SPREAD OF BROAD-LEAVED TREES IN ESTONIA

Abstract

The spread of broad-leaved trees ( Ulmus, Tilia, Quercus, Fraxinus, Carpinus, and Fagus) is reviewed on the basis of 46 radiocarbon dated pollen diagrams from lake and mire sediments from Estonia. Ulmus immigrated into Estonia in the second half of the Pre-Boreal, expanded between 9000 and 7800 BP, and reached its maximum values 7900-4200 BP. The immigration of Tilia began between 8800 and 6200 BP; it expanded at 8200-5200 BP, and culminated between 7200 and 4000 BP. Quercus was the next tree to arrive in Estonia, about 7900-7500 BP. Oak spread between 6800 and 4000 BP, with a maximum intermittent between 4200 and 3100 BP. Fraxinus was first recorded about 6500 BP from East Estonia. Carpinus is a late immigrant which reached Estonia in the Sub-Boreal. Comparison of the immigration and expansion of elm, lime, and oak manifests their different response to climate, with elm forest being most broadly distributed between 9000 and 7000 BP, lime between 7000 and 4000 BP (forming then up to 30% of the total forest area), and oak between 4000 and 3500 BP. Elm showed a very rapid colonization from the south; the immigration of lime was more time-transgressive and took place from the south and east. Oak immigrated from the southwest and, in contrast to elm, spread very slowly. The broad-leaved forest reached its maximum density in the second half of the Atlantic and at the beginning of the Sub-Boreal. A gradual retreat of thermophilous trees started with the elm decline at about 5500- 5000 BP, which was quite asynchronous, being caused by the combination of climate deterioration, anthropogenic forest clearances, and fungal diseases.