Epiphytic Lichens as Indicators of Snow Depth

Abstract

The vertical distributions of Parmelia olivacea and a few other epiphytic lichens on trunks of deciduous trees were studied in relation to maximum snow depth along an oceanic-continental climate gradient in subarctic Scandinavia. The lower limit of P. olivacea, “the Olivacea-limit,” which is usually found above the winter snow surface, showed a high positive correlation with snow depth. This positive correlation also applied to the upper limit of Parmeliopsis ambigua growing on the trunk bases, i.e. “the Parmeliopsis-limit.” Hypogymnia physodes and Parmelia sulcata showed a distribution similar to that of P. olivacea on the continental sites but also occurred below the Olivacea-limit at the oceanic sites above the Parmeliopsis-limit. The distribution of Cetraria sepincola showed no relation to either “limit” and thus to snow cover. The field observations and experiments indicated that P. olivacea can be exposed to snow or ice for 2 mo without any loss of vitality, but will be killed when repeatedly covered for several winters for periods longer than 2 mo. There was no decline in the vitality of thalli of P. olivacea eroded due to experimental exposure to lasting snow and measured as chlorophyll fluorescence. Nor did storage in ice in the laboratory for 2 mo in darkness at −1°C decrease vitality as indicated by the fact that the rate of photosynthesis remained unchanged in P. olivacea and increased in P. ambigua, and respiration rates decreased in both species. It is suggested that the degree of definition of the Olivacea- and Parmeliopsis-limits, i.e. their “sharpness,” is determined by the polishing effects of wind and ice crystals.