PALEOECOLOGICAL, BIOGEOGRAPHICAL AND PALEOCLIMATOLOGICAL IMPLICATIONSOF EARLY HOLOCENE IMMIGRATION OF LARIX SIBIRICA LEDEB. INTO THE SCANDES MOUNTAINS, SWEDEN

For the first time, Holocene macroremains (cones and wood) of Larix si birica Ledeb., radiocarbon dated between 8700 and 7500 sp, have been r ecovered from two sites in the Scandes Mountains of Sweden. The sites are separated by >300 km and lie in the present subalpine and low alpi ne belts, respectively. Existing pollen-stratigraphical records have n ot suggested the presence of Larix in the Holocene beyond its present range, i.e. >1000 km to the east in Russia. Hence, the pollen analytic al method should be used more cautiously when inferring subcontinental -continental biogeographical dynamics. It appears that Larix immigrate d rapidly by long-distance jump dispersal soon after the deglaciation. The same pattern has emerged for Picea abies (L.) Karst. and some the rmophilous broadleaved tree species. This might be a more general mech anism for tree spread during the early Holocene. Step-wise migration a nd migrational lags could be quire unimportant elements within tree pa laeobiogeography. This increases the prospects fcr interpretation of l ongterm 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 Fennosca ndia could have been similar to, or slightly colder than those of toda y. This contention conflicts with previously published simulations usi ng General Circulation Models, pollen-climate response surfaces and ot her retrospective devices, which suggest a strongly oceanic climate wi th winters >2 degrees C warmer than present.