Linking the biological traits of boreal bryophytes to forest habitat change after partial harvesting

Abstract

Biological traits are potentially important for understanding mechanisms of plant species responses to alteration of local habitat conditions through natural and anthropogenic disturbance. Forest harvesting is a prominent disturbance in the circumpolar boreal biome, influencing stand- and landscape-scale patterns of forest structure and biodiversity. We examined a range of variable retention harvesting intensities (10%, 50%, and 75% dispersed green-tree retention harvesting and unharvested controls) in terms of their effectiveness for maintaining mosses and liverworts with differing biological traits. Bryophytes were sampled in 20m radius plots 5–6years post-harvest in 24 forest stands (each 10ha) of two forest types (broadleaf-coniferous mixedwood, coniferous-dominated). We first examined the environmental factors that were the strongest predictors of species composition across the forest types and retention levels. We then used fourth-corner analysis to relate differences in the forest environment to species traits. Selected traits included bryophyte group, life form, habitat requirements, and reproductive and dispersal characteristics. The strongest predictors of species composition were ground-level moisture (estimated using growth of the moss Hylocomium splendens) and degree of canopy cover. Fourth-corner analysis showed that forest type, retention level, and their associated moisture conditions were closely related to the abundances of species characterized by different biological traits. Species with rare sporophyte production, larger spores, dioicous sexuality, or that require greater moisture or shade, were affiliated with higher retention and forest moisture. Reduced abundances of species with these traits after harvesting may detrimentally affect their capacity to disperse and re-establish, and suggests that moisture limitation is an important environmental filter that may restrict their representation at harvested sites. Coniferous-dominated forests supported higher abundances of several species types compared to mixed forests, including liverworts, acrocarpous mosses, and species that have greater moisture requirements, dioicous sexuality, or infrequent sporophyte production. This conveys the importance of coniferous forests as bryophyte habitat in mixedwood landscapes and the influence of canopy composition on regional species distributions. Understanding the tolerances of species exhibiting particular traits after harvesting may improve predictions about species extirpation risk and inform approaches to ensure their continued survival.