Three Millennia of Vegetation, Land-Use and Climate Change in SE Sicily

This study presents the first Late Holocene marine pollen record (core ND2) from SE Sicily. It encompasses the last 3000 years and is one of the most detailed records of the south-central Mediterranean region in terms of time resolution. The combined approach of marine palynology and historical ecology, supported by independent palaeoclimate proxies, provides an integrated regional reconstruction of past vegetational dynamics in relation to rapid climatic fluctuations, historical socio-economic processes, and past land-use practices, offering new insights into the vegetation history of SE Sicily. Short-term variations of sparse tree cover in persistently open landscapes reflect rapid hydroclimatic changes and historical land-use practices. Four main phases of forest reduction are found in relation to the 2.8 ka BP event, including the Late Antique Little Ice Age, the Medieval Climate Anomaly, and the Little Ice Age, respectively. Forest recovery is recorded during the Hellenistic and Roman Republican Periods, the Early Middle Ages, and the last century. Agricultural and silvicultural practices, as well as stock-breeding activities, had a primary role in shaping the current vegetational landscape of SE Sicily.

Expression of the “4.2 ka event” drought in the southern Rocky Mountains, USA

The use of the climatic anomaly known as the “4.2 ka event” as the stratigraphic division between the mid- and late Holocene has prompted debate over its impact, geographic pattern, and significance. The anomaly has primarily been described as abrupt drying, but evidence of hydroclimate change at ca. 4 ka is inconsistent among sites globally, and few sites in North America document a major drought. Climate records from the southern Rocky Mountains demonstrate the challenge with diagnosing the extent and severity of the anomaly. Dune-field chronologies and a pollen record in southeast Wyoming reveal several centuries of low moisture at around 4.2 ka and prominent low stands in lakes in Colorado suggest the drought was unique amid Holocene variability, but detailed carbonate oxygen isotope (δ18Ocarb) records from Colorado do not record it. We find new evidence from δ18Ocarb in a small mountain lake in southeast Wyoming of an abrupt reduction in effective moisture or snowpack from approximately 4.2–4 ka that coincides in time with the other evidence from the southern Rocky Mountains and the western Great Plains of regional drying at around 4.2 ka. We find that the δ18Ocarb in our record may reflect cool-season inputs into the lake, which do not appear to track the strong enrichment of heavy oxygen by evaporation during summer months today. The modern relationship differs from some widely applied conceptual models of lake-isotope systems and may indicate reduced winter precipitation rather than enhanced evaporation at ca. 4.2 ka. Inconsistencies among the North American records, particularly in δ18Ocarb trends, thus show that site-specific factors can prevent identification of the patterns of multi-century drought. However, the prominence of the drought at ca. 4 ka among a growing number of sites in the North American interior suggests it was a regionally substantial climate event amid other Holocene variability.

Two-phased Mass Rarity and Extinction in Land Plants During the End-Triassic Climate Crisis

Greenhouse gas emissions from large-scale volcanism in the Central Atlantic Magmatic Province is considered to have caused the end-Triassic mass extinction (201.5 million years ago), but the impact on land plants has been debated. Here, abundance changes in spores and pollen record the devastating effects this volcanic induced climate crisis had on coastal and near-coastal lowland mire vegetation around the European epicontinental sea and the European Tethys margin. Combined stress from rising air temperatures and changing climate at the onset of the crisis was exacerbated by a rapidly rising sea-level resulting in fragmentation and destruction of coastal and near-coastal lowland mire habitats, causing mass rarity and extinctions primarily in gymnosperm trees and shrubs adapted to these environments. The devastation of these habitats was further amplified by a subsequent sea-level fall leaving pioneering opportunists and herbaceous survivors to colonize disturbed areas in an environment stressed by increased wildfire activity and enhanced soil erosion. The pioneering flora was severely decimated in a second mass rarity phase and ultimately extirpated. The second mass rarity phase occurred just prior to and at the onset of a prominent negative excursion in δ13Corg. A subsequent sea-level rise appears to have restored some of the near-coastal mire habitats allowing some of plants to recover. The supraregional mass rarity during the end-Triassic crisis affected both previously dominant as well as rare plants and this resonates with ongoing and future climate change and attests to the vulnerability of coastal and lowland vegetation, especially rare plant species, to climatic and environmental disturbances, where rising sea-level threatens entire ecosystems.

Investigations of plant subfossil cuticles at a Holocene raised bog complex, northern New Zealand

<p>Subfossil plant cuticles, the very resistant waxy layer covering vascular land plants, are a neglected source of information in peat studies, despite their high preservation and identification potential. A lack of standardised methods and reference material are major contributing factors. In this thesis, a new method is introduced to test if subfossil plant cuticles from Moanatuatua Bog in the northern North Island of New Zealand can give a robust reconstruction of local bog surface vegetation changes during the Holocene. The method was successfully established and applied at coarse sampling resolution to show vegetation changes across the full length of the core and at fine sampling resolution around charcoal layers to reconstruct the post-fire response pattern of the main plant species on the bog. Additionally, bulk density and organic matter analyses were carried out to provide further insight into these changes. At the core site, towards the southern margins of Moanatuatua Bog, swamp forest had developed by 15000 cal yr BP. Until ca. 10500 cal yr BP, the vegetation assemblage was sedge-dominated, indicating swamp and/or fen conditions. A significant increase in macroscopic charcoal particles coincided with the transition to a more diversified vegetation composition. At around 4500 cal yr BP, the vegetation became restiad-dominated, indicating full raised bog conditions. The coarse resolution cuticle results were further compared to a pollen record from the same sequence, which was established independently. This comparison showed that plant subfossil cuticles can provide additional information to pollen analysis in cases where pollen is hard to identify or poorly preserved. Specifically, restiad pollen is hard to differentiate, yet cuticles of Empodisma and Sporadanthus have very distinct features. Also, Cyperaceae pollen is very poorly preserved at Moanatuatua Bog and the Cyperaceae pollen curve shows a poor match with the Cyperaceae cuticle record. It is suggested therefore that Cyperaceae pollen at this site – and potentially other peat sites – is a less reliable indicator of local sedge communities than a Cyperaceae cuticle record. At fine resolution, results were blurred across a time interval that was marginal for reconstructing response patterns due to the constraints imposed by sampling resolution and peat accumulation rate of Moanatuatua Bog. Nevertheless, two out of three charcoal layers recorded a local fire on the bog surface, with one layer displaying the expected vegetation response. After the fire, Empodisma, as a mid-successional species, re-established on the bog surface before Sporadanthus, a late-successional species. The other layer was dominated by sedges and showed no response pattern, as is to be expected due to the very fast recovery of sedges. In general, sample preparation for cuticle analysis proved to be fast with relatively little equipment or chemicals needed. With detailed reference material, identification to species level is possible due to distinctive and pronounced cuticle features. Plant cuticle analysis is therefore proposed to be a reliable tool to reconstruct long-term and short-term vegetation changes from peat sequences.</p>

Investigations of plant subfossil cuticles at a Holocene raised bog complex, northern New Zealand

<p>Subfossil plant cuticles, the very resistant waxy layer covering vascular land plants, are a neglected source of information in peat studies, despite their high preservation and identification potential. A lack of standardised methods and reference material are major contributing factors. In this thesis, a new method is introduced to test if subfossil plant cuticles from Moanatuatua Bog in the northern North Island of New Zealand can give a robust reconstruction of local bog surface vegetation changes during the Holocene. The method was successfully established and applied at coarse sampling resolution to show vegetation changes across the full length of the core and at fine sampling resolution around charcoal layers to reconstruct the post-fire response pattern of the main plant species on the bog. Additionally, bulk density and organic matter analyses were carried out to provide further insight into these changes. At the core site, towards the southern margins of Moanatuatua Bog, swamp forest had developed by 15000 cal yr BP. Until ca. 10500 cal yr BP, the vegetation assemblage was sedge-dominated, indicating swamp and/or fen conditions. A significant increase in macroscopic charcoal particles coincided with the transition to a more diversified vegetation composition. At around 4500 cal yr BP, the vegetation became restiad-dominated, indicating full raised bog conditions. The coarse resolution cuticle results were further compared to a pollen record from the same sequence, which was established independently. This comparison showed that plant subfossil cuticles can provide additional information to pollen analysis in cases where pollen is hard to identify or poorly preserved. Specifically, restiad pollen is hard to differentiate, yet cuticles of Empodisma and Sporadanthus have very distinct features. Also, Cyperaceae pollen is very poorly preserved at Moanatuatua Bog and the Cyperaceae pollen curve shows a poor match with the Cyperaceae cuticle record. It is suggested therefore that Cyperaceae pollen at this site – and potentially other peat sites – is a less reliable indicator of local sedge communities than a Cyperaceae cuticle record. At fine resolution, results were blurred across a time interval that was marginal for reconstructing response patterns due to the constraints imposed by sampling resolution and peat accumulation rate of Moanatuatua Bog. Nevertheless, two out of three charcoal layers recorded a local fire on the bog surface, with one layer displaying the expected vegetation response. After the fire, Empodisma, as a mid-successional species, re-established on the bog surface before Sporadanthus, a late-successional species. The other layer was dominated by sedges and showed no response pattern, as is to be expected due to the very fast recovery of sedges. In general, sample preparation for cuticle analysis proved to be fast with relatively little equipment or chemicals needed. With detailed reference material, identification to species level is possible due to distinctive and pronounced cuticle features. Plant cuticle analysis is therefore proposed to be a reliable tool to reconstruct long-term and short-term vegetation changes from peat sequences.</p>

Paleo-environmental reconstruction of a Late Quaternary organic-rich section preserved near Ohakune, central North Island, New Zealand

<p>A 6m thick section of organic-rich sediment, exposed at Karioi, near Ohakune, central North Island (672m above sea level), presents an opportunity to form a detailed palynological record of Late Quaternary vegetation and climate change. The organic-rich sequence at Karioi lies beneath a 3.29m thick cover-bed sequence that contains towards its base the c. 25.4 ka cal BP Kawakawa/Oruanui Tephra, a key chronostratigraphic marker for the Last Glacial Maximum (LGM) throughout New Zealand. A previous palynological investigation of the underlying organic sediments suggested they extended back from the LGM (Marine isotope stage 2) to the previous interglacial (MIS 5). Such apparently continuous terrestrial records spanning this age range and located at this altitude are rare. A key feature of the Karioi organic sequence is the occurrence of numerous millimetre- to decimetre- thick tephra, derived from a variety of North Island eruptive sources. The possibility that volcanic processes have influenced vegetation change makes climate inferences at this important site potentially problematic. In this new study of the Karioi section, centimetre-scale palynological and diatom sampling conducted above and below three selected tephra (here named ‘Big Lower Lapilli’, ’Unknown’ tephra, and ‘Little’ tephra) at Karioi, were used to assess the influence of these volcanic events on the vegetation and local hydrology. Loss-on-ignition and magnetic susceptibility were used, alongside pollen and diatom analysis, to infer changes in local hydrology and depositional processes in relation to environmental stability. Together, these analyses helped determine the volcanic impacts on vegetation assemblages gained from the pollen record at the site and allowed these to be disassociated from larger scale climate influences of interest. The results of this study indicate a discernible volcanic impact on vegetation and hydrology following just one of the three volcanic events targeted in the record. High-resolution (0.5cm) pollen analysis above and below the largest of the three tephra layers, the 22cm thick ‘Big Lower Lapilli’ showed a notable change in vegetation assemblage immediately following tephra deposition. The most significant of these changes was the marked increase in herbs. This was an unexpected result thought to be due to the proximity of the site to sub-alpine and alpine herbaceous communities, which in turn were closer to the source of volcanism than other vegetation communities depicted in the pollen record. The changes to the pollen spectra are estimated to have taken 300 years to return to pre-eruption assemblages. Magnetic susceptibility and loss-on-ignition results further add to this research by indicating the comparative stability of the depositional environment around the time of deposition of the ‘Big Lower Lapilli’. Statistical analysis further identified a change in vegetation communities associated with tephra deposition, coinciding with an increase in diatom species abundance, which signified an increase in water volume and depth at the site. This was most clearly seen by the marked increase in Aulacoseira ambigua, which is almost exclusively found in water bodies of at least 2 metres depth. These results have major implications for pollen-based climate reconstructions from sequences with interbedded tephra layers. First, such investigations should include fine resolution analyses around prominent tephra layers to test for possible volcanic disturbance that may be a confounding factor in any paleoclimatic reconstructions applied. In this study, for example, vegetation assemblages may have taken up to 300 years to return to pre-eruption levels, but this recovery phase was well within the c. 1000 year inter-sample period of the original coarse (10cm) resolution record. Without the fine resolution study conducted here, the decline of shrubs and increase in grasses, with no obvious changes to trees following deposition of the ‘Big Lower Lapilli’ could have been inferred as a short-term cooling interval. Beyond this restricted zone of volcanic disturbance, greater confidence in the paleoclimatic interpretation of the Karioi pollen record has been achieved as a result of this finer resolution ‘test’ for volcanic disturbance. Second, the volcanic disturbance indicated following the ‘big lower lapilli’ has shed light on pollen taphonomic sources and pathways at this site and in turn, on spatial patterns of vegetation communities. In this case, the increase in tree pollen relative to non-arboreal pollen is interpreted as originating from more distant forest stands that have been comparatively less affected by the deposition of tephra than locally growing vegetation.</p>