Aesthetic of Suitable Tree and Shrub for the Green Space of the Mountainous Cities of Northern Iran

Introduction
Green space plays a very effective role in reducing the harmful effects of air pollution and noise pollution, strengthening cultural and social values, and reducing physical and psychological problems in the city. Urban vegetation is green spaces that are called the lungs of cities. Research shows that the use of native trees and shrubs is a priority in planting trees and shrubs, because native species are resistant and have the necessary beauty and pruning. They are also more suitable for making hedges than other non-native plants. Another advantage of using native species is their longer growing period. Along with all the environmental benefits that selected plants have for establishing urban green spaces, special attention should be paid to their ornamental and beauty issues. The aim of this research is to introduce ornamental trees and shrubs suitable for planting in the parks and green spaces of Deilaman city, with a preference for native species. It also aims to generalize it to cities with similar ecological needs and weather conditions. Hence, the answer to the question that according to the aesthetic characteristics, what are the tree and shrub species suitable for the green space of Deilaman city is considered.
 
Methodology
This research has a qualitative approach. In order to collect data, documentary sources and field studies have been used. The statistical population of the research was the collection of citizens living in the city of Deilaman (10,597 people). Using Cochran's formula, the number of people in the sample was equal to 371 people. In this regard, 30 questionnaires were used to check the reliability of the research tool in the pre-test stage. The Cronbach alpha coefficient for checking the reliability of the research tool was equal to 0.782, which confirms the validity of the designed questionnaire and questions. The range of studied green spaces was determined using Google Earth, and then the type of trees and shrubs in this area was identified. Also, the data of precipitation, minimum and maximum temperature, frost, and other elements were received from the meteorological station of Deilaman during the last ten years (2013 to 2023). In this regard, several species of trees and shrubs were selected according to the climate of the region and the time of blooming by studying reliable sources. The selected plants were approved by experts. Identification of native tree and shrub species was done by being in the area, making visual observations, and using the tree and shrub species identification guide. Finally, 30 native species of the region that could be used in urban green spaces were selected and approved by experts. The collected data were entered into SPSS software, and the results were presented based on graphs and tables.
 
Findings
According to the lowest and highest temperature recorded, -20 °C was considered as the temperature that the plants of Deilaman region have the ability to grow and tolerate. About 220 species of trees and shrubs were extracted from various sources and books, and then 107 species were selected according to their temperature tolerance, ornamental, and need for sunlight. Finally, 6 plants were separated from the rest in order to check the opinion of the respondents to plant them. The selected species for the green spaces along the streets of Deilaman city were also determined by the respondents' preferences as follows: Christmas pine (28.3%), maple (23.9%) and Kashmerian cypress (14.4%). Also, the species of maple and hornbeam with 11.7% and box tree with 10% are ranked the next. Furthermore, the selected species for the boulevards of Deilaman city were horizontal cypress (28.2%), elm (23.9%), and Kashmerian cypress (15.2%), respectively, and maple (12.9%), hornbeam (10.9%) and box tree (9.2%) were ranked lower. Moreover, the results obtained from people's answers showed that among the 6 selected species, Christmas pine (28.3%), Kashmerian cypress (22.2%), elm (16.1%), horizontal cypress (16.1%), alder (10.9%) and hornbeam (6.5%) were posed as first to sixth priorities for plant cultivation in city parks of Deilaman. Also, when people think about planting trees on the sides of roads, European nettle tree (26.5%), checker tree (24.8%), and yew (17.8%) are the most important trees. Three other tree species, hornbeam (14.4%), beech (10%), and oak (6.5%), are the next most important trees. Finally, the obtained results indicate that the first to third priorities for planting trees next to the schools of Deilaman city are Kashmerian cypress (30%), Christmas pine (20.4%) and ash (18.7%), respectively. Also, three other tree species, i.e., alder (15.2%), Caucasian wingnut (10%), and box tree (5.7%) were ranked fourth to sixth from the respondents' point of view. In addition to the above, a question with three options, “prefers,” “does not prefer,” and “doesn't matter,” was asked to evaluate people's preference for using native plants and planting them in green spaces and public possibilities. The results showed that 62.3% of citizens prefer to plant native plants of their region in public places, and 28.8% chose the option of no difference.
 
Discussion and Conclusion
In this research, it was found that species with non-green colors are more attractive to respondents than green species in urban spaces. According to the investigations carried out on the reducing power of the species, it can be stated that oak, plantains, pine, acacia, hornbeam, and white poplar are superior to other trees. So, the higher the height of the tree, the bigger its leaves, and the higher the density of foliage causes more reduction of pollution. On the other hand, broadleaf trees are not very suitable because they fall in autumn, and it is better to use mixed coniferous and broadleaf forests. These findings are consistent with the findings of the present study regarding the use of large and broad-leaved trees on roads and street edges. In general, to design a suitable and sustainable urban green space, special attention should be paid to all the positive and negative aspects of choosing plant species, especially trees and shrubs. The results showed that, among all plant species, especially tree species and shrubs, Elm, maple, alder, hornbeam, ash, box tree, Caussian wingnut, European nettle tree, and checker tree. Oak, beech, horizontal cypress, Christmas pine, and Kashmerian cypress were suitable for planting in this region. Based on all the indicators considered. Especially aesthetics, adaptability to weather conditions, and being native. The future perspective should be directed towards the design of software programs to select appropriate plant species for each region based on desirable environmental effects or functional benefits.