Norway spruce present in the Scandes Mountains, Sweden at 8000 BP: New light on holocene tree spread

Norway spruce (Picea abies (L.) Karst.) is the dominant boreal tree in Fennoscandia, but important aspects of its Holocene history are unknown. Subfossil wood fragments underneath living subalpine clonal groups and in a tree-less mire in the Scandes Mountains of Sweden now firmly demonstrate that spruce grew here as early as c. 8000 BP. That is more than 5000 years before inferences of local presence have been made from pollen data. Recurrent speculation of migrational lags can now be refuted in favour of a climate-plant equilibrium prevailing throughout much of the Holocene. After adjustment for glacio-isostatic land-uplift, the tree-limit has retreated about 120 m in altitude since 8000 BP in response ultimately to climate cooling. In contrast, the range-limit remained almost stable. The relatively late east-west progression of Picea as a regional dominant in northern Fennoscandia during the Holocene is inferred to relate to various ecological effects of decreased climatic seasonality, foremost increased snow cover. The results provide new perspectives on Fennoscandian palaeoecology and the method of vegetation reconstruction from pollen analysis in general.