925 resultados para Juniperus virginiana


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A Holocene pollen diagram from Kleiner Mochowsee (northern Niederlausitz, East Germany) shows pine as an important constituent of the woodland south of the Schwielochsee. Oak woodland was widespread since the Atlantic. Betula lost its importance at the end of the Preboreal. Fagus is represented continuously in the pollen record since the Atlantic, Carpinus since the Subboreal. However, the two latter tree species remain without great importance throughout the whole pollen record. The poor sandy soils are furthermore reflected by the low values of Corylus during the Boreal, comparable to other records from Berlin and its surrounding area. The 'classical' elm decline could be shown for the Niederlausitz, radiocarbon dates assume a contemporaneous age for this event with other records from northern Germany. Only small-scaled human impact is indicated in prehistoric times, during the migration period it seems to have ceased completely. Later, in the Medieval, deforestation and tillage can be shown. Secale was cultivated since the early Medieval; an accompanying weed flora appeared at the same time. Cultivation of Fagopyrum and Linum usitatissimum could be shown for the late Medieval times.

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Fiekers Busch is a wet alder wood close to Rinteln (southwest of Hannover/West Germany) existing there since about 6 000 or - at the most - 7 500 radiocarbon years. The sandy layers below the peaty sequence date from about 9 000 BP. The pollen diagram shows the basic trends of the postglacial vegetational development. Low pollen frequency and poor pollen preservation do , however, strongly restrict the possibilities to explain the peculiarities of the pollendiagram, especially the high pine and linden values.

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Innerdalen was once a mountain valley (ca. 780 m a.s.l.) with birch forests, bogs and several summer farms. Today it is a 6.5 km**2 artifical lake. In 1980 and 1981 archaeological and palynological investigations were carried out due to the hydroelectric power plans. Radiocarbon dated pollen diagrams from 9 different localities in Innerdalen provide information on a mountain environment which has been exploited to varying degrees by human groups for thousands of years. In the Birch Zone, ca. 9500-8500 years B.P., the deglaciated surface is vegetated by the normal sequence of pioneering species, first show-bed communities, then shrub/dwarf-shrub communities, and finally a birch forest community. In the Pine Zone, ca. 8500-7500 years B.P., the mixed Birch-Pine forest which prevailed at the end of the Birch Zone is replaced by a dense pine forest. The tree limit was higher than it is today. In the Alder Zone, ca. 7500-4000 years B.P., the newly arrived alder gradually succeeded pine, particularily on good soils. This alder forest has a modem analog in the pre-alpine gray alder forests in Norway. In the last part of the Alder Zone, ca. 6000-4000 years B.P., elm and hazel are nominally present on particularily rich soils, marking the edaphic and climatic optimum in Innerdalen. During this time the first evidence of human impact on the vegetation is apparent in the pollen diagrams. At both Sætersetra in the south of the valley and Liabekken in the north, forest clearance and the development of grazed grass meadows is documented, and human impact continues until the present. The Herb Zone, ca. 4000 years B.P. to 1600 A.D., is characterized by the rapid decline of alder. The forest is increasingly open, and bog formation is initiated. The sub-alpine belt of birch forest is established, probably due to the shift to a cooler, moister climate. Human activity can also have influenced the vegetational changes, although at 4 of the localities human activity also is first apparent after the alder decline. Some localities show measurably less human impact on the vegetation ca. 2600-2000 years B.P. Grazing intensity increases ca. 2000 years B.P. At the end of the Herb Zone rye and barley pollen is registered at Sætersetra and Flonan, indicating contact between the grazing activities of Innerdal and grain cultivation activities outside the valley. The Spruce Zone, ca. 1600 A.D. to the present, does not begin synchronously since the presence of long-distance transported spruce pollen at a locality is entirely dependent on the density of the vegetation ie. degree of human impact. The youngest spruce rise is ca. 1500 A.D. at Røstvangen, when summerfarming is initiated. Summerfarming activities in Innerdal produce an increasingly open landscape. Rye and barley pollen at several localities may indicate limited local cultivation, but is more likely long-distance transport via humans and domesticated animals from cultivated areas outside Innerdalen.

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There is a great similarity between pollen types which occur in the early Holocene NE Tibetan pollen spectra and those which are commonly considered to be typical for the Würm Late Glacial period in Central Europe and for the Würm Pleniglacial period in Southern Europe. Evidently, this similarity is due to a remarkable general conformity of plant taxa growing in cold-arid regions of the northern hemisphere. The improvement of the climate and the retreat of the glaciers that commenced at the end of the Würm period had already terminated definitely before 9500 BP. In addition, the climatic situation as well as the vegetation belts must have remained rather constant during the following 3000 yr, i.e. through most parts of the climatic optimum of the Holocene.

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Die untersuchten Schluffe und Kiese sind unter kaltzeitlichen Bedingungen in einem See mit Schwimmpflanzengesellschaften abgelagert worden. Zur Sedimentationszeit gab es in der Umgebung des Sees eine tundrenartige Vegetation, die auch Steppenarten enthielt.

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Site details: The raised bog Fláje-Kiefern (50°429N, 13°329 E; 760 m a.s.l.; size ca. 500x500 m) lies in the Krusné Hory Mountains (Erzgebirge), Czech Republic, about 10 km from Georgenfelder Moor in Germany. Hejny and Slavík (1988) described the phytogeographic region of the Krusne Hory Mountains as 'a region of mountain flora and vegetation, with thermophilous species largely missing. In the natural forests, conifers, especially spruce (Picea excelsa) prevail. The deforested areas have been converted into meadows and pastures'. The climate is cool with annual average temperatures of about 5°C and annual precipitation of about 900 mm. The bedrock is Precambrian crystallinicum.

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A pollen diagram from the Ahlequellmoor in the Solling area shows the history of vegetation and settlement over the last 7,800 years. In the early Atlantic period mixed deciduous forest with mainly Tilia together with Ulmus and Quercus grew in the area. In the late Atlantic period Quercus became most abundant. Fagus spread in the Sub-boreal period at about 2700 B.C. Since ca. 900 B.C. the Solling was covered by beech forests with some oak. In prehistoric times woodland grazing is indicated. Only in Medieval times are two settlements in the vicinity of the Ahlequellmoor reflected in the pollen diagram. The earlier one is dated to about A.D. 750-1020, and may be connected with the former Monastery of Hethis, which is thought to have existed close to the fen from A.D. 815 to 822. The second Medieval settlement dates to the 11th-12th century. The large-scale woodland destruction of late Medieval and modern times is not clearly visible. The silvicultural measures of the last 200 years are reflected by increasing values of spruce and grassland taxa.

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Pliocene vegetation dynamics and climate variability in West Africa have been investigated through pollen and XRF-scanning records obtained from sediment cores of ODP Site 659 (18°N, 21°W). The comparison between total pollen accumulation rates and Ti/Ca ratios, which is strongly correlated with the dust input at the site, showed elevated aeolian transport of pollen during dusty periods. Comparison of the pollen records of ODP Site 659 and the nearby Site 658 resulted in a robust reconstruction of West African vegetation change since the Late Pliocene. Between 3.6 and 3.0 Ma the savannah in West Africa differed in composition from its modern counterpart and was richer in Asteraceae, in particular of the Tribus Cichorieae. Between 3.24 and 3.20 Ma a stable wet period is inferred from the Fe/K ratios, which could stand for a narrower and better specified mid-Pliocene (mid-Piacenzian) warm time slice. The northward extension of woodland and savannah, albeit fluctuating, was generally greater in the Pliocene. NE trade wind vigour increased intermittently around 2.7 and 2.6 Ma, and more or less permanently since 2.5 Ma, as inferred from increased pollen concentrations of trade wind indicators (Ephedra, Artemisia, Pinus). Our findings link the NE trade wind development with the intensification of the Northern Hemisphere glaciations (iNHG). Prior to the iNHG, little or no systematic relation could be found between sea surface temperatures of the North Atlantic with aridity and dust in West Africa.