No abstract

Old-growth forests are often considered as biodiversity hotspots for bryophytes because of their diversity in environmental niches or microhabitats and forest continuity. Following this hypothesis, old-growth forests would be expected to house species and functional traits associated with species dispersal different from mature forests. In this study, we compared bryophytes in old-growth and younger forests in terms of species composition, functional trait values, and microhabitat associations. We studied bryophytes in 22 sites distributed across three age classes (18 to >200 years) in boreal forests (eastern Quebec). Richness of liverworts, vegetative-reproducing species, and species with infrequent sexual reproduction were higher in the oldest age class. Species richness was best explained by the availability of coarse woody material (CWM) and other microhabitats, and community structure was best explained by balsam fir basal area. Microhabitats most often associated with indicator species were organic matter, CWM, and pits. Our results indicate that communities associated with older forests are potentially sensitive to forest management as they differ in composition and functional traits from other age classes, with many species characterized by reduced dispersal capabilities and tolerance to competition. An approach that combines critical source habitat protection for dispersal-limited species with protection of critical microhabitats in neighboring managed stands are necessary to allow successful recolonization and maintain bryophyte diversity in managed landscapes.

Old-growth forests play a decisive role in preserving biodiversity and ecological functions. In an environment frequently disturbed by fire, the importance of old-growth forests as both a carbon stock as well as a source of emissions when burnt is not fully understood. Here, we report on carbon accumulation with time since the last fire (TSF) in the dominant forest types of the Clay Belt region in eastern North America. To do so, we performed a fuel inventory (tree biomass, herbs and shrubs, dead woody debris, and duff loads) along four chronosequences. Carbon emissions by fire through successional stages were simulated using the Canadian Fire Effects Model. Our results show that fuel accumulates with TSF, especially in coniferous forests. Potential carbon emissions were on average 11.9 t·ha −1 and 29.5 t·ha −1 for old-growth and young forests, respectively. In conclusion, maintaining old-growth forests in the Clay Belt landscape not only ensures a sustainable management of the boreal forest, but it also optimizes the carbon storage.