NEOGLACIAL CLIMATE CONTROL OF SUB-ARCTIC PICEA-ABIES STAND DYNAMICS AND RANGE LIMIT IN NORTHERN SWEDEN

The study focused on the performance of the spruce (Picea abies [L.] K arst.) range limit in northern (subarctic) Sweden during the Neoglacia l period of the Holocene, mainly after the climax of the Little Ice Ag e. Subfossil wood remains suggest that the geographic spruce tree limi t has remained fairly stable for slightly more than the past 2000 C-14 yr. Previous postulates about delayed immigration and continual sprea d are contradicted in favor of a dynamic climate/spruce equilibrium. T he mechanism restricting the spruce distribution was inferred to be se vere annual ground frost characterizing this climatically continental and snow-poor region, which is crossed by the Limit of discontinuous p ermafrost. An extensive (landscape scale) age structure analysis showe d near-exponential population build-up over the past 100 yr or so. Thi s manifested as densification of outlying stands and sparse range limi t advance by some tens of kilometers. These responses clearly related to increased snowfall during the early (December) and late winter (Mar ch). In consequence, annual ground frost and permafrost declined in ge neral, which made the least ground frost prone sites equable for estab lishment and persistent growth (less risk of winter desiccation) of sp ruce. These inferences are strengthened by tendencies for decreased sp ruce regeneration and vitality during the past decades, coincident wit h some exceptionally cold and snow-poor early winters. It is speculate d that the structure and performance of the studied system, i.e. outli ers checked by severe ground frost, is a small-scale analogy to the si tuation preceding the general late Holocene expansion of spruce in Fen noscandia.