The vegetation history of an Amazonian domed peatland

The peatland pole forests of the Pastaza-Marañón Foreland Basin (PMFB), Peru, are the most carbon-dense ecosystems known in Amazonia once below ground carbon stores are taken into account. Here we present the first multiproxy palaeoenvironmental record including pollen data from one of these peatlands, San Jorge in northern Peru, supported by an age model based on radiocarbon and 210Pb dating. The pollen data indicate that vegetation changes during the early phases of peat initiation resulted from autogenic succession in combination with fluvial influence. The overall pattern of vegetation change is not straightforward: the record does not reflect a process of unidirectional, progressive terrestrialization, but includes a reversal in the succession and vegetation transitions, which omit predicted successional phases. This complexity is similar to that seen in the only other existing pollen record from a PMFB peatland, at Quistococha, but contrasts with peat records from Panama and Southeast Asia where successional patterning appears more predictable. Our dating results provide the first evidence from a PMFB peatland that peat accumulation may have been discontinuous, with evidence for reduced rates of peat accumulation, or a possible hiatus, around 1300–400 cal yr BP. An ecological shift from open lake to palm swamp occurs at this time, possibly driven by climatic change. The pollen data indicate that the present pole forest vegetation at San Jorge began to assemble c. 200–150 cal yr BP. Given this young age, it is likely that the pole forest at this site remains in a state of transition

Vegetation history of Laysan Island, Northwestern Hawaiian Islands

Paleoenvironmental investigations were undertaken on Laysan Island in the remote Northwestern Hawaiian Islands to investigate its flora before historical observations. Substantial impacts occurred to the island as a result of late nineteenth- and early twentieth-century guano mining, commercial feather collecting, and denudation of vegetation by feral rabbits. An account of Laysan's historically known vegetation is presented, followed by discussion of results from the investigation of a 16.41-m sediment core froin Laysan's central hypersaline lake. The 7,000-year pollen and seed record, besides indicating the former importance of Pritchardia palms on Laysan, showed the former presence of Seven Previously unkown taxa, only four of which could be identified. Diatom analysis indicated fresh to brackish lake water during the early Holocene, a finding supported by the mollusk assemblage. Diatom diversity gradually decreased over time until there is a near monoculture, with types indicating a gradual increase of salinity. Hypersaline conditions were first recognizable near the top of the sequence with the appearance of Artemia zooplankton. Generally wetter Conditions Seem to have characterized the island before about 5,150 yr B.P., with drier conditions thereafter. The pollen record also suggests two possibly very brief periods of much drier conditions, conceivably related to El Nino-Southern Oscillation episodes

Local pollen analysis in a boreal forest setting : vegetation and land-use history at the summer farm Finnerudseter in south-eastern Norway

Traditional cultural landscapes are threatened in Europe due to changed land-use practices. However, the historical extent of this human land-use practice is not yet fully known. This thesis describes the vegetation history and human land-use at the summer farm Finnerudseter located in Nordmarka, the forested area north of Oslo. Historical documents states that the human land-use goes back to AD 1600 at this summer farm. However, extensive human landuse at Finnerudseter most likely predates AD 1600, and pollen and charcoal from a small forest hollow situated near Finnerudseter were analysed to reconstruct the local vegetation history at the site. The aims of the study was to document the general vegetation history, and to estimate in how long time and to what extent human land-use have taken place at Finnerudseter. The period investigated covered the vegetation history at the site from c. 2587 to 1334 cal. yr. BP (cal. yr., and all following dates are also presented as cal. yr.). Based on the results from the pollen count, the vegetation history was divided into 4 vegetation zones. Zone I Pinus period (c. 2587–2452 BP); Zone II Betula–Pinus–Alnus period (c. 2425–2237 BP); Zone III Betula–Pinus–Alnus–Picea period (c. 2183–1779 BP); Zone IV Picea–Betula period (c. 1630–1334 BP). Pinus was the dominant tree species from c. 2587–2452 BP. In addition, Picea established locally at the site during this period, c. 2479 BP. A local fire c. 2452 BP led to a shift in the tree species composition with a reduction in Pinus and increase in the pioneer trees Betula and Alnus. The finding of a single pollen from Cerealia may indicate small-scale cultivation c. 2425 BP. Small-scale livestock grazing seem to have been present from c. 2290 BP. Picea increased in amount c. 2183 BP, and the varying presence from c. 2183 to 1779 BP seem to be due to further forest clearing and human land-use. Picea became the dominant tree species c. 1630 BP, at the same time as human impact at Finnerudseter increased. The results clearly showed that human impact at Finnerudseter predated AD 1600 and probably started already in the Early Iron Age. However, there is gap from c. 1334 BP to 350 PB (AD 1600), which has not been investigated in this thesis, further research is therefore needed to get a more complete vegetation history at the summer farm Finnerudseter.M-ECO

Grazing activities and biodiversity history in the Pyrénées - new insights on high altitude ecosystems in the framework of a Human-Environment Observatory

International audienceReconstruction of the relationship between pastoral activities and vegetation history in the central Pyrenees demonstrates the importance of grazing pressure in the maintenance of floristic diversity in highland regions that have been abandone

The 4.2 ka event in the vegetation record of the central Mediterranean

In this paper, the variation in forest cover in the central Mediterranean region, reflected by percentage changes in the arboreal pollen record, has been examined in relation to the 4.2 ka event. A total of 36 well-dated and detailed pollen records from latitudes between 45 and 36 degrees N were selected and their vegetation dynamics between 5 and 3 ka examined in relation to the physiographic and climatic features of the study area and to the influence of human activity on past vegetation, as suggested by anthropogenic pollen indicators. We have found that the sites located between 43 and 45 degrees N do not show any significant vegetation change in correspondence with the 4.2 ka event. Several sites located on the Italian Peninsula between 39 and 43 degrees N show a marked opening of the forest, suggesting a vegetation response to the climate instability of the 4.2 ka event. Between 36 and 39 degrees N, a forest decline is always visible around 4.2 ka, and in some cases it is dramatic. This indicates that this region was severely affected by a climate change towards arid conditions that lasted a few hundred years and was followed by a recovery of forest vegetation in the Middle Bronze Age. Human activity, especially intense in southern Italy, may have been favored by this natural opening of vegetation. In Sardinia and Corsica, no clear change in vegetation is observed at the same time. We suggest that during the 4.2 ka event southern Italy and Tunisia were under the prevalent influence of a north African climate system characterized by a persistent high-pressure cell

The landscape and environment of Etruria

Etruria, homeland of the Etruscans, lies on the western coast of Italy to the north of Rome between the Tiber and the Arno rivers. This hilly region is defined by its low-lying coast and the rugged Apennine mountains to the north and east. Since the Etruscan period the sea level is little changed but there has been significant soil erosion modifying the hills and valleys. The climate in the Etruscan period was similar to today's but human action has modified the vegetation cover. To conclude, the major landscape zones of Etruria are briefly described

Pollenanalytical studies in NE-Nigeria: preliminary results from the Manga Grasslands and Lake Tilla, Biu Plateau

Two sites situated in the Sahelian and Sudanian zones of NE-Nigeria were chosen for pollen analysis. A sediment core from an interdunal depression in the eastern Manga Grassland provides information on the Holocene vegetation history of the Sahel between c. 9600-3400 B.P. The 3 m pollen record indicates an open savanna during the mid-Holocene. The presence of Sudano-Guinean taxa, which were mainly restricted to the interdunal depressions, points to more humid conditions. Already before c. 4000 B.P., a slow change towards drier conditions and the establishment of the modern Sahelian vegetation is visible in the diagram. This development was accompanied by high fire frequencies. A 16 m core from a crater lake (Lake Tilla) in the Sudanian zone of NE-Nigeria provides a pollen record which can be dated back to approximately 11-12000 B.P. Preliminary pollen spectra show a relatively constant pattern with a dominance of grass pollen even during the middle Holocene.Deux sites situés dans la zone sahélienne et soudanienne du NE-Nigeria ont été choisi pour l'analyse de pollen. L'analyse palynologique d'une carotte provenant d'une dépression interdunaire dans les Manga Grassland de l'Est a mis en évidence de nouvelles informations sur l'histoire de la végétation holocène du Sahel entre ca. 9600 et 3400 B.P. Le profile pollinique de 3 m montre l'existence d'une savane ouverte pendant l'holocène moyen. La présence d'éléments soudano-guinéens dont l'extension était surtout limitée à la dépression interdunaire indique des conditions plus humides. Dès avant ca. 4000 B.P., un lent changement des conditions vers une plus grande sècheresse et l'établissement d'une végétation sahélienne comparable à l'actuelle est visible sur le diagramme. Cette évolution fut accompagnée de fortes fréquences de feu. Une carotte de 16 m d'un lac cratére (Lake Tilla) dans la zone soudanienne du NE-Nigeria proviens une profile de 11-12000 ans environs. Le spèctra polliniques préliminaires sont relativement constante avec une dominance de graminées même pendant l'Holocene moyen

60,000 year climate and vegetation history of Southeast Alaska

Thesis (Ph.D.) University of Alaska Fairbanks, 2017Sedimentological and palynological analyses of lacustrine cores from Baker Island, located in Southeast Alaska's Alexander Archipelago, indicate that glaciers persisted on the island until ~14,500 cal yr. BP. However, the appearance of tree pollen, including Pinus cf. contorta ssp. contorta (shore pine) and Tsuga mertensiana (mountain hemlock) immediately following deglaciation suggests that a forest refugium may have been present on ice-free portions of neighboring islands or the adjacent continental shelf. Sedimentological and palynological analyses indicate a variable climate during the Younger Dryas interval between ~13,000 and ~11,500 cal yr. BP, with a cold and dry onset followed by ameliorating conditions during the latter half of the interval. An eight cm-thick black tephra dated to 13,500 ± 250 cal yr. BP is geochemically distinct from the Mt. Edgecumbe tephra and thus derived from a different volcano. Based on overall thickness, multiple normally graded beds, and grain size, I infer that the black tephra was emplaced by a large strombolian-style paroxysm. Because the dominant wind direction along this coast is from the west, the Addington Volcanic Field on the continental shelf, which would have been subaerially exposed during the eruption, is a potential source. The similarity in timing between this eruption and the Mt. Edgecumbe eruption suggests a shared trigger, possibly a response to unloading as the Cordilleran Ice Sheet retreated. To complement the Baker Island lacustrine record, a speleothem paleoclimate record based on δ¹³C and δ¹⁸O values spanning the interval from ~60,000 yr. BP to ~11,150 yr. BP was recovered from El Capitan Cave on neighboring Prince of Wales Island. More negative δ¹³C values are attributed to predominance of angiosperms in the vegetation above the cave at ~22,000 yr. BP and between ~53,000 and ~46,000 yr. BP while more positive δ¹³C values in speleothem EC-16-5-F indicate the presence of gymnosperms. These data suggest limited or no ice cover above El Capitan Cave for the duration of the record, possibly indicating that this region was a nunatak during glacial periods