Lichen chronosequences (postfire and postharvest) in lodgepole pine (Pinus contorta) forests of northern interior British Columbia

Abstract

Lichen community development was examined in a postfire chronosequence from lodgepole pine (Pinus contorta Dougl. ex Loud var. latifolia Engelm.) forests in the Omineca region of north-central British Columbia and in stands originating from logging in the early 1980s. Fire-origin stands showed dense regeneration of pine and widespread growth of acrocarpous mosses such as Polytrichum spp. As canopy thinning progressed, Cladonia spp. lichens initiated development at the forest floor surface. By 50–100 years after stand origin, Cladina mitis and Cladina rangiferina dominated at the forest floor surface, remaining at high cover values well into the second century of stand development. Late seral stages of stand development (approximately 150+ years) showed increasing basal area and canopy cover of lodgepole pine, with feathermoss mats (e.g., Pleurozium schreberi) replacing terrestrial lichens at the forest floor surface. Stand ordinations confirmed these groupings of species. Stand structural factors that correlate best with lichen mat development include tree density, basal area, and canopy cover. Changes in the leaf area index and associated litterfall loading appear to precipitate the replacement of terrestrial lichen mats in "old-growth" stands. Interestingly, this trend was reversed in mature stands where winter harvesting of trees removed canopy cover without disturbing the forest floor surface. Lichen cover in these sites, 15 years after harvest, exceeded that of comparably aged fire-origin stands. Summer harvesting (with a presumed greater disturbance of soils) did not trigger a similar rebound of lichen communities. Instead, vascular plants appeared to invade these sites, following a seral sequence different from that occurring in fire-origin stands.Key words: terrestrial lichens, pine woodlands, caribou habitat.