NEW AND FIRM EVIDENCE FOR MIDHOLOCENE APPEARANCE OF PICEA-ABIES IN THE SCANDES MOUNTAINS, SWEDEN

1 A subalpine clonal population of Picea abies in the Scandes Mountains (Sweden) was analysed with respect to age structure, height and radial growth, foliage vigour and radiocarbon dates of subfossil wood fragments. 2 A tree-ring chronology yielded consistently low annual increments from AD 1600 to the mid-1800s. Subsequently, radial growth, initiation of new stems and height growth increased in accord with climate warming and possibly deeper snow cover. The growth form changed from krummholz to erect tree-size. During the past c. 50 years growth has declined and supra-nival stems have eroded. The reason is climate cooling mediated by the complex temperature/snow cover/ground frost, which appears as a critical determinant of the Holocene Picea spread. 3 Subfossil Picea wood was dated to c. 4800-4700 radiocarbon years sp (two dates), i.e. Picea grew here more than 2000 years prior to inferences from pollen data. Obviously, stray finds of pollen may represent local presence and it is hypothesized that Picea immigrated to specific microhabitats even earlier than the date established here, possibly soon after the regional deglaciation. Much later it could spread regionally as climate gradually became less seasonal, damper and more snow-rich, in response to orbital forcing of insolation. 4 Early immigration, well before local or regional dominance, precludes migrational lag and rather suggests that in a landscape perspective a dynamic equilibrium between Picea abundance and climate has existed for most of the Holocene. The elevational range-limit, however, may have been out-of-phase with climate for centuries or millennia, tuned to climate mainly by phenotypic responses.