Mid- to late-Holocene vegetation history of Greater Exmoor,UK: estimating the spatial extent of human-induced vegetation change

This paper presents the results from three pollen profiles from a group of small spring mire sites on the southern edge of Exmoor in south west England. The size and topography of these sites allow detailed local landscape histories around each site to be reconstructed which broadly cover the mid- to late-Holocene. Comparison of the individual local landscape histories demonstrates the scale of spatial variation in vegetation around the upland edge, and facilitates understanding of human-landscape interactions from the early Neolithic onward. In the early Neolithic significant short-term woodland disturbance is recorded around the upland fringe, including clearance of oak-hazel-elm woodland, suggesting that the shift from Mesolithic to Neolithic is not marked by a gradual environmental transition. Following this, there is clear evidence of Neolithic management of upland heath using fire, presumably for the management of upland grazing. Woodland clearances are recorded throughout the later Prehistoric period; however, the use of multiple profiling suggests that woodland clearance is spatially discrete, even within an area of 4 km². Pastoral land use is dominant around the uplands until around 900–1,000 a.d., and there is no discernible Roman or post-Roman period impact in the vegetation, suggesting cultural stability from the late Iron Age to the early Medieval period. By 1,100 a.d., there is a shift to mixed arable-pastoral farming which appears to continue well into the post-Medieval period.     

Mid- and late-Holocene vegetation history and tephra studies at Fenton Cottage, Lancashire, U.K.

The Over Wyre region of Lancashire, England, was formerly dominated by a complex of ombrotrophic intermediate raised mires, most of which have been severely damaged by agricultural activity during the last 250 years. The degree of truncation and desiccation of the remaining peats means that opportunities for studying environmental history in this part of lowland England are extremely rare. An exception occurs at Fenton Cottage where a relict, non-truncated portion of original mire survives and forms an environmental archive spanning the second half of the Holocene. The palaeoecological record shows that there has been a continual human influence on the development of the landscape since the mire began growing, with a particularly significant deforestation episode commencing in the late Iron Age. A major expansion of the mire system commenced in the late Bronze Age/early Iron Age and may have led to the abandonment of settlement in and around the peatlands during much of the Iron Age. The investigation also yielded the first tephra to be discovered in English peats. This took the form of a discrete layer of microscopic tephra, geochemically assigned to the Icelandic Hekla-4 eruption of ca. 2300 cal. B.C.. This was recorded inScheuchzeria palustris-dominated peat which formed during a period of freshwater flooding. The find represents the most southerly geographical location in the British Isles where Hekla-4 tephra has been detected to date. The study demonstrates the palaeoecological value of threatened relict lowland peat archives in agricultural landscapes and highlights the potential of tephrochronology as a tool for studying environmental changes and wetland archaeology in southern Britain.     

Similarities and dissimilarities,synchronisms and diachronisms in the Holocene vegetation history of the Balearic Islands and Sicily

In some continental and island sites in the western Mediterranean basin, the Holocene vegetation and climate dynamics seem to show the same patterns in time and space. Nevertheless, different synchronous scenarios have been proposed from other south European, North African and Near Eastern pollen records from around the Mediterranean basin. Striking similarities and synchronisms have been found between Sicily and the Balearic Islands. These islands, although under different bioclimatic influences, show similarities in the main trends of vegetation and climate dynamics during the Post-glacial. Lago di Pergusa is the only natural inland lake in Sicily and because of its geographical location, has a good potential sensitivity to the climatic changes of the Mediterranean basin. Likewise, coastal sediments from Minorca and Majorca, the Balearic Islands, have similar peculiarities. The present-day environmental situation, now that most of the natural vegetation in these islands has disappeared, has been brought about either by a climatic trend towards increasing aridity or an increase in human activities. It seems clear that prehistoric human people alone could not have caused all the environmental changes recorded in the last millennia in both places.     

On the Holocene vegetation history of the Argive Plain (Peloponnese,southern Greece)

Palynological investigations have been carried out on a sediment core from ancient Lake Lerna, a former fresh water lagoon in the western part of the Argive plain, Peloponnese, southern Greece. The sequence starts at 6800 B.P. (5700 cal B.C.). The lowest part of the pollen diagram shows a period of open deciduous oak woods, which may have been influenced by human impact already (Zone I). It is followed by a period of dense deciduous oak woods (Zone II), which lasted until the beginning of the Bronze Age ca. 4800 B.P. (3500 cal B.C.). Later, the diagram indicates strong human influence such as woodland clearance, the spread of maquis, phrygana and pine in Zones IIIa-IV. During the Archaic, Geometric and Classical periods after ca. 2700 B.P. (800 cal B.C.) there is evidence of a phase of extensive olive farming (Zone IIIb). In the same zone, after a period of scattered finds, there is an almost continuous Juglans curve. Zone IV is characterised by high pine values. In Zones I-II the evidence of evergreen Mediterranean plants is surprisingly small. In times with no discernible human influence (Zone II), deciduous oaks dominate, with no evidence for a climax vegetation of the Oleo-Ceratonion alliance. Olea europaea is the only species of that alliance traceable by its pollen in the diagram, while Ceratonia pollen is totally absent.     

Organic matter distribution and fluxes within a holm oak (Quercus ilex L.) stand in the Etna volcano

Located at 1100 m above sea level, on the western site of the Etna volcano, the ecophysiology of the Mount Minardo holm oak coppice has been investigated for more then twenty years. In this stand, now 31 years old, the above ground biomass amounts to 15000 g m^-2 of organic material, including leaves and perennial woody material. During these 31 years, the mean annual production has been around 775 g m^-2. The yearly mean litterfall amounts to 310 g m^-2, including 200 g m^-2 of leaves, mostly two years old. The soil surface is covered by a litter layer amounting to 3150 g m^-2. Each year, following Jenny's decomposition rate and field measurements, 290 g m^-2 of the litter turns into CO₂, or becomes incorporated in the soil organic matter.     

Charcoal analysis, a method to study vegetation and climate of the Holocene: The case of Lago di Pergusa (Sicily, Italy)

The direct comparison between microcharcoal and pollen data from the Holocene sediment core of Lago di Pergusa (central Sicily, Italy) led us to investigate the linkages between fire, vegetation, and climate in the Mediterranean Basin. The role of human populations in shaping the environment of the last millennia was closely examined as well. Pollen and charcoal were extracted using a standard pollen methodology and both identified from the same pollen slides. At Lago di Pergusa the importance of fire in maintaining and favouring a Mediterranean vegetation, a basic concept in ecology, seems to be inconsistent, as important fires took place in the open environments with xeric vegetation at the beginning of the Holocene well before the expansion of evergreen vegetation. On the contrary some big fires seem to have happened in the period (around 8000 years BP) in which the greatest wetness, the thickest forest canopy, and the most important expansion of submontane vegetation of the record are found. A probable explanation of this phenomenon can be found in the precipitation regime, in the increased available biomass and in the resulting increase in combustible material, indicating also that the highest humidity achieved in central Sicily during the Holocene was not strong enough to prevent fires. During this period drops in arboreal pollen concentration match in minima in the charcoal curves. Fires were practically absent during the Neolithic and Eneolithic periods and not responsible for the general trend towards aridification identified in the pollen record, at times in which prehistoric populations are generally believed to have caused forest clearance by burning. Important and frequent burnings are documented for the Bronze and Iron Ages and probably not all of them were fires of living trees, but burning of wood for producing metals, cooking or heating. The occurrence of a fire around 3700 years BP temporarily caused a minor decrease of arboreal pollen concentration. In the open landscapes of the two last millennia an almost continuous sign of regional burnings is recognized, confirming the historical evidence of an intense land use in central Sicily at least since Roman times.     

Litter quality and decomposition in a CO2-enriched Mediterranean forest ecosystem

Six large open top chambers were installed to test the effect of atmospheric [CO₂] enrichment on clumps of natural Mediterranean vegetation starting from early spring 1992. To study the impact of [CO₂] enrichment on litter decomposition, leaves of three woody species (Quercus ilex L., Phillyrea angustifolia L. and Pistacia lentiscus L.) were collected from the forest floor and subsequently incubated in situ over a two-year period. The initial slope of the exponential function, describing mass loss, indicated that there was a small negative effect of elevated [CO₂] on the decomposition rate of all the species. All regressions were significant. The decrease of decomposition rate is particularly notable during the initial stages of decomposition, when the differences of quality parameters, lignin/N and C/N were larger. This study points out that a decrease of decomposition rate may occur under elevated [CO₂] conditions; if this effect is coupled to an increase of primary production, there will be a net rise of C-storage in the soils of forest ecosystems. Forest soils may, therefore, represent a potentially increasing sink for this excess carbon. This revised version was published online in June 2006 with corrections to the Cover Date.     

Middle to Late Holocene vegetation history of the Upper Engadine (Swiss Alps): the role of man and fire

To reconstruct the vegetation and fire history of the Upper Engadine, two continuous sediment cores from Lej da Champfèr and Lej da San Murezzan (Upper Engadine Valley, southeastern Switzerland) were analysed for pollen, plant macrofossils, charcoal and kerogen. The chronologies of the cores are based on 38 radiocarbon dates. Pollen and macrofossil data suggest a rapid afforestation with Betula, Pinus sylvestris, Pinus cembra, and Larix decidua after the retreat of the glaciers from the lake catchments 11,000 cal years ago. This vegetation type persisted until ca. 7300 cal b.p. (5350 b.c.) when Picea replaced Pinus cembra. Pollen indicative of human impact suggests that in this high-mountain region of the central Alps strong anthropogenic activities began during the Early Bronze Age (3900 cal b.p., 1950 b.c.). Local human settlements led to vegetational changes, promoting the expansion of Larix decidua and Alnus viridis. In the case of Larix, continuing land use and especially grazing after fire led to the formation of Larix meadows. The expansion of Alnus viridis was directly induced by fire, as evidenced by time-series analysis. Subsequently, the process of forest conversion into open landscapes continued for millennia and reached its maximum at the end of the Middle Ages at around 500 cal b.p. (a.d. 1450).     

Canopy structure within a Quercus ilex forested watershed: variations due to location,phenological development,and water availability

Spatial and temporal changes in canopy structure were studied in 1988 and 1989 in a Mediterranean Quercus ilex forest in north-eastern Spain. Due to differences in precipitation patterns the 1989 growing season was drier than the 1988 growing season. Sampling was conducted in parallel at two sites which represent endpoints along a slope gradient within a watershed (ridge top at 975 m, and valley bottom at 700 m). At both sites, similar inter-annual changes in canopy structure were observed in response to differences in water availability. Samples harvested in the upper 50 cm of the canopy during 1989 exhibited a decrease in both average leaf size and the ratio of young to old leaf and stem biomass relative to samples obtained in 1988. At the whole canopy level, a decrease in leaf production efficiency and an increase in the stem to leaf biomass ratio was observed in 1989. Temporal changes in canopy leaf area index (LAI) were not statistically significant. Average LAI values of Q. ilex at the two sites were not significantly different despite differences in tree stature and density (4.6 m² m^–2 at the ridge top, and 5.3 m² m^–2 at the valley bottom). Vertical distribution of leaves and stems within the canopy was very similar at the two locations, with more than 60% of the total LAI in the uppermost metre of the canopy. The possible significance of such an LAI distribution on the canopy carbon budget is discussed.     

Mid to late Holocene vegetation and land use history in the Weald of south-eastern England: multiple pollen profiles from the Rye area

The High Weald is an unusually well-wooded area in southern England. A high proportion of this woodland is ancient, being formerly exploited as seasonal pasture and coppice. Multiple pollen profiles from the Rye area have been used to elucidate the origins of this cultural landscape. By combining sites with small and large pollen source areas, both local and regional patterns of vegetation change have been determined. The mid-Holocene Tilia-dominated woodlands were subjected to temporary clearance as early as the Neolithic. This woodland was more extensively exploited over a ca. 700 year period from the beginning of the Bronze Age. The main elements of the modern landscape (woodland, pasture and limited cultivation) can be traced back to a more intensive phase of human activity, which commenced in the late Bronze Age. A regional increase in Fagus sylvatica pollen ca. 750 B.C. probably reflects the use of the Wealden woods for pasturage. There is no palynological evidence that the fuel demands of the Roman iron industry resulted in widespread woodland destruction. The early Anglo-Saxon period appears to have been one of land-use continuity, with a second increase in Fagus pollen at ca. A.D. 700 corresponding to historical evidence for the presence of wood-pastures in the Weald.     

Heat requirement for the onset of the Olea europaea L. pollen season in several sites in Andalusia and the effect of the expected future climate change

Olives are one of the largest crops in the Mediterranean region, especially in Andalusia, in southern Spain. A thermal model has been developed for forecasting the start of the olive tree pollen season at five localities in Andalusia: Cordoba, Priego, Jaen, Granada and Malaga using airborne pollen and meteorological data from 1982 to 2001. Threshold temperatures varied between 5°C and 12.5°C depending on bio-geographical characteristics. The external validity of the results was tested using the data for the year 2002 as an independent variable and it confirmed the models accuracy with only a few days difference from predicted values. All the localities had increasingly earlier start dates during the study period. This could confirm that olive flower phenology can be considered as a sensitive indicator of the effects of climate fluctuations in the Mediterranean area. The theoretical impact of the predicted climatic warming on the olives flowering phenology at the end of the century is also proposed by applying Regional Climate Model data. A general advance, from 1 to 3 weeks could be expected, although this advance will be more pronounced in mid-altitude inland areas.     

Clinical significance of allergic sensitization toOlea europaea L. pollen in Naples area,Italy

Summary The aim of this study is the evaluation of clinical significance of the allergic sensitization toOlea europaea L. pollen allergens in the Naples area, because in the last 10 years an increasing frequency of IgE mediated sensitization to these allergens has been observed. 4124 patients of both sexes (2989 adults and 1153 children) consecutively examined in our Allergological Center from January 1, 1988 to December 30, 1989 have been considered in this study. The patients were selected on the basis of a history of rhinitis (R) and/or asthma (A) and were evaluated by clinical examination, SPT, RAST and specific or aspecific BPT. Among 2267 adults and 879 children sensitized to almost one aeroallergen we found respectively 306 (13.49%) and 75 (8.53%) subjects with an allergic sensitization toOlea europaea L. pollen. The frequency of clinical manifestation was respectively R+A (58.16%), R (39.54%), A (2.28%) in adults; R+A (61.33%), R (26.66%), A (12%) in children. A monosensitization toOlea europaea L. pollen was found in 1.33% of children and in 2.28% of adults examined. The association with other allergens especially with mites and/or other pollen was very common.     

Litterfall as a measure of primary production in Mediterranean holm-oak forest

In this paper we discuss the use of litterfall as a method to measure primary production and its between year relation to climatic fluctuation. Seven years of study in a mediterranean holm-oak forest showed a moderate inter-annual variability of litterfall (C.V. 11%), while the annual variability of the actual evapotranspiration was three times higher (C.V.30%). Furthermore, the inter- and intra-annual variability of nutrient content in the various fractions are presented in relation to water availability. Monthly and seasonal variability was higher than the annual variability for all analyzed elements.     

Tree growth,mortality, and above-ground biomass accumulation in a holm oak forest under a five-year experimental field drought

A holm oak forest was exposed to an experimental drought during 5 years to elucidate the growth responses of the dominant species Quercus ilex, Arbutus unedo and Phillyrea latifolia. Soil water availability was partially reduced, about 15% as predicted for this area for the next decades by GCM and ecophysiological models, by plastic strips intercepting rainfall and by ditch exclusion of water runoff. The stem diameter increment was highly correlated with annual rainfall in all species, and drought treatment strongly reduced the diameter increment of Q. ilex (41%) and specially of A. unedo (63%), the species showing higher growth rates. Stem mortality rates were highly correlated with previous stem density, but drought treatment increased mortality rates in all species. Q. ilex showed the highest mortality rates (9% and 18% in control and drought plots, respectively), and P. latifolia experienced the lowest mortality rates (1% and 3% in control and drought plots, respectively). Drought strongly reduced the increment of live aboveground biomass during these 5 years (83%). A. unedo and Q. ilex experienced a high reduction in biomass increment by drought, whereas P. latifolia biomass increment was insensitive to drought. The different sensitivity to drought of the dominant species of the holm oak forest may be very important determining their future development and distribution in a drier environment as expected in Mediterranean areas for the next decades. These drier conditions could thus have strong effects on structure (species composition) and functioning (carbon uptake and biomass accumulation) of these Mediterranean forests.     

The Holocene history of vegetation and settlement at the coastal site of Lake Voulkaria in Acarnania, western Greece

A palynological investigation of a Holocene profile from Lake Voulkaria, western Greece, was carried out as a contribution to the environmental history of the coastal area of northwestern Acarnania and the Classical city of Palairos. It shows that deciduous oaks dominated the natural vegetation of the area throughout the Holocene. Until ca. 7000 B.C. Pistacia occurred abundantly, while other evergreen woody taxa were rare. At ca. 6300 B.C. an expansion of Carpinus orientalis/Ostrya can be observed. Around ca. 5300 B.C. spreading of Erica indicates a change to a drier climate and/or first human impact. Since ca. 3500 B.C. an increase of evergreen shrubs now clearly indicates land-use. The foundation of the Classical city of Palairos led to a temporary expansion of Phillyrea maquis. Within this period, molluscs of brackish water indicate the use of the lake as a harbour after the construction of a connection to the sea. The deciduous Quercus woodland recovered when human impact decreased in the area, and lasted until modern times.     

Economically important seaweeds in Mar Piccolo,Taranto (southern Italy): a survey

A preliminary survey was carried out of the marine algae in the Mar Piccolo Basin, Taranto (southern Italy), in order to assess the degree of sewage pollution and to determine the presence of any economically important species that might be productively utilized. The following commercial species, belonging to a drift algal community, were found: Gracilaria bursapastoris, G. cf. verrucosa, Solieria sp. and S. filiformis. The species showed an aggregated distribution within the community and a clear cyclic annual pattern. Gracilaria bursa-pastoris exhibited the highest mean biomass values in May, whereas Solieria spp. were the most abundant in October. At the present time, only the harvesting of G. bursa-pastoris appears profitable. However, further detailed studies are required to more fully assess the standing crop of the Solieria spp. and G. cf. verrucosa. Considering the environmental situation in the basin, it might be more appropriate to cultivate, rather than harvest, these commercially important seaweeds. With the large number of sewage outlet plants available in the basin, the cultivation of seaweeds in a wastewater treatment-aquaculture system should be considered.     

Towards the vegetation and settlement history of the southern Dobrudza coastal region, north-eastern Bulgaria: A pollen diagram from Lake Durankulak

Palynological investigation and radiocarbon dating of a 6-m core from lake Durankulak, north-eastern Bulgaria, enables vegetation development and human occupation from ca. 5500–5300 cal. B.C. onwards to be traced. Steppe vegetation that included with groves of deciduous trees asQuercus, Ulmus, Carpinus belulus andCorylus changed to a forest-steppe after 4000 cal. B.C. The archaeopalynological record indicates three distinct phases of human activity as follows: (1) 5300–4200 cal. B.C. (late Neolithic and Eneolithic) during which farming, that included a substantial arable component, was pursued, (2) 3500–3000 cal. B.C. (transition to early Bronze Age) when stock rearing appears to have dominated, and (3) after 1300 cal. B.C. (late Bronze Age) when arable farming again assumed importance. The palynological data correlate well with the rich archaeological record for human settlement that is available for the region from late Neolithic times onwards.     

Quercus ilex facing water stress: a functional equilibrium hypothesis

A boundary line analysis of the scatterplot relating pre-dawn leaf water potential to pre-dawn minus minimum leaf water potential was applied to study the efficiency of the Mediterranean evergreen oak species to buffer the effects of variability in water resources. The results are discussed in term of stomatal regulation and changes in soil-to-leaf hydraulic conductance of water flow, both induced by changes in leaf water potential. For this purpose, we used data for leaf water potential measured in three stands of Quercus ilex across a soil water availability gradient in Southern France, and two others obtained in California and Arizona for Quercus turbinella and Portugal for Quercus coccifera. A classification of plant responses from mesic to xeric sites is proposed.     

Comparison between the allergenic airborne pollen in Trieste and at Lozzo di Cadore (Italy) in 1989

Summary A comparative study was carried out between aeroallergenic pollen spectra in Trieste and at Lozzo di Cadore. The two localities were found to be different on a five-day running mean basis as to the 8 pollen taxa monitored by the National Aerobiological Monitoring Network managed by the Italian Association of Aerobiology (AIA). In the zone of Lozzo the pollination curve of the spring flowering taxa showed a lag of about one month due to the colder climate. Lozzo di Cadore showed a poor airborne pollen content,Corylus and Graminaceae being prevailing. Trieste has a higher airborne pollen diversity and longer pollination times because of its higher floristic and vegetational complexity. In Trieste the allergenic pollen spectrum showed great quantities ofOstrya, Quercus, Oleaceae, Graminaceae and of ruderal taxa, widespread over the area, due to man's influence.