The vegetation history of the Agi Dagi region in the Ida Massif (NW Turkey) was reconstructed on the basis of pollen analysis of a topogenic peat bog. The analysis provided evidence of human impact on the woodland environment in Byzantine times and the centuries that followed. The bog was probably formed as a result of extremely wet conditions due to excessive forest degradation. It appears that the initial chestnut-oak forest, after a period of intensive clearings, recovered at first artificially and then naturally. A sequence of events: deforestation-afforestation continues to the present day. Chestnut woodland displayed an optimal development between the 11th and 14th centuries due to human influence. However, due to negligence and destruction, the gradual destruction of the initial chestnut-oak forest at the mountain vegetation level resulted in the extension of black pine forests at this level, leading to acidification of the soil and disappearance of the ephemeral flora of the original leafy forest. Consequently, biological diversity declined and the forest ecosystem became more fragile. The chronology for the last 1250 years has been established on the basis of a 14 C dated pollen profile from the lowest peat layer.