A major portion of Turkey's energy production is provided by lignite fired power plants. Most of these power plants lack a desulphurization unit, thus, giving rise to pollution of significant harm to the surrounding forests. One of these power plants operating since 1982, the Yatagan Thermal Power Plant, is located in the southwest of Turkey. Much research has already been done on the harm caused by this power plant to the Joinus brutia forests in its vicinity. Our studies aimed to focus on the forests surrounding the Yatagan Thermal Power Plant and to investigate the annual ring widths of various trees. Within the scope of this research, six separate sample sites had been taken into consideration between the years 1961 to 1982. The monthly mean precipitation was taken as an independent variable and annual ring widths as a dependent one to form a linear regression equation. With the aid of this regression equation the annual tree ring widths were calculated as they should have normally to be, when not influenced by the power plant operation. The results indicated that air pollution caused an annual average decrease in ring widths of about 0.7-2.8 mm.