The natural holocene vegetation development and the introduction of agriculture in northern Norrland, Sweden studies of soil, peat and especially varved lake sediments

University dissertation from Umeå : Umeå Universitet

Abstract: The Holocene vegetation history of northern Norrland was studied by pollen analysis of sediement, peat and soil samples, with the aim to improve our knowledge about vegetation development in northern Norrland, and also about the history of man and the introduction of agriculture in the area. Earlier made pollen analyses from the four northernmost provinces were summarized and a series of new analyses from northern Norrland added. Pollen anlyses were conducted on sediment and peat profiles from four sites in the Luleälv valley, in Norrbotten, and from Kassjön in coastal Västerbotten. Furthermore, the hypothesis was tested that pollen analysis of thin mor humus soils could be used to trace and identify ancient cultivated fields.When the interior parts of the Luleälv valley were deglaciated about 9500 BP, an open ecosystem formed dominated by shrubs and dwarf-shrubs. A few hundred years later Betula and Pinus invaded and rapidly formed forests, and by 9000 BP Alnus had immigrated and become common in most of Norrland. With climatic improvement Betula and Alnus increased in abundance, and nemoral broad-leaved trees colonized from south to north: between 6000-3500 BP Ulmus and Corvlus had become common as far north as Västerbotten. In Norrbotten, however, Betula and Alnus were the dominant deciduous trees.Around 3400 BP Picea abies reached the coast of Norrland from Finland, established itself and within 300 years became the major forest tree along a coastal zone. It occupied the moist, fine sediment substrates in those areas which earlier had been mainly dominated by Alnus and Betula. Climatic deterioration resulted in a steady retreat of the more southerly forest elements, and by 2000 BP only small, remnant stands at isolated sites were left. Over the last 2000 years little natural change has occurred in the forest vegetation.Man invaded the area soon after the deglaciation. These first occupants were hunters and fishermen, however, and their impact on the vegetation development was minor and restricted to small camp clearings. Not until an agricultural economy became established, did the influence of man become pronounced. In coastal Västernorrland and Västerbotten, traces of agriculture and animal husbandry occurred between 4700-2500 BP, but these first cereal cultivations were temporary, short-lived and occurred primarily at coastal sites. In those areas, permanent cultivation developed due to changed settlement structure during the first centuries AD. In the Luleälv valley in Norrbotten, cereal cultivation and animal husbandry was introduced between 500-1000 AD, although the hunter/gatherer economy continued to dominate, as it did in most of interior Norrland. Concomitant with the general agricultural expansion in Västernorrland and Västerbotten between 1000-1200 AD, permanent fieldcultivation developed in the coastal parts of the Luleälv valley. In the interior of northern Norrland, however, agriculture did not become important until the 17th-19th centuries.