Effects of climatic parameters and air pollutants of Tehran city on the growth of Pinus eldarica in Chitgar forest park during time series (1975-2015)

Climate change and environmental pollutants affect the growth of plant species. These effects can be recognized in the tree growth rings. This study aimed to investigate the effects of the precipitation and temperature in four decades (1975-2015) and air pollutants in the last decade on the average growth of pine trees (Pinus eldarica).

The studied area is Chitgar Forest Park located in the northwest of Tehran city and the studied species is the forest pine (Pinus eldarica). The research method is descriptive, the required climatic information was obtained from Mehrabad meteorological station and sampling was done by disc cutting from 10 forest pine trees. After preparing the samples, the number and width of annual rings were counted and measured using binoculars and a measuring table. One-way analysis of variance (ANOVA) was used at a significance level of 5% to investigate the significant difference in growth width in four decades.

The results show that there is no significant difference between average precipitation in four decades, while average temperature and average growth have significant differences (p < 0.05). The amount of growth based on the growth index has decreased during four decades, and this decrease is more significant and obvious in the fourth decade due to the increase of pollutants such as ozone (O3) and nitrogen dioxide (NO2).

In general, the growth of forest pine trees has decreased during forty years with the increase of average annual temperature, which excessive decrease in the fourth decade is caused by pollutants such as ozone and nitrogen dioxide. It is suggested to do more research on sensitive species planted in urban areas to better understand the effect of pollutants on the growth and development of trees.