Environmental controls of raised-bog vegetation in the Baltic boreo-nemoral zone

Raised peat bogs harbor unique vegetation types in specific hydrological conditions. Environmental controls of peat bog vegetation are relatively well known for the boreal zone, while in the European boreo-nemoral zone healthy raised bogs are nowadays very rare. By contrast, Latvia, located in the transition zone between the nemoral and the boreal biomes, still has a large number of active raised bogs. The aim of the present study was to characterize the environmental controls on raised bog vegetation structure, species composition and ecology in Latvia. The study includes 17 raised bogs, where vascular plants, bryophytes and lichens were recorded in 480 sample plots and related to environmental variables (microtopography, litter cover, electric conductivity, pH, and macroelements Na, K, Ca, Mg and P in bog surface waters). The factor best explaining total species richness and composition was microtopography, which also affected most other explanatory factors. Thereby total species richness and cover were highest on hummocks. However, the importance and direction of the effects of microtopography and the other factors differed between vegetation groups. When disregarding microtopography, species composition was most strongly correlated with alkaline ions and litter cover and for bryophytes also with vascular plant cover. The present study is the first wide-scale study in Latvia relating raised bog vegetation to environmental conditions.