Early successional species improve soil nutrient contents, and affect establishment together with light and temperature. To detect differences in soil nutrients, temperature, and light between various forests types after the eruptions of Mount Usu, soil samples were collected, and temperature and light intensity were recorded by loggers in the forests. Sampling happened in mature and young forests including natural and planted forests during 2015–2017. To evaluate establishment success, the percentage similarity between the seedbank and standing vegetation was examined. Cluster analysis of the soil properties showed that most of the forests had similar chemical properties, but the plantation with Alnus ssp. formed its own group. Seedbank density was higher in the young forests than in the mature forests, with the Alnus ssp. containing plantation having the highest seedbank density (1430 seed/m²). Percentage similarity of the seedbank to standing vegetation decreased with successional age, and was largest in plantations. Temperature did not differ between the mature and old forests, but light intensity was higher in young forests and lower in plantations. Alnus spp. are nitrogen-fixers and improve the soil nutrients during early succession, but light and shading affected more the establishment success of seedbank than temperature and soil chemical composition.