Palaeoecological, biogeographical and palaeoclimatological implications of early Holocene immigration of Larix sibirica Ledeb. into the Scandes mountains, Sweden

For the first time, Holocene macroremains (cones and wood) of Larix sibirica Ledeb., radiocarbon dated between 8700 and 7500 sp, have been recovered from two sites in the Scandes Mountains of Sweden. The sites are separated by >300 km and lie in the present subalpine and low alpine belts, respectively. Existing pollen-stratigraphical records have not suggested the presence of Larix in the Holocene beyond its present range, i.e. >1000 km to the east in Russia. Hence, the pollen analytical method should be used more cautiously when inferring subcontinental-continental biogeographical dynamics. It appears that Larix immigrated rapidly by long-distance jump dispersal soon after the deglaciation. The same pattern has emerged for Picea abies (L.) Karst. and some thermophilous broadleaved tree species. This might be a more general mechanism for tree spread during the early Holocene. Step-wise migration and migrational lags could be quire unimportant elements within tree palaeobiogeography. This increases the prospects fcr interpretation of longterm and large-scale changes in plant cover performance in terms of expansion/decline relative to climatic change. Today, Larix sibirica prospers in continental climates with extremely cold winters, thus it is reasonable to infer that early-Holocene winters in western Fennoscandia could have been similar to, or slightly colder than those of today. This contention conflicts with previously published simulations using General Circulation Models, pollen-climate response surfaces and other retrospective devices, which suggest a strongly oceanic climate with winters >2 degrees C warmer than present.