A history of vegetation and fire, 6,600 B.P. to present, County Sligo, western Ireland

Dodson, John R. & Bradshaw, Richard H. W. 1987 06 01: A history of vegetation and fire, 6,600 B.P. to present, County Sligo, western Ireland. Boreas , Vol. 16, pp. 113–123. Oslo. ISSN 0300–9483.
Two lake sites on metamorphic rocks with small catchments and one mor humus deposit have been analysed to assess the relative influences of fire, man and climate upon the regional and local vegetation of the Lough Gill region of County Sligo. The vegetation of the area was dominated by mixed woodland from 6,600 B.P. to 600 B.P. The first evidence of human impact on the forests was around 5,400 B.P. in the form of clearance for pasture. The intensity of human impact varied between sites, and there were periods of forest recovery as well as decline. From 600 B.P. widespread forest destruction took place, and pasture with heathland became predominant. Pinus sylvestris had a major presence until about 5,400 B.P. It declined from this time and had a patchy distribution by 2,000 B.P. The decline of Pinus was linked with the expansion of treeless peatland in what are presumed to be wet periods, and Pinus recovery in drier periods. Fire may have encouraged the spread of heathland at the expense of Pinus . Arbutus unedo pollen was found at Slish Lake as early as 1,900 B.P., suggesting that it is native to this area. Isolated trees survive today at woodland edges. Charcoal particles occurred in all the profiles. Fire was particularly associated with heathland communities, and may have been used as a management tool to improve grazing conditions. Some of the phases of woodland decline correlate strongly with charcoal input suggesting forest destruction by fire.     

Petrogenesis and Significance of the Jebel Dumbier Alkaline-Carbonatite Complex from North Margin of Nuba Mountains, Sudan

<正>1 Introduction Scientific study of the geology and mineral resources in Sudan is rather limited.Jebel Dumbier is the first identified carbonatite-bearing alkaline complex in Sudanby El SharkawiEl Raba'a in 1973.It is located in Northern Kordofan Province on the northeastern margin of the Nuba Mountains.The complex exposed as small     

Qualitative interpretation of remotely sensored data as a key to mapping vegetation patterns in the Western Sudan

Data capabilities of satellites remote sensor systems are briefly discussed. Monthly remotely sensored data of NIMBUS 3 meteorological satellite over parts of the Sudan, West of Lake Chad in Africa, using the HRIR — High Resolution Infra Red Radiometer (sensing between 0.7–1.3 u wavelength) are used to study the monthly shifts in the vegetation boundaries for this area. These shifts are shown to be caused by changes in soil moisture content which is controlled by the prevailing meteorological conditions in the area during the months.     

European vegetation history: Palaeovegetation maps from pollen data - 13 000 yr BP to present

Pollen data are the most important source of information with respect to late Quaternary vegetation history. Broad-scale palaeovegetation patterns have been subjectively inferred from mapped pollen data by previous authors. In this study, multivariate classification was applied to European pollen data for the last 13 000 yr. The resulting clusters are mapped at millennial intervals and can be equated with vegetation units. The maps portray the changing vegetation of Europe since the last glacial. They reveal the impermanence of the assemblages of species that ecologists recognise as communities. The dominant patterns in the maps also change through time, indicating important changes in palaeoenvironmental conditions and in the alignment of major environmental gradients. Human impact upon European vegetation history is seen to be relatively unimportant when the vegetation is viewed at a continental scale.     

Holocene history of fire,vegetation and land use from the central Pyrenees (France)

Located on a mountain pass in the west-central Pyrenees, the Col d'Ech peat bog provides a Holocene fire and vegetation record based upon nine ¹⁴C (AMS) dates. We aim to compare climate-driven versus human-driven fire regimes in terms of frequency, fire episodes distribution, and impact on vegetation. Our results show the mid-Holocene (8500–5500 cal yr BP) to be characterized by high fire frequency linked with drier and warmer conditions. However, fire occurrences appear to have been rather stochastic as underlined by a scattered chronological distribution. Wetter and colder conditions at the mid-to-late Holocene transition (4000–3000 cal yr BP) led to a decrease in fire frequency, probably driven by both climate and a subsequent reduction in human land use. On the contrary, from 3000 cal yr BP, fire frequency seems to be driven by agro-pastoral activities with a very regular distribution of events. During this period fire was used as a prominent agent of landscape management.     

Petrogenesis of a Neoproterozoic magmatic arc hosting porphyry Cu-Au mineralization at Jebel Ohier in the Gebeit Terrane,NE Sudan

The ca. 730 Ma porphyry Cu-Au deposit at Jebel Ohier in the Red Sea Hills of northeastern Sudan represents a rare example of a preserved Neoproterozoic magmatic-hydrothermal system which bears many similarities to major mineral-hosting (‘productive’) Tertiary–Cenozoic porphyries in circum-Pacific metallogenic belts. Petrographic, lithogeochemical and Sm-Nd isotope systematics confirm that the deposit formed in a supra-subduction setting and during the constructional stage of an evolving intra-oceanic magmatic arc. The calc-alkaline melts were sourced predominantly from juvenile reservoirs and received comparatively little input from continental-character material. Comparison with igneous rocks from barren intrusions elsewhere in the region point to the absence of major crustal breaks but indicate that the ore-forming granodiorite-dacite porphyry complex at Jebel Ohier is the result of ‘abnormal’ and prolonged multi-phase arc plutonism. This process involved the formation of relatively hydrous and oxidized melts via the fractionation of magmas, which possibly had ponded at the bottom of the thickening lithosphere for a protracted period prior to their ascent. The tectonic trigger for the emplacement of the productive pluton into a pre-existing volcanic edifice at Jebel Ohier remains unconstrained. Preservation of what is considered the first documented porphyry Cu-Au deposit in the NE African portion of the Arabian Nubian Shield can probably be related to the accretion of the magmatic arc to a stable continental margin within a few million years of mineralization, thus enabling the deposit to escape excessive uplift, erosion and structural dismemberment.     

Holocene vegetation history of the Okanogan Valley,Washington

Haploxylon pine(s) and Artemisia dominated the initial vegetation in front of the receding Okanogan Lobe until ca. 10,000 yr B.P., as revealed by two pollen records in north-central Washington. After 10,000 yr B.P. the macroclimate became warmer throughout the Okanogan drainage as diploxylon pines and Artemisia increased. The Mount Mazama eruption at ca. 6700 yr B.P. is recorded as two stratigraphically separate and petrographically distinct tephra units at Bonaparte Meadows. While there are apparent short-term changes in the vegetation coincident with the ashfall(s), Artemisia continues to dominate the Okanogan Valley until ca. 5000 yr B.P. By 4700 yr B.P. the modern vegetation, dominated by Pseudotsuga menziesii, had become established around Bonaparte Meadows.     

Quaternary vegetation history of the Mississippi embayment

Nonconnah Creek, located in the loess-mantled Blufflands along the eastern wall of the Lower Mississippi Alluvial Valley in Tennessee displays a sedimentary sequence representing the Altonian Substage through the Woodfordian Substage of the Wisconsinan Stage. The site has a biostratigraphic record for the Altonian and Farmdalian Substages that documents warm-temperate upland oak-pine forest, prairie, and bottomland forest. At 23,000 yr B.P., white spruce and larch migrated into the Nonconnah Creek watershed and along braided-stream surfaces in the Mississippi Valley as far as southeastern Louisiana. The pollen and plant-macrofossil record from Nonconnah Creek provides the first documentation of a full-glacial locality in eastern North America for beech, yellow poplar, oak, history, black walnut, and other mesic deciduous forest taxa. During the full and late glacial, the Mississippi Valley was a barrier to the migration of pine species, while the adjacent Blufflands provided a refuge for mesic deciduous forest taxa. Regional climatic amelioration, beginning about 16,500 yr B.P., is reflected by increases in pollen percentages of cooltemperate deciduous trees at Nonconnah Creek. The demise of spruce and jack pine occurred 12,500 yr B.P. between 34° and 37° N in eastern North America in response to postglacial warming.     

Land use history and status of land desertification in the Heihe River basin

An analysis, over historical times, of the influence of natural factors such as climate, geological activity, existing landforms, and the activity of aeolian sands on the desertification of oases and other lands in the Heihe River basin of northwestern China revealed that desertification occurred more or less quickly according to whether the prevailing climate was cold or warm, respectively. In the 1990s, the area of desertified lands in the lower reaches of the Heihe River (Ejin region) was 29.1% greater than in the mid 1980s. However, the rate of desertification in the middle reaches of the Heihe River basin was relatively slower, only 9.4% from 1949 to 1990 (or 0.27% per year). Since 1990, the rate of desertification has been stable. By 2000, the total area of land desertification in the mid to lower reaches of the Heihe River basin was 13,508.4 km², or 11.8% of the region monitored. Of the total land desertification area, the regions of Linze, Gaotai, Sunan, Jiuquan, Jia Yuguan, and Jinta accounted for 1.70, 1.71, 1.43, 0.85, 0.28, and 9.39%, respectively, whereas the Ejin region’s 11,434.64 km² accounted for 84.65%, indicating that land desertification in the lower Heihe River basin was particularly severe. The causes responsible for the occurrence and development of land desertification in the Heihe River basin were analyzed.     

The Holocene vegetation history of the Arfon Platform, North Wales, UK

Detailed pollen, charcoal and loss on ignition profiles were analysed from Llyn Cororion, North Wales, UK. The chronology was based on 11 radiocarbon dates. This site is particularly important for this region because its high-resolution record improves the spatial and temporal resolution of records of Holocene vegetation change in an area characterized by a highly variable environment. An early Holocene phase of Juniperus-Betula scrub was succeeded by Betula-Corylus woodland. Quercus and Ulmus were established by c. 8600 ¹⁴C yr BP, with Pinus dominating at c. 8430 ¹⁴C yr BP. Local disturbance then allowed the spread of Alnus; Tilia was a common component of the forest by 5650 ¹⁴C yr BP. Charcoal and pollen records suggest that by c. 2600 ¹⁴C yr BP there was progressive deforestation, increased use of fire and spread of grassland; the first cereal grain was recorded at c. 2900 ¹⁴C yr BP. Compared with data from upland Snowdonia, the results show that within a topographically diverse region there were significant local variations in forest composition. These variations developed as a response to interactions between many environmental parameters and were further complicated by the influence of human activity. In an area such as North Wales it is therefore unlikely that one site can be representative of regional Holocene vegetational development. The site is additionally important because it contributes to the data available for meta-analyses of environmental change in the North Atlantic region, particularly as detailed pollen diagrams from coastal lake sites around western Europe are rare.     

Holocene vegetation history of the Prince William Sound region, south-central Alaska

Vegetation history during the Holocene is interpreted from the pollen and sedimentary records of nine sections of peat deposits located in sedge tundra at sites in the northern and northwestern parts of the Prince William Sound region. Basal radiocarbon ages of the deposits are between 10,015 and 580 yr B.P. Modern surface pollen data from these and 25 additional sites, ranging from lowlands to an altitude of 675 m in the alpine tundra, were used to aid in the interpretation of the fossil records. Both frequency and influx pollen diagrams of the oldest section disclose a sequence of communities beginning with sedge tundra, containing thickets of willow and alder, followed by alder, which became predominant at about 8300 yr B.P. Later, alder declined, and an inferred growth of sedge tundra and the establishment of colonies of mountain hemlock and Sitka spruce with some western hemlock occurred about 2680 yr B.P. Finally, regrowth of sedge tundra accompanied by the development of forest communites took place over the past 2000 yr. The influence of glacier advances on the vegetation in the fjords occurred during Neoglacial episodes dated at 3200–2500 yr B.P. and during recent centuries. Regional Holocene tectonic activity was also an influential factor, especially at the time of the 1964 earthquake.     

Late Pleistocene and Holocene vegetation history of the Bale Mountains,Ethiopia

A sediment core recovered from Garba Guracha, a glacial lake at 3950 m altitude in the Bale Mountains of Ethiopia, at the boundary of the Ericaceous and Afroalpine vegetation belts, provides a 16,700-year pollen record of vegetation response to climatic change. The earliest vegetation recorded was sparse and composed mainly of grasses, Amaranthaceae–Chenopodiaceae and Artemisia, indicating an arid climate. At 13,400 cal BP, Amaranthaceae–Chenopodiaceae pollen declined sharply and Cyperaceae increased, suggesting a change to moister conditions. The Younger Dryas interval is represented by a small increase in Artemisia and reduced Cyperaceae, indicating aridity. Just after the start of the Holocene (11,200 cal BP), the upper altitudinal limit of the Ericaceous belt rose, and woody Ericaceous vegetation extended across the Sanetti plateau, in response to increased moisture and temperature. The marked change from clastic to organic lake sedimentation at this time reflects the increase in woody vegetation cover in the lake catchment, accompanied by soil stabilisation, and increased leaf litter and soil humus content. From about 6000 cal BP, and especially after 4500 cal BP, mid-altitude dry Afromontane Juniper–Podocarpus forests developed on the northern slopes of the mountains in response to reduced rainfall in a shortened wet season. Erica shrub and forest decreased in area and altitude, and the Afroalpine ecosystem expanded on the plateau. Podocarpus declined from about 2000 cal BP, as Juniperus increased to its present dominance at 2500–3300 m altitude. Human impact on the high-altitude Afroalpine and Ericaceous vegetation has been relatively minor, confirming that the endemic biodiversity of the Ethiopian mountains is a legacy of natural Holocene vegetation change, following repeated expansion and contraction of the upland ecosystems during the Quaternary.     

Postglacial vegetation, fire, and climate history of the Siskiyou Mountains, Oregon, USA

The forests of the Siskiyou Mountains are among the most diverse in North America, yet the long-term relationship among climate, diversity, and natural disturbance is not well known. Pollen, plant macrofossils, and high-resolution charcoal data from Bolan Lake, Oregon, were analyzed to reconstruct a 17,000-yr-long environmental history of high-elevation forests in the region. In the late-glacial period, the presence of a subalpine parkland of Artemisia, Poaceae, Pinus, and Tsuga with infrequent fires suggests cool dry conditions. After 14,500 cal yr B.P., a closed forest of Abies, Pseudotsuga, Tsuga, and Alnus rubra with more frequent fires developed which indicates more mesic conditions than before. An open woodland of Pinus, Quercus, and Cupressaceae, with higher fire activity than before, characterized the early Holocene and implies warmer and drier conditions than at present. In the late Holocene, Abies and Picea were more prevalent in the forest, suggesting a return to cool wet conditions, although fire-episode frequency remained relatively high. The modern forest of Abies and Pseudotsuga and the present-day fire regime developed ca. 2100 cal yr B.P. and indicates that conditions had become slightly drier than before. Sub-millennial-scale fluctuations in vegetation and fire activity suggest climatic variations during the Younger Dryas interval and within the early Holocene period. The timing of vegetation changes in the Bolan Lake record is similar to that of other sites in the Pacific Northwest and Klamath region, and indicates that local vegetation communities were responding to regional-scale climate changes. The record implies that climate-driven millennial- to centennial-scale vegetation and fire change should be considered when explaining the high floristic diversity observed at present in the Siskiyou Mountains.     

Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska

An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ∼12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (∼12,900 cal yr BP) was pine woodland (Pinus contorta) with alder (Alnus), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ∼12,240 cal yr BP, Sitka spruce (Picea sitchensis) began to colonize the island while pine woodland declined. By ∼11,200 cal yr BP, mountain hemlock (Tsuga mertensiana) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ∼10,180 cal yr BP, when western hemlock (Tsuga heterophylla) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ∼7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars (Chamaecyparis nootkatensis, Thuja plicata) appeared on Mitkof Island during the late Holocene.     

Holocene vegetation, fire and climate history of the Sawtooth Range, central Idaho, USA

The paucity of low- and middle-elevation paleoecologic records in the Northern Rocky Mountains limits our ability to assess current environmental change in light of past conditions. A 10,500-yr-long vegetation, fire and climate history from Lower Decker Lake in the Sawtooth Range provides information from a new region. Initial forests dominated by pine and Douglas-fir were replaced by open Douglas-fir forest at 8420 cal yr BP, marking the onset of warmer conditions than present. Presence of closed Douglas-fir forest between 6000 and 2650 cal yr BP suggests heightened summer drought in the middle Holocene. Closed lodgepole pine forest developed at 2650 cal yr BP and fires became more frequent after 1450 cal yr BP. This shift from Douglas-fir to lodgepole pine forest was probably facilitated by a combination of cooler summers, cold winters, and more severe fires than before. Five drought episodes, including those at 8200 cal yr BP and during the Medieval Climate Anomaly, were registered by brief intervals of lodgepole pine decline, an increase in fire activity, and mistletoe infestation. The importance of a Holocene perspective when assessing the historical range of variability is illustrated by the striking difference between the modern forest and that which existed 3000 yr ago.     

X-ray investigations related to the shock history of the Shergotty achondrite

X-ray diffraction techniques were employed to evaluate the shock stress suffered by naturally shocked materials from the Shergotty achondrite. Experimentally shocked augite and enstatite, subjected to pressures from 22 to 60 GPa, served as standards. The Shergotty pyroxenes reveal formation of continuous diffraction rings, line broadening, preferred orientation of small scale diffraction domains, and other evidence of substantial lattice disorder; they are hybrids between single crystals and fine-grained, random powders as revealed by Debye-Scherrer techniques. As expected from optical studies related to the degree of mosaicism, which is not sensitively related to peak pressures up to 70 GPa, the pyroxene lattice is very resistant to shock damage on smaller scales also as revealed by Debye-Scherrer and powder difractometer X-ray techniques. While measurable lattice disaggregation and progressive fragmentation occurs up to approximately 25 GPa, little additional damage is suffered from 30 to 60 GPa. Thus, pressure calibration of naturally shocked pyroxenes via optical and x-ray methods continues to be difficult.Powder diffractometer scans on pure maskelynite fractions of Shergotty reveal small amounts of still coherently diffracting plagioclase. Future studies should clarify whether such material, possibly of small size and scattered throughout many maskelynite grains, is responsible for the unusually high refractive indices reported for the diaplectic feldspar glasses of Shergotty.     

A history of fire and vegetation in northeastern Minnesota as recorded in lake sediments

The record of charcoal in lake sediments indicates that fire has always been an important ecological factor in the forest history of northeastern Minnesota. The annually laminated sediments of Lake of the Clouds permit precise dating of the charcoal peaks and record the changes in the influx of various pollen types. A detailed record of the past 1000 yr shows that the average frequency of fire is approximately 60–70 yr, with a range of about 20–100 yr. The amount of charcoal in sediments dating between 1000-500 y.a. is consistently higher than that for the last 500 yr, although the fire frequency for the two periods was not appreciably different. Pollen analysis shows no change or only short-term changes in the percentages of major pollen types following charcoal peaks.     

Middle to Late Pleistocene vegetation history and climatic changes at Lake Kopais, Southeast Greece

This study presents a detailed vegetation history of Lake Kopais, Southeast Greece based on pollen analysis of a 120 m-long sediment core. The record extends from the Holocene back to Oxygen Isotope Stage 11, and it gives a detailed history of Mediterranean evergreen woodlands during the last 500 ka. Vegetation of glacials consisted of open steppe with Chenopodiaceae and Artemisia associated with Tubuliflorae and other herbs, while that of interglacials was dominated by temperate Quercus forest. The Last Interglacial (Substage 5e) shows a complete vegetation succession starting with Juniperus and Betula, followed by deciduous oak and ending with Pinus and Abies. Wild olive is abundant in Substages 11c and 5e, suggesting very warm climatic conditions in Stage 11. Stages 9 and 7 were significantly cooler than 11 and 5e. The Pterocarya occurrence near the bottom of the core provides a possible equivalent of the Holsteinian Interglacial.     

Late Quaternary history of Washington Land, North Greenland

During the last glacial stage, Washington Land in western North Greenland was probably completely inundated by the Greenland Ice Sheet. The oldest shell dates from raised marine deposits that provide minimum ages for the last deglaciation are 9300 cal. yr BP (northern Washington Land) and 7600 cal. yr BP (SW Washington Land). These dates indicate that Washington Land, which borders the central part of Nares Strait separating Greenland from Ellesmere Island in Canada, did not become free of glacier ice until well into the Holocene. The elevation of the marine limit falls from 110 m a.s.l. in the north to 60 m a.s.l. in the southwest. The recession was followed by readvance of glaciers in the late Holocene, and the youngest shell date from Neoglacial lateral moraines north of Humboldt Gletscher is 600 cal. yr BP. Since the Neoglacial maximum, probably around 100 years ago, glaciers have receded. The Holocene marine assemblages comprise a few southern extralimital records, notably of Chlamys islandica dated to 7300 cal. yr BP. Musk ox and reindeer disappeared from Washington Land recently, perhaps in connection with the cold period that culminated about 100 years ago.