Bryophyte and polypore richness and indicators in relation to type, age and decay stage of coarse woody debris of Picea abies

Abstract

Coarse woody debris (CWD), which is in low supply in intensively managed forest, is an essential habitat for many species of bryophytes, fungi and insects. We investigated richness of bryophyte and polypore species on CWD of Norway spruce Picea abies (L.) Karst. in relation to CWD type, size, decay stage and age since mortality. We also identified indicator species for the bryophyte and polypore communities on dead trees in various decay stages. CWD age since mortality was determined to assess the time period of potential colonization by the indicator species. The study was conducted in Latvia, located in the hemi-boreal forest zone, where such information was generally lacking. The larger part of spruce CWD was in early decay stages, due to the legacy of forest management and recent disturbance events. The maximum age of spruce CWD was 48 years, and age of the majority of CWD pieces in advanced decay stages was 20 to 40 years. The estimated ages of CWD suggest a more rapid decay rate in the mesotrophic habitat studied in the Eastern Baltic region than reported previously for northern Scandinavia and mountainous regions. Bryophyte species richness was significantly affected by CWD diameter, type (higher on snapped logs) and decay stage (lowest in initial decay stage). Polypore species richness was significantly lower on snags, and higher on logs in early decay stages. A succession of epixlyic species was shown from common polypore species Fomitopsis pinicola and Trichaptum abietinum at start of wood decay to indicator bryophytes like Nowellia curvifolia in early decay stages after loss of bark, Lepidozia reptans and Jamesoniella autumnalis in mid stages and Herzogiella seligeri with epigeous species in late decay stages.