On Dryopteris site type forests in Estonia

Fern-rich forest communities are presented in Estonia in mesic or moderately humid nutrient-rich habitats, in areas of drained mire forests, on floodplains and lower parts of talus slopes of the North-Estonian limestone escarpment (klint). In the recent official forest typology only one site type has been distinguished and labelled by the ferns: the Dryopteris site type in the scope of boreo-nemoral forests. The aims of the current study were (i) to clarify whether distinguishing between two fern-rich forest site types, one among the full-drained forests group and another in the boreo-nemoral forests group, is reasonable, and if so, then (ii) what the main characteristics of both considered forest site types are, (iii) what the main environmental factors determining the structure of these communities are, and (iv) what the mutual relationship between those forests and other fern-rich forest communities is. Our results asserted a distinct difference between the full-drained and undrained Dryopteris site type forests distinguished by the former scholars. The undrained boreo-nemoral fern-rich stands have developed in the same place in harmony with habitat conditions, while drained forests have significantly changed. It seems that despite some vagueness due to long-lasting post-drainage succession, it is nevertheless justified to recognise the fern-rich drained stands in Estonian forest typology as representing an autonomous forest site type in the group of full-drained forests. To avoid confusion in nomenclature, in the future, the undrained fern-rich boreo-nemoral forests site type could be named according to the most conspicuous indicator species as the Athyrium (filix-femina) site type and fern-rich stands on full-drained peat soils as the Dryopteris (expansa) site type.