Lichen Mortality Due to Late-Lying Snow: Results of a Transplant Study

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Abstract
Lines of lichen-covered rocks were installed on the floors of two semipermanent snowpatches above timberline in the Colorado Front Range [USA]. All Rhizocarpon subgenus Rhizocarpon thalli died within 5 to 8 yr where the average annual duration of snowcover exceeded 40.3 to 42.7 wk. Thalli of snow-tolerant Rhizocarpon species (especially R. riparium) survived for the duration of the study where snow cover was less persistent, and where meltout occurred by 1 July in occasional years. Lichen mortality is attributed to depletion of thallus carbon reserves in late spring and summer, when meltwater was continuously available at the base of the snowpack, light penetration was negligible, and thalli respired but were unable to photosynthesize. Fast-growing lichen species such as Umbilicaria virginis and Xanthoria elegans were less tolerant of late-lying snow than were slow-growing species such as Lecidea atrobrunnea and R. riparium; species-related differences in susceptibility to snowkill make interspecific diameter ratios unreliable. The lichen-free areas that surround modern Front Range snowbanks are products of the 1950s, when snow accumulation was greater than today. Earlier episodes of massive lichen kill on the floors of Front Range alpine valleys may have resulted from warm(0.degree. C) subnival winter temperatures rather than from very late-lying general snow cover, as was previously believed.