Abstract This study was conducted to investigate and analyze Euphorbiaceae plant resources in Sanling Mountain Forest Park in Zhanjiang City, Guangdong Province. A plant resource development and utilization value evaluation system was established by analytic hierarchy process (AHP) and used to comprehensively evaluate the development and utilization value of Euphorbiaceae plant resources in the area. The results showed that the comprehensive evaluation values of Sapium discolor, Sapium sebiferum, Flueggea virosa, Baccaurea ramiflora, Aleurites moluccana, Antidesma ghaesembilla, Phyllanthus emblica and Pedilanthus tithymaloides were greater than 2.65, performing well; the comprehensive evaluation values of Bridelia tomentosa, Glochidion puberum, Breynia fruticosa, Mallotus paniculatus, Mallotus repandus, Mallotus apelta and Alchornea trewioides were in the range of 1.962 2-2.596 4, performing ordinary; and the comprehensive evaluation values of Phyllanthus reticulatus, Ricinus communis, Croton crassifolius, and Sebastiania chamaelea were smaller than 1.96, which were relatively lower. S. discolor, S. sebiferum, F. virosa, B. ramiflora, A. moluccana, A. ghaesembilla, P. emblica and P. tithymaloides have great development value and can be developed and used in a planned and step-by-step manner, and Aporosa dioica and Euphorbia tirucalli with a lower comprehensive evaluation value but strong stress resistance and adaptability can be applied to the construction of ecological forests and shelter forests.
　　Key words Analytic hierarchy process; Euphorbiaceae; Garden application
　　Received: January 11, 2021  Accepted: March 6, 2021
　　Supported by Young Innovative Talents Project in Regular Institutions of Higher Learning in Guangdong Province (2016KQNCX231).
　　Gang SUN (1987-), male, P. R. China, lecturer, master, devoted to research about garden engineering and landscape ecology.
　　*Corresponding author. E-mail: [email protected].
　　Wild plants have the characteristics of good resistance, extensive management, and unique ornamental value. They can not only maintain ecological balance, but also can be used to enrich garden plant materials and beautify the urban landscape after development［1］. There are large areas of natural secondary forests in Sanling Mountain National Forest Park, Zhanjiang City, Guangdong Province, with diverse vegetation types and abundant wild plant resources, which are of great development and utilization value, and there is no investigation and research on wild plant resources in this area. Chinese scholars have successively studied and analyzed the history and current situation of wild plant utilization in China, and put forward the unsolved problems, suggestions and development prospects of garden application［2-5］. Ren et al.［6］ summarized the investigation status and characteristics of wild flower resources in China, analyzed several important application types of wild flowers in gardens at present, and put forward several suggestions for the protection and development of wild flower resources. Zhang［7］ used analytic hierarchy process (AHP), gray correlation method, and psychophysical method to analyze the evaluation results, and analyzed the results of wild plant communities based on the garden perspective, and put forward the problems to be solved in the research of wild ornamental plant resources. In this study, the most diverse wild plant resources of Euphorbiaceae in the area were selected for detailed field investigation, and a corresponding development and utilization value evaluation system was established by the analytic hierarchy process, and used to comprehensively evaluate the development and utilization value of wild ornamental plant resources in the area and screen out the Euphorbiaceae plants with good development prospects. This study provides a theoretical basis for the scientific development of vegetation in the park, and provides plant materials for the landscaping construction of Leizhou Peninsula and surrounding areas. 　　General situation of the research area
　　Sanling Mountain National Forest Park is located 3.5 km southwest of Xiashan City, Zhanjiang City, Guangdong Province, with a total area of 738.8 hm2. The park takes natural landscape resources as the main body and focuses on leisure, ecology, and popular science tourism. It is the "green pearl" and "ecological tourism new world" on the banks of the South China Sea, and is known as the "city lung" of Zhanjiang. The park is rich in plant species, including 354 genera of 120 families, which further include 318 species of trees, 536 species of shrubs, and 670 species of vegetation［8］. Among them, Euphorbiaceae has the most species, with 31 species of 23 genera, followed by Moraceae, Myrtaceae, Papilionaceae, and Gramineae in sequence.
　　Research Methods
　　Field investigation
　　This research started in October 2017 and used a one-year survey time to conduct a comprehensive survey of the park using a survey method combining route survey and systematic sampling. The survey content included statistical list of Euphorbiaceae plants, measurement records, and various indexes such as plant type, ornamental parts, flower and fruit color, flower diameter, leaf shape, leaf color, and ecological habits that are closely related to ornamental value, biological characteristics, and development and utilization potential. Photos and specimens were also collected.
　　Model construction and calculation
　　Evaluation index determination and model building
　　Comprehensively referring to literatures［9-11］ and expert opinions, a comprehensive evaluation model was built (Table 1). This study took the development and utilization value evaluation of wild ornamental plants of Euphorbiaceae as the target layer (A), and set the ornamental value, development and utilization potential, and biological characteristics as the upper layer indexes to form the criterion layer of the model (B). For the ornamental value, plant type, leaves, flowers, and fruits were set as the lower layer indexes. In terms of the development and utilization potential, the lower layer indexes were stress resistance, resource quantity, and development degree. The difficulty of reproduction, growth status, and ecological habits were set as the lower layer indexes of biological characteristics. Various lower layer indexes formed the index layer (C) in the model, and the wild plant species of Euphorbiaceae surveyed and recorded were the bottom layer (D) of the model. 　　Calculation methods and process
　　Hierarchical single arrangement and hierarchical total arrangement weight calculation: The relative importance weights of all factors at the same layer to the highest layer were called the hierarchical total arrangement. After calculating the weighted value of each evaluation index of the C layer relative to the B layer and integrating the weights of the B layer, the total arrangement weight of the C layer relative to the target layer A could be obtained. The weight coefficients were obtained through the evaluation of relevant experts and scholars, and the 1-9 ratio scaling method was adopted to construct the reciprocal judgment matrix for the hierarchical model. The YaahpV10.3 software was used to calculate the maximum eigenvalue of each reciprocal judgment matrix and its corresponding eigenvector W and CI value, and CR=CI/RI was used to calculate the CR value, so as to perform hierarchical single arrangement and consistency check and hierarchical total arrangement and consistency test (the total arrangement value of layer C to layer A was the combined weight coefficient BCDj of various influencing factora). The calculation results of CR, which measures the consistency of the judgment matrix in the evaluation model, were all less than 0.1, so the model judgment matrix passed the consistency check, and the weight values of different evaluation indexes were finally determined (Table 2, Table 3).
　　Evaluation index scoring and standards
　　After consulting references［12-15］ and professionals and conducting field investigations, 13 evaluation indexes closely related to ornamental value, biological characteristics, and development and utilization potential were selected and scoring standards (Table 4) were formulated. Based on the scoring standards, various Euphorbiaceae plants were scored.
　　C10 Distribution rangeWidely distributed in various regionsWidely distributed in multiple regionsWidely distributed medium number of regionsDistributed in few regionsDistributed in  individual specific regions within extremely narrow range
　　C11 Growth statusGrowing vigorouslyGrowing wellGrowing relatively wellGrowing ordinarilyGrowing poorly
　　C12 Difficulty of reproductionVery easy to propagateEasy to propagateHarder to propagateDifficult to propagateExtremely difficult to propagate
　　C13 Ecological habitHighly adaptable, regardless of the environmentStrong adaptability, low requirements for the environmentGeneral adaptability, with certain habitat requirementsPoor adaptability, with strict requirements for habitatsVery poor adaptability, with special requirements for habitats 　　Results and Analysis
　　According to the scoring standards in Table 4, each index of the wild plants of Euphorbiaceae was scored, and then the score value Vj and the combined weight coefficient BCDj of each influencing factor were substituted into the following formula:
　　A=∑ni=1BCDj·Vj.
　　The comprehensive evaluation value A was obtained, as shown in Table 5. The greater the evaluation value A, the greater the development and utilization value.
　　Analysis on the limiting factors of garden application
　　From the perspective of the total arrangement value of the constrained layer (layer B) to the target layer (layer A), the ornamental value has the largest weight value (0.668 7), followed by the development and utilization potential, and the he biological characteristics have the smallest weight value. It can be seen that ornamental value was the main consideration for garden application of Euphorbiaceae.
　　From the perspective of the total arrangement value of the index layer (layer C) to the target layer (layer A), the main limiting factor for the development and utilization of Euphorbiaceae plant resources was the size and peculiarity of flowers and fruits, followed by the quantity of resources, and the smallest limiting factor was ecological habits, indicating that flowers and fruits were not only the main objects for plant viewing, but also had a dominant position in the garden development and application of wild plants. In addition, the quantity of resources was also an important consideration factor, but this factor can be gradually changed through artificial breeding technology. Although the total arrangement value of ecological habits was the smallest, the ecological habits should also be considered in garden applications to create an adaptive ecological environment, so as to maximize the ornamental value of plants.
　　Comparison and analysis of comprehensive evaluation value A of Euphorbiaceae plants
　　The comprehensive evaluation values of B. javanica, A. bunius, A. wilkesiana, C. variegatum, E. cochinchinensis, E. milii, and E. pulcherrima were greater than 2.653 9, and they are also the plants with the highest degree of development and utilization. A. wilkesiana, C. variegatum, and E. cochinchinensis are rare colorful-leaf plants in South China, reflecting that colorful-leaf plants are preferred and there is still a lot of space for development. S. sebiferum and S. discolor are rare deciduous tree species in South China, which can be bred and cultivated as colorful tree species through introduction, domestication, screening and other procedures. 　　The comprehensive evaluation values of F. virosa, P. emblica, B. ramiflora, A. moluccana, A. ghaesembilla, and P. tithymaloides were in the range of 2.670-3.051 5. F. virosa with bright white fruit, P. emblica with a unique leaf shape and a beautiful tree shape, B. ramiflora, A. moluccana and A. ghaesembilla with plump tree shape and P. tithymaloides with peculiar appearance can be developed and utilized. A. dioica and E. tirucalli with comprehensive evaluation values of 2.276 3 and 2.487 5, respectively, can also be included in the key development tree species because of their good resistance and tolerance.
　　B. tomentosa, G. puberum, B. fruticosa, M. paniculatus, M. repandus, M. apelta, A. trewioides, P. cochinchinensis and M. philippensis showed average comprehensive evaluation value performance due to general ornamental value and fewer resources. They can serve as protective tree species for development after breakthroughs in scientific research or when the conditions are mature.
　　The comprehensive evaluation values of M. esculenta, R. communis, J. curcas, P. reticulatus, C. crassifolius, and S. chamaelea were lower, partly because of the average or poor ornamental value, and also because of their own limitations or the prejudice that economic tree species cannot be used in large quantities in landscaping. P. reticulatus, C. crassifolius, and S. chamaelea resources are relatively fewer, and can be used as Chinese medicinal materials through artificial breeding.
　　Conclusions and Discussion
　　Conclusions
　　According to the comparison and analysis of the comprehensive evaluation value A of each Euphorbiaceae plant in Table 5, the resource value summary and application recommendations of Euphorbiaceae plants in Sanling Mountain National Forest Park were made (Table 6).
　　Discussion and conclusions
　　Because people think that the garden application of wild plants is mainly in urban landscaping, they regard ornamental value as the main factor. However, garden application is not only about urban landscaping, but also includes the application of ecological forests and shelter forests. Tree species with low ornamental value but strong adaptability and resistance, such as A. dioica and E. tirucalli, should also be valued and developed reasonably. In addition, some economic tree species with high ornamental value, such as M. esculenta, can also be applied to landscaping construction.
　　The development of wild plants has problems such as unscientific and excessive pursuit of economic benefits. The development of wild plants is closely related to market demand. Some Euphorbiaceae species with high ornamental value and fast propagation have a high degree of development and application, while tree species with strong adaptability, strong resistance but poor ornamental value are rarely cultivated and bred in nurseries, which is not conducive to local ecological construction and protection. 　　Due to their own limitations, wild plants are currently not highly developed and utilized. For example, some plants of Euphorbiaceae have a certain degree of toxicity, which causes gardeners to hesitate to develop and use them. However, as long as they are applied properly, such defects can be avoided.
　　R. communis with a seed oil content of about 50% and J. curcas with a fruit oil content as high as 60% are very ideal industrial oil and green energy tree species. However, the current scientific research level is limited, which restricts the development and utilization of plant resources. Therefore, the development of scientific research is still an important measure for the development of plant resources.
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