The study is aimed to determine the C13 and O18 isotope ratios of plant species belonging to different life forms in different forest types in Yenice Forests hot spot. Carbon and oxygen isotope ratios are important in providing long-term information about plants. In our study, we grouped the plants by considering the life forms of Raunkiaer. We determined the C13 and O18 isotope ratios of life forms in different forest layers. We found highly positive correlations (p<0.05) between δ13C and δ18O isotope ratios in beech-fir and pure oak forest habitats. In the Yenice Forests, which have a megathermal climate type, plants in different forest layers have settled in the areas by choosing the life forms where water will be used most effectively. Geophyte (-27.38±2.27 p<0.05) is the life form with the highest C13 isotope ratio in terms of life forms. This situation proves that the group that felt the water deficiency the earliest is the geophyte form. For O18 isotope ratio, therophytes using surface water are the highest (24.06±3.92 p<0.05) life forms. It is important to examine the water deficiency in old forests such as Yenice Forests through life forms.