Population status and ecology of Pseudanomodon attenuatus (Hedw.) Ignatov & Fedosov in England

ABSTRACT Introduction. Pseudanomodon attenuatus, previously known as Anomodon attenuatus Hedw., is very rare in Britain. In this study, its population status and ecology in England were investigated. Methods. Located along the River Eden, Cumbria, the three previously known sites for the species in England were surveyed, plus three potential sites along the river. Abundance was evaluated in terms of ‘individual-equivalents’, each defined as an occupied 1 m grid cell, when the moss was growing on rock, or an occupied tree, when it was epiphytic. Geographical coordinates of each individual-equivalent were recorded with a GPS unit. Habitat and community composition were recorded by relevés. Results and conclusions. The species was found at each previously known site and a new site. A total of 127 individual-equivalents were found, and the actual total along the 10.4 km of riverbank surveyed was estimated to be 140–200 individual-equivalents. Along the whole River Eden may be as many as 250–1000 individual-equivalents, because significant amounts of potential habitat remain unsurveyed. The population is confined to the middle to upper inundation zone of the riverbank. About half of individual-equivalents occur on trees and about half on calcareous sandstone. Most trees are Alnus glutinosa; others include Acer pseudoplatanus, Betula pendula, Corylus avellana, Fraxinus excelsior, Quercus robur and Ulmus glabra. Common associates are Anomodon viticulosus, Didymodon insulanus, Homalia trichomanoides and Thamnobryum alopecurum. Reasons for the extreme rarity of P. attenuatus in Britain are uncertain and deserve investigation, as does its confinement to a narrow riparian niche, which appears untypical of P. attenuatus across most of its world range.