Abstract: The seasonal and daily effects of deforestation on surface fluxes and the Bowen ratio in mid-latitudes and associated physical processes were explored by comparing forests and open lands based on the FLUXNET dataset. The results show that surface fluxes and the Bowen ratio decrease due to deforestation, with a noticeable decrease in sensible heat flux. A comparison of the effects of deforestation across different forest types indicates that changes in surface flux were more pronounced at noon on a daily scale. Mixed forests exhibited stronger surface flux changes than evergreen needleleaf forests but weaker than deciduous broadleaf forests. On a seasonal scale, sensible heat flux decreased in evergreen needleleaf and mixed forest sites, while latent heat flux decreased at evergreen needleleaf and deciduous broadleaf forest sites. A comparison of the effects of deforestation on surface fluxes across different climate zones revealed that for evergreen needleleaf forest sites, latent heat flux was mainly reduced in subarctic climates, while sensible heat flux was mainly reduced in marine west coast climates. For deciduous broadleaf forest sites, latent heat flux decreased mainly in marine west coast and Mediterranean climates; however, the sensible heat flux might increase in Mediterranean climates. Overall, the findings suggest that the physical properties of different forest types could influence the signs and magnitudes of seasonal changes in surface heat fluxes, and background climate could determine whether changes in sensible heat flux or latent heat flux were dominant. Our study provides observational evidence that can aid in the formulation and implementation of afforestation/reforestation policies in mid-latitudes. Furthermore, it offers valuable insights for model evaluation.