16 research outputs found
14,000 years of climatic and anthropogenic change in the Afromontane forest of São Tomé Island, Gulf of Guinea
São Tomé (Gulf of Guinea, Central Africa) is a 854 km2 tropical island that had a pivotal role in early European colonial expansion through the Atlantic between the 15th and 16th centuries. Historical sources suggest that native vegetation has been heavily impacted since human arrival (1470 CE) due to monoculture economies and the introduction of mammals and plants, some of which now have established wild populations. The Afromontane forest of São Tomé, located above 800 m.a.sl., is particularly rich in endemic plant species and has remained relatively unaffected by direct human impacts. Here, we explore how environmental change influenced this forest through the study of a sedimentary sequence from the volcanic crater of Lagoa Amélia (1340 m a.s.l.), a palustrine system located at the boundary between submontane (800–1400 m a.s.l.) and mist forest (above 1400 m a.s.l.). We used fossil pollen, non-pollen palynomorphs, sedimentology and charcoal to determine forest dynamics from the Late Pleistocene to the present. From 14,000 to 12,500 cal yr BP the forest was dominated by taxa from higher altitudes, adapted to cooler and drier climates (e.g. Afrocarpus mannii trees and Psychotria nubicola). After 12,500 cal yr BP, a potential uphill migration was identified by an increase in taxa like the trees Symphonia globulifera and Craterispermum cerinanthum. From 11,200 cal yr BP through the rest of the Holocene taxa from lower altitudes became dominant (e.g. Prunus africana, Polyscias, and Sabicea), except at c. 8500 cal yr BP when rapid cooling led to forest opening. Charcoal showed that fires were frequent during the Late Pleistocene (14,000 to 11,200 cal yr BP), becoming rare during the Holocene until anthropogenic fires started at c. 220 cal yr BP. Other recent anthropogenic impacts detected in Lagoa Amélia included the appearance of pollen of introduced plant species (e.g., Cestrum), and the increase in pollen of economically important species (Elaeis guineensis, Zea mays) and in fungal spores related to introduced herbivores. Our results reveal that climate changed the altitudinal distribution of the Afromontane forest in São Tomé during the Late Pleistocene, as observed on the African continent, and that this ecosystem was also strongly impacted by human arrival, through fire, farming, and introduced species.info:eu-repo/semantics/publishedVersio
Pollen data: Influences of sea level changes and volcanic eruptions on Holocene vegetation in Tonga
<p><strong>Aim</strong>:</p>
<p>To investigate mid- to late-Holocene vegetation changes on low-lying coastal areas in Tonga and how changing sea level and recurrent volcanic eruptions have influenced vegetation dynamics on four islands of the Tongan Archipelago (South Pacific).</p>
<p><strong>Methods: </strong></p>
<p>To investigate past vegetation and environmental change at Ngofe Marsh ('Uta Vava'u) we examined palynomorphs (pollen and spores), charcoal (fire), and sediment characteristics (volcanic activity) from a 6.7-m long sediment core. Radiocarbon dating indicated the sediments were deposited over the last 7700 years. We integrated the Ngofe Marsh data with similar previously published data from Avai'o'vuna Swamp on Pangaimotu Island, Lotofoa Swamp on Foa Island, and Finemui Swamp on Ha'afeva Island. Plant taxa were categorised as littoral, mangrove, rainforest, successional/ disturbance, and wetland groups and linear models were used to examine relationships between vegetation, relative sea-level change, and volcanic eruptions (tephra).</p>
<p><strong>Results</strong>:</p>
<p>Relative sea-level change has impacted vegetation on three of the four islands investigated. Volcanic eruptions were not identified as a driver of vegetation change. Rainforest decline does not appear to be driven by sea-level changes or volcanic eruptions. From all sites analysed, vegetation at Finemui Swamp was most sensitive to changes in relative sea level.</p>
<p><strong>Conclusions: </strong></p>
<p>While vegetation on low-lying Pacific islands is sensitive to changing sea levels, island characteristics, such as size and elevation, are also likely to be important factors that mediate specific island responses to drivers of change.</p><p>Funding provided by: Natural Environment Research Council<br>Crossref Funder Registry ID: https://ror.org/02b5d8509<br>Award Number: NE/L002531/1</p>
The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC
Lina Mire, Gotland, is an area of archaeological significance and has a complex history of shoreline displacement. Archaeologists suspect that Lina Mire was once part of an important inland water system which connected the Littorina Sea with central Gotland. This study investigates vegetational and palaeoenvironmental changes of the Lina Mire area between 6900 – 400 BC (8850 – 2350 cal years BP) in order to better understand how the area has developed and how humans have impacted the vegetation. Pollen analysis, C/N ratios, organic matter and carbon content measurements were conducted. The chronology was based on 14C AMS dating of terrestrial macrofossils and bulk sediments. A transgression of the Littorina Sea at about 6550 BC (8500 cal years BP) inundated the Lina Mire basin, which was a lake at the time. The onset of cultivation was indicated by the presence of Hordeum (Barley or Wild Barley) during the Late Neolithic, 2630 BC (4580 cal years BP). Hordeum continued to grow during the Bronze Age when Cereals appeared at about 970 BC (2920 cal years BP). During the onset of cultivation during the Late Neolithic, the Lina Mire basin was a bay of the Littorina Sea. The Lina Mire basin remained connected with the Littorina Sea until isostatic uplift caused it to become isolated at about 1870 BC (3820 cal years BP). The lake overgrew and became a mire about 820 BC (2770 cal years BP)
Palaeoecological responses to environmental changes on South Pacific islands.
South Pacific island ecosystems are exposed to numerous disturbances, which are both abiotic and human-driven in nature. However, little is known about the long-term responses (>100 year) of these ecosystems to such events. Palaeoecological methods can provide information about responses, recovery times, and extend our knowledge of vegetation change beyond recent history through centuries and millennia. Focusing on the South Pacific islands this thesis aims to understand how periods of environmental disturbance such as climate variability, fire regime change, human arrival, relative sea level change, and volcanic eruptions have altered ecosystems. Specifically, three of the thesis aims are to understand 1) how local vegetation responded to volcanic eruptions and sea-level change during the Mid-Late Holocene in the Tongan archipelago. 2) To quantify at high resolution (~5 years) how the forests surrounding Lake Emaotul, Efate, Vanuatu, and the lake ecosystem responded to the 1450s CE Kuwae eruption and a shift towards drier climate conditions ~1100 cal. years BP. 3) A regional analysis of 15 sites on 13 islands, where the aim is to analyse regional patterns of biotic similarity throughout the past 5000 years. Methods used to investigate the aims of the thesis are biomarker analysis, charcoal, chironomids, fossil pollen and spore analysis, magnetic susceptibility, radiocarbon dating, tephra analysis, and XRF. Additionally, statistical techniques such as Bray-Curtis similarity, cluster analysis, ordination, and regression models were used. Data from published pollen records was also incorporated. Results show that in Tonga, relative sea level was a more important driver of change for local vegetation than volcanic eruptions. In addition, smaller, low-elevation island littoral, mangrove, successional, and wetland vegetation may be more vulnerable to sea level changes than vegetation on larger or higher elevation islands or inland vegetation habitats such as rainforest. Analyses from Lake Emaotul, Vanuatu, shows that vegetation turnover increased following the 1450s CE Kuwae eruption. Vegetation and chironomid turnover also increased following a shift towards drier climate conditions ~1100 cal. years BP. The Lake Emaotul analyses also reveal that a recent increase in burning regime led to an increase in vegetation turnover during the last ~85 years. Biotic similarity analyses across South Pacific islands revealed a 5000 year long trend of biotic homogenisation which accelerated ~3150 cal. years BP synchronous with human arrival to many Southwestern Pacific islands.Four major conclusions can be determined from this work; 1) volcanic eruptions alter vegetation communities in some instances and this can be captured with high-resolution pollen sampling strategies (e.g., the Lake Emaotul record); 2) coastal vegetation communities on low-elevation and/or small islands may be more at risk from sea level rise; 3) vegetation and chironomid communities are sensitive to decreases in precipitation, and 4) human presence on South Pacific islands may have led to enhanced biotic homogenisation. These analyses extend our knowledge of ecological change on South Pacific islands and highlight the importance of environmental disturbances as drivers of ecosystem change
Dataset supporting the University of Southampton Doctoral Thesis "Palaeoecological responses to environmental changes on South Pacific islands".
This dataset is supporting the University of Southampton Doctoral Thesis "Palaeoecological responses to environmental changes on South Pacific islands".
The files are in CSV format and the R code should be accessed using RStudio software and contain:
Feacal_biomarker_data.xlsx
Biotic_homogenisation_main.zip
Vanuatu_main.zip
Tonga_main.zip
This work was funded by the NERC PhD stipend NE/L002531/1
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Taming Fogo Island: Late-Holocene volcanism, natural fires and land use as recorded in a scoria-cone sediment sequence in Cabo Verde
Cabo Verde remained uninhabited until 1460 CE, when European sailors founded a settlement in Santiago, and soon after in Fogo island. The degree to which different island ecosystems in Cabo Verde have been transformed by humans remains uncertain because of a scarcity of historical information and archaeological evidence. Disentangling these processes from natural ones is complicated in islands with a history of volcanic impacts and other natural hazards. In this paper, we apply microfossil (pollen, non-pollen palynomorphs and phytoliths) and sedimentological analyses (granulometry, X-ray diffraction, loss on ignition and tephrostratigraphy) to a 2-m sediment sequence deposited in a scoria cone from 4100 cal year BP (calibrated years before 1950 CE) to the present. The organic-rich basal sediments indicate that between 4100 and 2600 cal year BP the pre-settlement landscape of Fogo was an open grassland, where fire was infrequent and/or small-scale. An increase in volcanic glass deposition after 2600 cal year BP, peaking ca. 1200 cal year BP, suggests that there was a progressive activation of Fogo’s volcanic activity, contemporaneous with increased fire frequency and erosion pulses, but with little impact on local grassland vegetation. While dating uncertainty is high, the first evidence of intensive local land use by early settlers was in the form of cultivation of Zea mays, abundant spores of coprophilous fungi (i.e. Sporormiella), and peaks in charcoal concentrations between 800 and 400 cal year BP. This was followed by large increases in pollen from pigeon pea (Cajanus), a diverse array of exotic trees (Cupressus, Grevillea), and invasive shrubs (Lantana). The introduction of these taxa is part of recent human effort to ‘tame’ this steep, dry and hazardous island by reducing erosion and providing firewood. An important outcome of these efforts, however, is a loss of fragile native biodiversity.</p
Mid-late Holocene vegetation history of the Argive Plain (Peloponnese, Greece) as inferred from a pollen record from ancient Lake Lerna
This study provides a high-resolution reconstruction of the vegetation of the Argive Plain (Peloponnese, Greece) covering 5000 years from the Early Bronze Age onwards. The well dated pollen record from ancient Lake Lerna has been interpreted in the light of archaeological and historical sources, climatic data from the same core and other regional proxies. Our results demonstrate a significant degree of human impact on the environments of the Argive Plain throughout the study period. During the Early Bronze Age evidence of a thermophilous vegetation is seen in the pollen record, representing the mixed deciduous oak woodland of the Peloponnesian uplands. The plain was mainly used for the cultivation of cereals, whereas local fen conditions prevailed at the coring site. Towards the end of this period an increasing water table is recorded and the fen turns into a lake, despite more arid conditions. In the Late Bronze Age, the presence of important palatial centres modified the landscape resulting in decrease of mixed deciduous oak woodland and increase in open land, partly used for grazing. Possibly, the human management produced a permanent hydrological change at Lake Lerna. From the Archaic period onwards the increasing human pressure in association with local drier conditions caused landscape instability, as attested by a dramatic alluvial event recorded in the Pinus curve at the end of the Hellenistic Age. Wet conditions coincided with Roman times and favoured a forest regeneration pattern in the area, at the same time as we see the most intensive olive cultivation in the pollen record. The establishment of an economic landscape primarily based on pastures is recorded in the Byzantine period and continues until modern times. Overgrazing and fires in combination with arid conditions likely caused degradation of the vegetation into garrigue, as seen in the area of the Argive Plain today.</p
Influences of sea level changes and volcanic eruptions on Holocene vegetation in Tonga
Here, we investigate Mid- to Late-Holocene vegetation changes in low-lying coastal areas in Tonga and how changing sea levels and recurrent volcanic eruptions have influenced vegetation dynamics on four islands of the Tongan archipelago (South Pacific). To investigate past vegetation and environmental change at Ngofe Marsh (‘Uta Vava’u), we examined palynomorphs (pollen and spores), charcoal (fire), and sediment characteristics (volcanic activity) from a 6.7-m-long sediment core. Radiocarbon dating indicated the sediments were deposited over the last 7700 years. We integrated the Ngofe Marsh data with similar previously published data from Avai’o’vuna Swamp on Pangaimotu Island, Lotofoa Swamp on Foa Island, and Finemui Swamp on Ha’afeva Island. Plant taxa were categorized as littoral, mangrove, rainforest, successional/ disturbance, and wetland groups, and linear models were used to examine relationships between vegetation, relative sea level change, and volcanic eruptions (tephra). We found that relative sea level change has impacted vegetation on three of the four islands investigated. Volcanic eruptions were not identified as a driver of vegetation change. Rainforest decline does not appear to be driven by sea level changes or volcanic eruptions. From all sites analyzed, vegetation at Finemui Swamp was most sensitive to changes in relative sea level. While vegetation on low-lying Pacific islands is sensitive to changing sea levels, island characteristics, such as area and elevation, are also likely to be important factors that mediate specific island responses to drivers of change
Island ecosystem responses to the Kuwae eruption and precipitation change over the last 1600 years, Efate, Vanuatu
Introduction: islands of the Southwest Pacific are exposed to geologic and climate-related disturbances that occur on a range of timescales and which probably affect, to varying degrees, their terrestrial ecosystems. Over the past ∼1100 years we know of two major events in the region: the Kuwae eruption which is thought to have occurred ∼500 cal. years BP and a shift to drier conditions which began ∼1100 cal. years BP. Methods: we investigated terrestrial and lacustrine ecosystem responses to these events and also to a changing fire regime, likely human-caused, using a multi-proxy (C/N, charcoal, chironomids, pollen, and tephra) record from Lake Emaotul, Efate, Vanuatu. Results: Tephra from the Kuwae eruption was found across a 6 cm layer which our age-depth model suggests was deposited 650–510 cal. years BP (95% confidence). Forest and chironomid community turnover increased during the wet-dry shift 1100–1000 cal. years BP; subsequently, chironomid turnover rates decreased again within <135 years and vegetation had partially (but not fully) recovered after ∼80 years. Following Kuwae volcanic tephra deposition, vegetation turnover increased again, reflecting a reduction in small trees and shrubs and an increase in grasses. Subsequently, the forest vegetation did not regain its previous composition, whereas chironomid community composition remained fairly stable before and after tephra deposition. Within the last ∼90 years, enhanced local burning drove another increase in vegetation turnover. Discussion: terrestrial and freshwater ecosystems in Efate are sensitive to changes in hydroclimate, volcanism, and anthropogenic fires, although to different degrees; while recent human impacts are often obvious, volcanic eruptions and climatic shifts have also structured Pacific-island ecosystems and will continue to do so.</p