Limiting climatic factors and habitats ofErica tetralixat the eastern edge of its distribution range

Abstract

We determined the limiting climatic factors, as well as the preferred habitats, of Erica tetralix L. at the eastern limit of its distribution range in the eastern Baltic region. It was found that E. tetralix in this region is a typical bog woodland plant preferring the wettest Sphagnum-rich sites. Northern Atlantic wet heath fragments, base-rich fens and species-rich Nardus grasslands were other habitats for the species. The species composition in E. tetralix habitats resembled that found in appropriate habitats within its main distribution range, although the habitats in the eastern Baltic region lack many Atlantic floristic elements characteristic of wet heath. A generalised linear model describing the climatic niche of E. tetralix in Latvia suggests that mild winters, which exhibit a combination of a shallow maximum depth of soil freezing and a large number of days when the air temperature exceeds 0°C, as well as abundant annual and winter precipitation, are the main factors allowing the presence of E. tetralix in Latvia. The climate parameters at the eastern limit of the species’ distribution range are consistent with those recorded as being suitable for E. tetralix elsewhere. Our results reveal a strong relationship between oceanity and the distribution of E. tetralix. The climatic niche model suggests more climatically suitable areas in the Coastal Lowland geobotanical region where the species could potentially be found, most likely in bog woodlands. The future prospects to restore open areas of northern Atlantic wet heath with E. tetralix in Latvia are poor due to the decline in traditional land-use; these areas have turned into bog woodlands or been converted into agricultural land.