Shrinking glaciers and ice patches disclose megafossil trees and provide a vision of the Late-glacial and Early post-glacial subalpine/alpine landscape in the Swedish Scandes – review and perspective

Extensive glacier recession has prevailed for almost 100 years in the Scandes and other parts of the world. At the lower fringe and forefields of shrinking alpine glaciers and ice patches, a plethora of ancient tree remnants is recovered. This is presumably the first time of exposure since burialby ice thousands of years ago. These remains represent prior stands of virtually all boreal tree species, currently growing in northern Scandinavia. As a consequence, a previously unexpected and patchily treed high-mountain landscape emerges, in some cases 600-700 m higher than present-day treelines. This difference in treeline positions between then and now (corrected for land uplift) indicates that summer temperatures have declined by about 3 °C since the early Holocenetreeline maximum. Radiocarbon-dating reveals that the age of the tree remnants ranges between c. 16 800 and 2000 cal. yr BP. Initially,the high-mountainpeaks stood out asnunataks in a surrounding for long glaciated landscape at lower elevations. As the ice sheet gradually shrinked, glacier cirques and hollows became filled with tree groves, in a matrix of alpine tundra. In addition to Betulapubescens ssp. czerepanovii , Piceaabies and Pinussylvestris , these high-elevation enclaves contained tree species, previously unknown to such high positions and so early. These are Piceaabies and a species currently considered as exotic to Scandinavia, namely Larixsibirica . In response to gradual climate cooling since the middle Holocene, the tree stands declined and dead trees were eventually entombed by glacier ice, which is currently disintegrating.