Pollen evidence of vegetational change following early European settlement of Monhegan Island, Maine, northeastern U.S.A.

Postsettlemcnt vegetation changes beginning in the early 17th century were studied through comparing stratigraphic peat-pollen data with available historical evidence. The isolation of the site and the relatively long historical record were ideal for the study. Human disturbance of the vegetation was readily identified in the pollen diagram with a contemporaneous increase in sediment mineral matter. The effects were much the same as the changes associated with Neolithic forest clearance in Northern Europe. Settlement resulted in the introduction and expansion of several cultural weeds after grazing and cultivation of Zea mays began on the island in the first decades of the 17th century; Rumex acetosa-acetosella, Ranunculus acris type, Plantago major-media and several new Compositae and Umbelliferae species all appeared at that time. The response of the native species to settlement was varied. Because of the limitations of the palynologic method, the area of cultivated land and detailed kind of agriculture can only be estimated. The data suggest that although agriculture was intensive from time to time, it took place on a very limited local scale; fires, grazing, and lumbering were the major factors affecting natural ecosystems.     

Differences in pollen and macrophytic remains in sediments from various depths in a small kettle-hole lake in southern Finland

Stratigraphical analyses from four locations within the same lake revealed differential dispersal of pollen in sediment, and horizontal movement and focusing of sediment, but revealed only slight differences in pollen and macrofossil assemblages. Between 9,000 and 8,000 B.P., organic sediments focused into the central depth of the basin and no sediment accumulated in the littoral sites in water < 7.5 m deep. From around 5,000 to 4,500 B.P., deposition took place more or less continuously at all four sites. After 1,600 B.P., the marked change in lithology is due to a heavy rise in organic and minerogenic input from the unforested watershed. The littoral cores show that not only does the water depth cause rcdeposition and focusing of sediment, but also the morphometry of the basin. The comparison between macrofossils and pollen, both produced primarily by the same vegetation around the lake, confirmed the reconstruction of local environmental short-term changes which occurred after the clearance of forest vegetation by man.     

Three-dimensional reconstruction of carbon accumulation and CH4 emission during nine millennia in a raised mire

A three-dimensional model, based on numerous vertical and horizontal ¹⁴C datings and GIS simulation from a concentrically domed mire in southern Finland, demonstrates considerable variation in actual (net) rate of carbon accumulation (ARCA) through time. Lateral growth between 9000 and 3000 yr ago accounts for only 25% of the total carbon sequestration, whereas bog formation after ombrotrophication is responsible for the remaining 75%. On the other hand, the most rapid increase in landscape CH₄ flux occurred between 4500 and 3000 yr ago, the period of the fastest horizontal growth. In addition to autecological factors, a climatic shift towards cooler and wetter conditions is a plausible mechanism for maintaining accelerated carbon accumulation.     

Diurnal laminations in the varved sediment of Lake Lovojärvi, south Finland

A man-induced extensive silty layer in the sediment of Lake Lovojärvi, dating back to the year 1960, contained 18 laminations due to rhythmical variations in the size classes of the mineral particles. A good agreement was found between the thicknesses of the successive laminae, and one period in a sequence of arbitrary 'wind sums' calculated from the meteorological statistics of the spring 1960 for periods of winds exceeding 3 m/s. Most of these wind pulses were diurnal; the longest one lasted for five days. The deposition of the layer in early spring was further confirmed through diatom analysis, which revealed within the laminated sequence a diatom succession typical of Lake Lovojärvi immediately after the melting of ice in spring