Bryophyte and lichen communities in mature to old-growth stands in eastern boreal forests of Canada

Abstract

We sampled 22 black spruce (Picea mariana) - feathermoss (Pleurozium schreberi) sites (80 to >200 years) to describe and assess the diversity of bryophyte and lichen communities as a function of time since fire and site characteristics. Old growth had no more species than younger forests. We think that this result might be explained by the phenomenon of paludification, which is a major process in this region. Axis 1 of a nonmetric multidimensional scaling ordination (NMS) of terricolous species was interpreted as a paludification gradient. Mature forests were characterized by Pleurozium schreberi, Ptilium crista-castrensis, Polytrichum commune, and Dicranum polysetum, and older sites by a greater abundance of Sphagnum. Axis 1 of epiphytic species ordination (NMS) was interpreted as a gradient of time since the last fire. Abundance of Tuckermannopsis americana, Hypogymnia physodes, and Bryoria furcellata was greater in mature forests. In contrast, Mycoblastus sanguinarius, Bryoria trichodes, and Usnea spp. were more abundant in older forests. The abundance of epiphytic lichens increased with tree age, whereas their richness was higher in sites where trembling aspen (Populus tremuloides) and jack pine (Pinus banksiana) were present. Since species composition varied with time since the last fire, it is important to preserve the diversity of successional stages at the landscape level and the structural diversity at the stand level to maintain the bryophyte and lichen communities.