Temperature, precipitation and other environmental patterns change fast due to climate change. This rapid change might cause problems for tree species which can only shift their distribution range slowly. To see how the functional species composition of forests reacts to climate change across Japan, we analysed long-term monitoring data from forest plots across the country. We expected warm favouring plant functional types (PFTs) to shift northward into areas traditionally too cold for them, in other words detect an increase of evergreen broadleaf (EB) saplings in deciduous broadleaf (DC) forests, and an increase of DC saplings in boreal conifer (BC) forests. We measured changes using the difference in relative abundance between the first and final years of the surveys and correlated them with weather data, presence of animal disturbance, and the age of forest in the plot among others. We found that the majority of the forest plots examined did not change their dominant PFTs, but that EBs increased in their abundance regardless of age and other factors. DB trees also increased their abundance in BC and temperate conifer (TC) forests, while slightly decreased their presence in DB forests. However, this change resulted not only from increased warm-favouring sapling intrusion intro traditionally colder forest types, but also from increased mortality of mature trees in the original PFT groups. Saplings from all PFTs, apart from TC, increased their relative abundance, while the abundance of mature trees decreased in the BC and TC group, indicating that mature conifers are more sensitive to climate change than their broadleaved counterparts. Herbivory and insect damage had little impact on the results, while both monocultures and highly diverse forests showed little change in the relative abundance of PFTs, suggesting higher resilience to intrusions. In conclusion, we found that EB trees benefit most from the changing environmental conditions, while TC trees suffer most from it, followed by BC trees. The movement of the distribution range of saplings had less impact than previously expected though, with mortality of mature trees playing a larger role.