Forest understorey fulfils many important ecosystem services, such as mediation of carbon dynamics and habitat provision, and contains most of the plant diversity in boreal forest ecosystems. Changes in overstorey (tree) diversity may affect understorey diversity and species composition through changes in resource availability and soil conditions. Studies of understorey plant species composition in the Satakunta tree species diversity experiment have shown that tree species richness has significant effect on the understorey composition (but not species richness) with interplot compositional dissimilarity being significantly higher in monocultures than in mixtures.

Lingonberry (Vaccinium vitis-idaea)

Lingonberry (Vaccinium vitis-idaea)

Lingonberry (Vaccinium vitis-idaea) in flower

Lingonberry (Vaccinium vitis-idaea) in flower

Ferns 

Ferns 

Heather (Calluna vulgaris)

Heather (Calluna vulgaris)