Vegetation Ecology of Debris-Covered Glaciers (DCGs)—Site Conditions, Vegetation Patterns and Implications for DCGs Serving as Quaternary Cold- and Warm-Stage Plant Refugia

Abstract

Scientific interest in debris-covered glaciers (DCGs) significantly increased during the last two decades, primarily from an abiotic perspective, but also regarding their distinctive ecology. An increasing body of evidence shows that, given a minimum of debris thickness and sufficient substrate stability, DCGs host surprisingly diverse plant assemblages, both floristically and structurally, despite being obviously cold and in parts also highly mobile habitats. As a function of site conditions, floristic composition and vegetation structure, DCGs represent a mosaic of environments, including subnival pioneer communities, glacier foreland early- to late-successional stages, morainal locations, and locally, even forest sites. On shallow supraglacial debris layers, cryophilous alpine/subnival taxa can grow considerably below their common elevational niche due to the cooler temperatures within the root horizon caused by the underlying ice. In contrast, a greater debris thickness allows even thermophilous plant species of lower elevations to grow on glacier surfaces. Employing the principle of uniformitarianism, DCGs are assumed to have been important and previously undocumented refugia for plants during repeated Quaternary cold and warm cycles. This review and recent study summarize the current knowledge on the vegetation ecology of DCGs and evaluates their potential function as plant habitat under ongoing climate warming.