Plant selection for semi-arid urban landscapes with an emphasis on climate change (case study: Tehran)

Introduction:
Urban landscape, especially urban forest and city trees, usually has vital and various effects on the mental and physical health of humans, environmental embellishment, and mitigating the destructive effect of climatic changes like wind storms and flood control, as well as reduction and control of hazardous contaminants. Choosing appropriate plants for urban landscapes is vital to avoid potential financial and environmental losses that may occur if all selection parameters are not taken into account. The determination of plant species assessment indices in urban green space in Tehran does not have any special standard. Therefore, the aim of this study was to make a sustainable green space for Tehran metropolis due to its arid and semi-arid climate, which poses more challenges to choose suitable plant species for green spaces.
Material and methods:
In our study, the methodology structured a hierarchy consisting of a goal and sub-ordinate attributes of the problem. Other important components of this methodology were a pairwise comparison between various parameters used to quantify value judgments, and the matrix multiplication used to convert level specifi c criteria into a larger decision priority. After grouping plants, selection parameters have been defined for each plant group. Plant species were comparatively graded for each parameter by a group of eight specialists. Analytical hierarchy process (AHP) technique and hierarchical cluster analysis have been utilized to find the most adaptable plant species for the area according to the main selection parameters of zone tolerance, urban conditions, esthetics, maintenance, growth characteristics, and specific features. A table was designed in questionnaire format and distributed between 8 respective experts for coefficient value determination and then the coefficient value was obtained by Expert choice software. The dominant plant list of Tehran and the world was prepared, and plants that exist at Tehran botanical garden and had acceptable results were chosen. Scoring the plant species was performed from 0 to 3 with the values of 0.5, 1.5, and 2.5 being used for the intermediate state. After multiply each factor weight and each species score, the final plant weight was obtained and the proper and relative proper plants weredetected. Because of the importance of climate change, the indices influenced by climate change were determinedby future weather prediction using Larse-wg-5.1 software under the Hadcim3 model that have three scenariosbetween 2011-2030 and 2045-2065. Weight of these indices was multiplied at species scores and then the properand relative proper plants were prioritized and introduced for planting.
Results and discussion:
Pointed tree species like Ceratonia silique, Gleditsia spp., Ziziphus jujube, Tamarixparviflora, Sophora japonica, Pistacia chinensis, Guercus coccinea, Quercus douglasi, Seltis sp., and Guercusagrifolia were determined as suitable choices for green space planting. Pointed shrub species like Cercis chinensis,Berberis thunbergii, Eleagnus pungens, Ribes sp., Spartium junceum, Punica granatum var.pleniflora, Rhusglabra, and Pyracantha coccinea were suitable as well.
Conclusion:
In general, the results showed that many dominant green space plants were not proper species andthere are more suitable plants that have received less attention. Before introducing new plants to the urban environment,they should be experimented on in a small scale for several years to confirm that they will not change theecology of the whole region through invasion or posing a threat to any local plant species.