Deforestation in Thailand from 1976 to 1989 was mainly caused by roads and population growth. Building roads made it easier to convert forests into farmland, especially in areas with good soil. The increasing population needed more food, leading to more land being cleared for agriculture. However, other factors like soil quality and natural protections also influenced deforestation. Overall, roads and population pressures were the main reasons for the significant loss of forest cover in Thailand during this period.