scholarly journals Climate and vegetation changes during the Lateglacial and early–middle Holocene at Lake Ledro (southern Alps, Italy)

2013 ◽  
Vol 9 (2) ◽  
pp. 913-933 ◽  
Author(s):  
S. Joannin ◽  
B. Vannière ◽  
D. Galop ◽  
O. Peyron ◽  
J. N. Haas ◽  
...  
Keyword(s):  
Environmental Changes ◽  
Transition Period ◽  
Southern Alps ◽  
Dominant Factor ◽  
Vegetation Changes ◽  
Pollen Record ◽  
Lake Levels ◽  
Cold Event ◽  
Middle Holocene ◽  
Erosion Processes

Abstract. Adding to the on-going debate regarding vegetation recolonisation (more particularly the timing) in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081) from Lake Ledro (652 m a.s.l., southern Alps, Italy). Environmental changes were reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake levels, magnetic susceptibility and X-ray fluorescence (XRF) measurements) recorded climate and land-use changes during the Lateglacial and early–middle Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of tree species distribution. An altitude-dependent progressive time delay of the first continuous occurrence of Abies (fir) and of the Larix (larch) development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills) in northern Italy. Preboreal oscillations (ca. 11 000 cal BP), Boreal oscillations (ca. 10 200, 9300 cal BP) and the 8.2 kyr cold event suggest a centennial-scale climate forcing in the studied area. Picea (spruce) expansion occurred preferentially around 10 200 and 8200 cal BP in the south-eastern Alps, and therefore reflects the long-lasting cumulative effects of successive boreal and the 8.2 kyr cold event. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200–7300 cal BP evidenced in high lake levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal BP, a weak signal of pollen-based anthropogenic activities suggest weak human impact. The period between ca. 5700 and ca. 4100 cal BP is considered as a transition period to colder and wetter conditions (particularly during summers) that favoured a dense beech (Fagus) forest development which in return caused a distinctive yew (Taxus) decline. We conclude that climate was the dominant factor controlling vegetation changes and erosion processes during the early and middle Holocene (up to ca. 4100 cal BP).

scholarly journals Climate and vegetation changes during the Lateglacial and Early-Mid Holocene at Lake Ledro (southern Alps, Italy)

2012 ◽  
Vol 8 (6) ◽  
pp. 5583-5632 ◽  
Author(s):  
S. Joannin ◽  
B. Vannière ◽  
D. Galop ◽  
O. Peyron ◽  
J.-N. Haas ◽  
...  
Keyword(s):  
Environmental Changes ◽  
Transition Period ◽  
Anthropogenic Activities ◽  
Southern Alps ◽  
Dominant Factor ◽  
Vegetation Changes ◽  
Pollen Record ◽  
Lake Levels ◽  
Cold Event ◽  
Erosion Processes

Abstract. Adding to the on-going debate regarding vegetation recolonisation in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081) from Lake Ledro (652 m a.s.l., southern Alps, Italy). Environmental changes that where reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake-levels, magnetic susceptibility and X-ray fluorescence (XRF) measurements) recorded climate and land-use changes during the Lateglacial and Early-Mid Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of distribution tree species. An altitude-dependent progressive time-delay of the first continuous occurrence of Abies (fir) and of the Larix (larch) development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills) in northern Italy. Preboreal oscillations (ca. 11 000 cal. BP), Boreal oscillations (ca. 10 200, 9300 cal. BP) and n.e. 8.2 kyr cold event suggest a centennial-scale short-lasting climate forcing in the studied area. Picea (spruce) expansion occurred preferentially around 10 200 cal. BP and 8200 cal. BP in the south-eastern Alps and, therefore, reflects the long-lasting cumulative effects of successive boreal and 8.2 kyr cold events. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200–7300 cal. BP evidenced in high lake-levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal. BP, low signal of pollen-based anthropogenic activities suggest a weak human impact. The period between ca. 5700 and ca. 4100 cal. BP is considered as a transition period to colder and wetter conditions (particularly during summers) that favoured a dense beech (Fagus) forest development which in return caused a distinctive yew (Taxus) decline. We conclude that climate was the dominant factor controlling vegetation changes and erosion processes during the Early and Mid Holocene (up to ca. 4100 cal. BP).

Vegetation changes and sediment transfers in the catchment of Lake Alaotra, Madagascar

2021 ◽  
Author(s):  
Nils Broothaerts ◽  
Vao Fenotiana Razanamahandry ◽  
Liesa Brosens ◽  
Benjamin Campforts ◽  
Liesbet Jacobs ◽  
...  
Keyword(s):  
Human Disturbance ◽  
Environmental Changes ◽  
Vegetation Changes ◽  
Pollen Record ◽  
Radiocarbon Dates ◽  
Sediment Fluxes ◽  
Erosion Rates ◽  
Erosion Processes ◽  
Sediment Mobilization

<p>To understand the driving processes for changes in African ecosystems and related problems such as soil degradation, it is crucial to gain insight in the relative importance of human disturbance and climate change. Madagascar is known for its particularly high erosion rates in the central highlands, yet the role of human disturbance versus natural processes are not well understood and is a topic of ongoing debate. Recent studies have challenged the traditional view that the currently observed intense erosion processes and sediment fluxes in Madagascar are mainly driven by recent large-scale deforestation. However, at present almost no quantitative data is available to couple vegetation dynamics and sediment fluxes over time in Madagascar. This study aims to provide more insight in landscape changes (vegetation changes, sediment mobilization and deposition) in central Madagascar, and in the specific role of man and climate. The study focuses on the 1800 km² catchment of Lake Alaotra, located ca 200 km northeast of Antananarivo. Lake Alaotra is formed in a graben system in the highlands of Madagascar, and is the largest freshwater lake of the country (400 km²). A pollen record from the lake was used to reconstruct regional vegetation changes. Radiocarbon dates of extracted pollen provide a detailed chronostratigraphic framework. Augerings and radiocarbon dates from floodplains and marshes in the catchment were used to reconstruct the sediment deposition history. The pollen record and charcoal data shows the vegetation changes over the last 3000 years. The main observed shift in vegetation is a transition from a woodland/grassland mosaic towards an open grassland, starting ca 1850 years ago, which coincides with the onset of human activities. Data on floodplain sedimentation show an increase in accumulation rates in the last 600 years, from ca 1 mm yr<sup>-1</sup> to ca 30 mm yr<sup>-1</sup>, which can be linked to increased hillslope erosion rates during that time period. The sedimentation wave, however, does not reach Lake Alaotra nor the surrounding marshes as floodplains act as a buffer. Overall, this study provides a spatial and temporal integrated reconstruction of vegetation changes in the Lake Alaotra catchment and the link with sediment mobilization and deposition, thereby providing a better understanding of environmental changes in central Madagascar and its driving forces.</p>

scholarly journals Millennial-scale climatic variability between 340 000 and 270 000 years ago in SW Europe: evidence from a NW Iberian margin pollen sequence

2009 ◽  
Vol 5 (1) ◽  
pp. 53-72 ◽  
Author(s):  
S. Desprat ◽  
M. F. Sánchez Goñi ◽  
J. F. McManus ◽  
J. Duprat ◽  
E. Cortijo
Keyword(s):  
Climatic Variability ◽  
Interglacial Period ◽  
Vegetation Changes ◽  
Pollen Record ◽  
Cold Event ◽  
Ice Volume ◽  
The North ◽  
Nw Iberia ◽  
Iberian Margin ◽  
Millennial Scale

Abstract. We present a new high-resolution marine pollen record from NW Iberian margin sediments (core MD03-2697) covering the interval between 340 000 and 270 000 years ago, a time period centred on Marine Isotope Stage (MIS) 9 and characterized by particular baseline climate states. This study enables the documentation of vegetation changes in the north-western Iberian Peninsula and therefore the terrestrial climatic variability at orbital and in particular at millennial scales during MIS 9, directly on a marine stratigraphy. Suborbital vegetation changes in NW Iberia in response to cool/cold events are detected throughout the studied interval even during MIS 9e ice volume minimum. However, they appear more frequent and of higher amplitude during the 30 000 years following the MIS 9e interglacial period and during the MIS 9a-8 transition, which correspond to intervals of an intermediate to high ice volume and mainly periods of ice growth. Each suborbital cold event detected in NW Iberia has a counterpart in the Southern Iberian margin SST record. High to moderate amplitude cold episodes detected on land and in the ocean appear to be related to changes in deep water circulation and probably to iceberg discharges at least during MIS 9d, the mid-MIS 9c cold event and MIS 9b. This work provides therefore additional evidence of pervasive millennial-scale climatic variability in the North Atlantic borderlands throughout past climatic cycles of the Late Pleistocene, regardless of glacial state. However, ice volume might have an indirect influence on the amplitude of the millennial climatic changes in Southern Europe.

Radiocarbon-Dated Pollen and Sediment Records From Near the Boylston Street Fishweir Site in Boston, Massachusetts

1994 ◽  
Vol 41 (2) ◽  
pp. 214-224 ◽  
Author(s):  
Paige E. Newby ◽  
Thompson Webb
Keyword(s):  
New England ◽  
Tidal Flow ◽  
Vegetation Changes ◽  
Pollen Record ◽  
Marine Animals ◽  
Middle Holocene ◽  
Archaeological Data ◽  
Bay Area ◽  
Southern New England ◽  
Water Vegetation

AbstractA radiocarbon-dated pollen record near the Boylston Street Fishweir site in Boston; Massachusetts, provides a regional and local record of vegetation changes from the middle Holocene to present. The stratigraphy begins about 5630 ± 90 yr B.P. with a marine transgression and is continuous up to the historic backfilling of the Back Bay area about 100 yr B.P. When pollen began accumulating at the site, the immediate area resembled the swamp forests growing today in southern New England. Fresh- and brackish-water vegetation was present before the area near the site was submerged. While these vegetation changes occurred locally, oak forest grew in the region. Correlation of this stratigraphy with archaeological data collected from 500 Boylston Street indicates that between 4700 and 3700 yr B.P., a number of fence-like alignments ("weirs"), were probably placed within existing channels and/or along shorelines to capture fish and other marine animals as they moved with the tidal flow.

scholarly journals Human Activity Influences on Vegetation Cover Changes in Beijing, China, from 2000 to 2015

2017 ◽  
Vol 9 (3) ◽  
pp. 271 ◽  
Author(s):  
Meichen Jiang ◽  
Shufang Tian ◽  
Zhaoju Zheng ◽  
Qian Zhan ◽  
Yuexin He
Keyword(s):  
Correlation Analysis ◽  
Human Activity ◽  
Environmental Changes ◽  
Rapid Development ◽  
Central City ◽  
Source Control ◽  
Vegetation Coverage ◽  
Dominant Factor ◽  
Vegetation Changes ◽  
Human Society

For centuries, the rapid development of human society has already made human activity the dominant factor in the terrestrial ecosystem. As the city of greatest importance in China, the capital Beijing has experienced eco-environmental changes with unprecedented economic and population growth during the past few decades. To better understand the ecological transition and its correlations in Beijing, Landsat Thematic Mapper (TM) and Operational Land Imager (OLI) images were used to investigate vegetation coverage changes using a dimidiate pixel model. Piecewise linear regression, bivariate-partial correlation analysis, and factor analysis were applied to the probing of the relationship between vegetation coverage changes and climatic/human-induced factors. The results showed that from 2000 to 2005, 2005 to 2010, and 2010 to 2015, Beijing experienced both restoration (6.33%, 10.08%, and 12.81%, respectively) and degradation (13.62%, 9.35%, and 9.49%, respectively). The correlation analysis results between climate and vegetation changes demonstrated that from 2000 to 2015, both the multi-year annual mean temperature (r = −0.819, p < 0.01) and the multi-year annual mean precipitation (r = 0.653, p < 0.05) had a significantly correlated relationship with vegetation change. The Beijing-Tianjin Sandstorm Source Control Project (BTSSCP) has shown beneficial spatial effects on vegetation restoration; the total effectiveness in conservation areas (84.94 in 2000–2010) was much better than non-BTSSCP areas (34.34 in 2000–2010). The most contributory socioeconomic factors were the population (contribution = 54.356%) and gross domestic product (GDP) (contribution = 30.677%). The population showed a significantly negative correlation with the overall vegetation coverage (r = −0.684, p < 0.05). The GDP was significantly negatively correlated with vegetation in Tongzhou, Daxing, Central city, Fangshan, Shunyi, and Changping (r = −0.601, p < 0.01), while positively related in Huairou, Miyun, Pinggu, Mentougou and Yanqing (r = 0.614, p < 0.01). These findings confirm that human activity is a very significant factor in impacting and explaining vegetation changes, and that some socioeconomic influences on vegetation coverage are highly spatially heterogeneous, based on the context of different areas.

scholarly journals Millennial-scale climatic variability between 340 000 and 270 000 years ago in SW Europe: evidence from a NW Iberian margin pollen sequence

2008 ◽  
Vol 4 (2) ◽  
pp. 375-414 ◽  
Author(s):  
S. Desprat ◽  
M. F. Sánchez Goñi ◽  
J. Duprat ◽  
E. Cortijo ◽  
J. F. McManus
Keyword(s):  
Climatic Variability ◽  
Interglacial Period ◽  
Vegetation Changes ◽  
Pollen Record ◽  
Cold Event ◽  
Ice Volume ◽  
The North ◽  
Nw Iberia ◽  
Iberian Margin ◽  
Millennial Scale

Abstract. We present a new high-resolution marine pollen record from NW Iberian margin sediments (core MD03-2697) covering the interval between 340 000 and 270 000 years ago a time period centred on Marine Isotope Stage (MIS) 9 and characterised by particular baseline climate states. This study enables to document the vegetation changes in north-western Iberian Peninsula and therefore the terrestrial climatic variability at orbital and in particular at millennial scales during MIS 9, directly on a marine stratigraphy. Suborbital vegetation changes in NW Iberia in response to cool/cold events are detected throughout the studied interval even during MIS 9e ice volume minimum. However, they appears more frequent and of higher amplitude during the 30 000 years following the MIS 9e interglacial period and during the MIS 9a-8 transition which correspond to intervals of an intermediate to high ice volume and mainly periods of ice growth. Each suborbital cold event detected in NW Iberia has a counterpart in the southern Iberian margin SST record. High to moderate amplitude cold episodes detected on land and in the ocean appears related to changes in deep water circulation and likely to iceberg discharges at least during MIS 9d, the mid-MIS 9c cold event and MIS 9b. This work provides therefore additional evidence of a pervasive millennial-scale climatic variability in the North Atlantic borderlands throughout past climatic cycles of the Late Pleistocene, regardless of glacial state. However, ice volume might have an indirect influence on the amplitude of the millennial climatic changes in southern Europe.

Holocene diatom assemblages from Dunderbukhta sediments, West Svalbard

2019 ◽  
pp. 242-245
Author(s):  
Ksenya V. Poleshchuk ◽  
Zinaida V. Pushina ◽  
Sergey R. Verkulich
Keyword(s):  
Environmental Changes ◽  
Ecological Groups ◽  
Diatom Assemblages ◽  
Diatom Analysis ◽  
Diatom Flora ◽  
Sediment Samples ◽  
Ecological Zones ◽  
Middle Holocene ◽  
Temperature Trends

The diatom analysis results of sediment samples from Dunderbukta area (Wedel Jarlsberg Land, West Svalbard) are presented in this paper. The diatom flora consists of four ecological groups, which ratio indicates three ecological zones. These zones show environmental changes of the area in early–middle Holocene that is demonstrating periods of regression and temperature trends.

Species distribution modeling reveals the ecological niche of extinct megafauna from South America

2021 ◽  
pp. 1-8
Author(s):  
Thaísa Araújo ◽  
Helena Machado ◽  
Dimila Mothé ◽  
Leonardo dos Santos Avilla
Keyword(s):  
South America ◽  
Species Distribution ◽  
Environmental Changes ◽  
Species Distribution Modeling ◽  
Human Action ◽  
Northeastern Brazil ◽  
Climate Conditions ◽  
Middle Holocene ◽  
Distribution Modeling ◽  
The Impact

Abstract Climatic and environmental changes, as well as human action, have been cited as potential causes for the extinction of megafauna in South America at the end of the Pleistocene. Among megamammals lineages with Holarctic origin, only horses and proboscideans went extinct in South America during this period. This study aims to understand how the spatial extent of habitats suitable for Equus neogeus and Notiomastodon platensis changed between the last glacial maximum (LGM) and the middle Holocene in order to determine the impact that climatic and environmental changes had on these taxa. We used species distribution modeling to estimate their potential extent on the continent and found that both species occupied arid and semiarid open lands during the LGM, mainly in the Pampean region of Argentina, southern and northeastern Brazil, and parts of the Andes. However, when climate conditions changed from dry and cold during the LGM to humid and warm during the middle Holocene, the areas suitable for these taxa were reduced dramatically. These results support the hypothesis that climatic changes were a driving cause of extinction of these megamammals in South America, although we cannot rule out the impact of human actions or other potential causes for their extinction.

Late Pleistocene and Holocene Paleoenvironments of Chalco Lake, Central Mexico

1993 ◽  
Vol 40 (3) ◽  
pp. 332-342 ◽  
Author(s):  
Maria Socorro Lozano-Garcı́a ◽  
Beatriz Ortega-Guerrero ◽  
Margarita Caballero-Miranda ◽  
Jaime Urrutia-Fucugauchi
Keyword(s):  
Volcanic Activity ◽  
Lake Level ◽  
Environmental Changes ◽  
Late Quaternary ◽  
Cold Climate ◽  
Central Mexico ◽  
Pollen Record ◽  
Loss On Ignition ◽  
Southeastern Part ◽  
Saline Marsh

AbstractIn order to establish paleoenvironmental conditions during the late Quaternary, four cores from the Basin of Mexico (central Mexico) were drilled in Chalco Lake, located in the southeastern part of the basin. The upper 8 m of two parallel cores were studied, using paleomagnetic, loss-on-ignition, pollen, and diatom analyses. Based on 11 14C ages, the analyzed record spans the last 19,000 14C yr B.P. Volcanic activity has affected microfossil abundances, both directly and indirectly, resulting in absence or reduction of pollen and diatom assemblages. Important volcanic activity took place between 19,000 and 15,000 yr B.P. when the lake was a shallow alkaline marsh and an increase of grassland pollen suggests a dry, cold climate. During this interval, abrupt environmental changes with increasing moisture occurred. From 15,000 until 12,500 yr B.P. the lake level increased and the pollen indicates wetter conditions. The highest lake level is registered from 12,500 to ca. 9000 yr B.P. The end of the Pleistocene is characterized by an increase in humidity. From 9000 until ca. 3000 yr B.P. Chalco Lake was a saline marsh and the pollen record indicates warmer conditions. After 3000 yr B.P. the lake level increased and human disturbance dominates the lacustrine record.

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