Fatal interactions between Scots pine and Sphagnum mosses in bog ecosystems

In this study, we explore how Sphagnum mosses and Scots pine, Pinus sylvest ris, interact on different spatial and temporal scales in a boreal bog ecos ystem. We were particularly interested in relationships between the occurre nce of Sphagnum-dominated habitats and the occurrence of Scots pines of dif ferent age and size. Juvenile and adult pines occurred in different habitats. While juveniles ma inly occurred in Sphagnum-dominated habitats, predominantly with Sphagnum r ubellum, adult pines were found in habitats dominated by lichens, or with a sparse vegetation cover. Examination of surface peat cores sampled close t o adult pines revealed that almost all pines (97%) had established in a Sph agnum-dominated environment and that the habitat had changed since pine est ablishment. Scots pine is thus capable of changing and exterminating the Sp hagnum-dominated environment preferred for germination and establishment. P ines impede Sphagnum growth and peat accumulation significantly once they h ave reached a stem diameter of approximately 20 mm. It takes from 30 to 90 yr for a pine to reach that size. Our results show the importance of interactions between Scots pine and Spha gnum mosses in bog ecosystems. We conclude that interactions between trees and Sphagnum mosses are important driving forces behind the vegetation chan ge that has characterised boreal bogs during the Holocene.