replace exotic plants in gardens, making them suitable for urban garden landscapes.

4. Discussion

4.1. Application of Native Plants in Public Green Spaces

Presently, the utilization of indigenous flora in urban landscaping and green areas is constrained, indicating potential for enhancement. The surveyed green spaces in this study showed that only two plots exhibited native plant species, with quantities of exotic plants surpassing 50%. Compared to exotic plants, the use of native plants is relatively scarce both in terms of variety and quantity. In general, studies have shown a predominance of exotic plants in urban greening [25,26]. This is mainly because landscaping professionals tend to rely on existing plants in urban green space construction [17], resulting in a limited range of plant species. Additionally, exotic plants are easier to obtain than native plants due to both the resistance of these species to pests and diseases as well as the availability of seeds and seedlings that are easily acquired [1]. In urban greening of the Aksu region, the selected arbors are often tall [27], with large canopies and high ornamental value, such as Platanus acerifolia, which has the highest frequency and species proportion in Aksu’s green spaces. Moreover, with the increasing demand for aesthetics, some less visually appealing native plants, such as Casuarina equisetifolia and Haloxylon ammodendron, have been eliminated, whereas highly ornamental plants have been retained. This may be another reason for the low diversity of native plant species. Lastly, the limited availability of native plant seedlings in the Aksu region imposes certain constraints on the selection of plants for landscaping.

In landscape greening, the addition of native plants can not only effectively enhance the diversity of urban landscaping plants, but it can also ensure the stability of the overall urban ecosystem [28]. In the process of urban landscape reconstruction, a deliberate strategy can be employed to augment the presence of native plants, considering the specific circumstances of the Aksu region. Given the prevailing environment characterized by strong winds and frequent sandstorms in Aksu, it is advisable to augment the presence of indigenous plant species that possess dust adherence and windbreak capabilities.

Currently, in the urban landscaping of Aksu, there is a scarcity of native ornamental foliage plants, with only three species, Berberis thunbergii, Populus euphratica, and Morus alba, constituting 13.04% of the total. This discrepancy is noteworthy when compared to the abundance of flowering plants. Consequently, it is recommended to enhance the assortment and cultivation of native plants with ornamental foliage to attain a more harmonious and well-rounded plant composition within the urban environment as a whole.

4.2. The Potential to Substitute Exotic Plants with Native Plants in Urban Landscaping

4.2.1. Substitutability in Terms of Ecological Functions

Dust storms are frequent and disastrous weather events in Aksu [29]. The dust-adhering function of green plants in landscaping is crucial, but different tree species exhibit significant differences in their leaf dust-adhering capacity. Generally, factors such as leaf size, the presence of leaf trichomes, the shape of leaf veins, and the length of petioles directly affect the dust-adhering capability of leaves [30]. Native plants in Aksu have adapted to the harsh natural environment, resulting in leaves with strong dust-adhering abilities [31]. Tree species like the Styphnolobium japonicum and Ulmus densa have densely hairy leaves, which help with dust adhering to the leaf surface and preventing it from being easily blown away by the wind. Furthermore, leaf shapes that are shield-like or elliptical can also enhance the dust-adhering capacity [32], thereby increasing the amount of dust retained per plant. Compared with exotic plants, Styphnolobium japonicum and Ulmus densa have certain potential in dust retention and can replace exotic plants as urban garden greening species. Therefore, it is recommended to select native tree species with strong dust-adhering abilities, such as Styphnolobium japonicum and Ulmus densa, and increase their planting proportion in the transformation of Aksu’s urban landscape. This will help to reduce dust pollution and improve the quality of the living environment.

Aksu is severely affected by soil erosion caused by wind, so the reconstruction of the urban landscape should focus on selecting tall arbors with large canopies. By reducing the planting spacing and increasing the planting density, effective windbreak and sand control measures can be implemented [33]. The height and density of plants significantly influence the effectiveness of windbreaks. The windbreak distance in windbreak forests is generally three to five times the height of the trees [34]. Therefore, the taller the windbreak forest, the greater the windbreak distance. In Aksu’s urban greening, Populus euphratica, Populus bolleana, and Styphnolobium japonicum have more height and better windbreak distances compared to exotic plants. Furthermore, the windbreak effect is influenced by the dimensions of the tree canopy and the spacing between plantings. A larger canopy and narrower planting spacing contribute to a higher density of windbreak in the forest, leading to a more tightly closed canopy. This, in turn, creates a dense crown layer in the upper and middle sections. Consequently, when airflow traverses the windbreak, the dense crown layer in the middle exerts a more substantial influence on wind speed, whereas the top and lower layers have a comparatively lesser impact [35]. As a native plant, Populus bolleana has a smaller planting spacing than its canopy size, resulting in the highest density and canopy closure, and therefore, it has a stronger windbreak and sand control effect compared to exotic plants. Compared with exotic plants, Populus euphratica, Populus bolleana, and Styphnolobium japonicum, when used as windbreaks in urban garden landscapes, have significant potential in wind prevention and sand fixation. Therefore, in the reconstruction of Aksu’s urban landscape, it is recommended to select native tree species such as Populus euphratica, Populus bolleana, and Styphnolobium japonicum, which are tall and have a high planting density and a dense canopy, to replace exotic plants in urban landscaping. Furthermore, in order to effectively utilize windbreak and sand control measures, a mixture of plants with different characteristics should be chosen. This includes incorporating native shrub species, such as Hippophae rhamnoides, Elaeagnus angustifolia, and Tamarix chinensis, adjusting their planting proportions, increasing vegetation density, and comprehensively utilizing the ecological performance of various plants to enhance the effectiveness of the windbreak and sand control capacity.

Though native tree species have potential in urban garden landscapes, the ongoing urbanization process poses a serious threat to the resources of the native tree species in the Aksu region. The expansion of cities and construction activities, with a large amount of land being used for urban development, has led to a reduction in habitats for native tree species, significantly affecting their survival and reproduction [36]. Factors like environmental pollution and climate change have also led to a decline in the number and populations of some native tree species. This indicates the urgency of protecting the native tree species resources in the Aksu area. Some researchers believe that urban green spaces can serve as important relocation sites for the conservation of native plants, and that improvements in the urban environment, along with artificial cultivation techniques, can play a positive role in the protection and survival of native plants [1]. The United States, in its process of urbanization, realized early on the importance of native garden plant resources. In its urban planning, the country particularly emphasized the importance of greening and ecological protection. Many cities have dedicated green spaces and ecological reserves to ensure the effective protection and utilization of native plants [37]. Additionally, some European countries also focus on the protection of native garden plant resources in their urbanization process. In their urban planning, they pay attention not only to the aesthetic and functional aspects of buildings but also to ecological and cultural preservation. In many cities, ancient native plants coexist harmoniously with modern architecture [38]. Urbanization does not mean the complete abandonment of native plant resources. On the contrary, through scientific planning and management, we can meet the economic and social needs of urbanization while protecting and utilizing native plant resources.

4.2.2. Native Plants’ Potential in Terms of Landscaping

Plants, being the fundamental constituent of garden landscapes [39], manifest diverse colors and forms in response to phenological fluctuations, thereby engendering seasonal fluctuations in garden scenery. By skillfully arranging indigenous plants with varying flowering periods, a plethora of flower-viewing effects can be attained [40]. This investigation reveals that the flowering period patterns of both exotic and indigenous garden plants in Aksu exhibit remarkable similarities. Native plants exhibit similar functions as exotic plants in terms of the viewer’s ability to observe flowers, leaves, fruits, and forms. Compared with exotic plants, native plants have certain potential in landscape functions. Consequently, in the reconstruction of urban garden landscapes in Aksu, the substitution of exotic plants with native ones is a viable option that can potentially enhance the aesthetic appeal of the garden without compromising the overall landscape effect. It is imperative to identify and cultivate highly ornamental plants that are well suited for urban environments from existing natural vegetation [41]. This approach would contribute to the expansion and the availability of native plant seedlings within the landscaping industry.

In the context of garden reconstruction in Aksu, the configuration of plant community landscapes offers the opportunity to emulate natural plant communities and augment the stability of the community structure [42]. Plant communities transcend mere assemblages of individual plants, instead representing a systematic amalgamation. Consequently, when arranging plants, due consideration should be given to the variances in species with regards to spatial distribution, temporal patterns, and nutritional requirements [43,44]. In the context of urban development, it is imperative to employ a scientific approach in the selection of plant species, taking into account their ecological conditions, plant characteristics, and specific environmental requirements. This practice serves to augment urban plant diversity, foster equilibrium in urban ecological forms, and promote robust plant growth. Additionally, water resource allocation necessitates careful consideration. Given the prevailing water scarcity in the Aksu region, it is prudent to incorporate drought-tolerant plants during garden reconstruction, thereby mitigating water consumption and conserving water resources for urban greening purposes. In order to mitigate the potential decline in the visual attractiveness of urban garden landscapes caused by seasonal variations, it is imperative to consider the influence of seasonal factors on plants [45]. This can be achieved by incorporating a diverse selection of native plants with varying heights, flower colors, and leaf colors, while making use of their inherent hierarchy and color characteristics. By doing so, the artistic allure of native plant landscapes can be heightened, the hierarchical arrangement of plants can be enriched, and the scope of viable configurations for native plants can be broadened [46]. Furthermore, it is important to take into account the density and spatial configuration of the vegetation and establish multi-tiered plant community structures in order to optimize land resources and spatial utilization within urban areas. This approach guarantees that indigenous plants can efficiently exploit resources such as sunlight, soil fertility, and water throughout their growth stages, thereby yielding enhanced ecological advantages.

5. Conclusions

The utilization of native plants in urban garden landscapes within the Aksu region is relatively low. Appropriately increasing the proportion of native plants can contribute to the creation of high-quality urban green spaces in the Aksu region and realize the sustainable development of urban garden landscapes.

The utilization of indigenous plant species in urban garden greening initiatives in Aksu exhibits significant potential. Aksu is susceptible to sandy desertification, leading to the prevalent issue of dust weather. In the course of urban garden landscape reconstruction, the dust-adhering ability of native plants can be combined. For example, the use of Styphnolobium japonicum and Ulmus densa can augment the dust-adhering capabilities of garden greening.

The indigenous flora found in the Aksu region, namely, Populus euphratica, Populus bolleana, and Styphnolobium japonicum, exhibit commendable windbreak and sand fixation properties. These plants have the capacity to effectively impede wind movement at distances surpassing 60 m. By regulating their planting intervals, augmenting their population density, and enhancing their canopy coverage, a robust urban windbreak forest can be established, thereby mitigating the detrimental effects of wind erosion in the Aksu area.

The landscape functionalities of native plants align with those of exotic plants. Native plants, including Rosa multiflora, Hippophae rhamnoides, Berberis thunbergii, and Salix matsudana, possess commendable ornamental value, thereby augmenting the landscape impact of urban gardens. Employing native plants in the establishment of plant community landscapes enables the attainment of more resilient plant communities, consequently yielding heightened ecological advantages.

This study examines the ecological and landscape functions of indigenous plants, investigates their ecological and landscape function potential in the resto- ration of the Aksu landscape, and provides a certain reference value for the sustainable development of urban garden landscapes in arid regions. Nevertheless, certain limitations persist. Discrepancies in plant growth and interspecific competition may deviate from the conclusions drawn in this study, thus necessitating further investigation into the prospective application of indigenous plants in urban landscaping.