Forest edge-induced damage of cephalo- and cyanolichens in northern temperate rainforests of British Columbia

Abstract

Retention of trees after logging is a method of preserving epiphytic lichens; however, epiphytes’ responses to logging disturbance are insufficiently known. We aimed to characterize four viability measures — effective PSII yield (ΦPSII; a proxy for photosynthesis), maximal photosystem II efficiency (FV/FM; a proxy for photoinhibition), chlorophyll a content, and chlorophyll a/b ratio — and the functional parameter specific thallus mass (STM; a proxy for water storage) in sympatric populations of two old-growth lichens (Lobaria retigera (Bory) Trevisan and Lobaria oregana (Tuck.) Müll. Arg.) and the less old-growth dependent Lobaria pulmonaria (L.) Hoffm. along recently logged forest edge gradients within retained forest patches. All species experienced substantially reduced chlorophyll contents near edges, whereas ΦPSII was lower in the two old-growth lichens than in L. pulmonaria. STM, and thus lichen water storage, did not respond to logging, probably because chlorophyll degradation reduced the carbon gain required for necessary acclimation. Reported edge effects on lichen viability were so strong that most of the epiphytic lichens in the retained forest patches were affected. Measured viability variables improved linearly with distances up to ≈120 m from the edge. To avoid logging-induced adverse impacts on the threatened epiphytic lichens of these old-growth rainforests, there is a need to retain forest patches wider than 240 m.