Holocene altitudinal shifts in vegetation belts and environmental changes in the Sierra Madre Occidental, Northwestern Mexico, based on modern and fossil pollen data

A modern pollen rain study was performed in a 300 km-long altitudinal transect (~ 28° N latitude) from 300 to 2300 m elevation. The higher elevation modern communities: epithermal oak–pines, pine–oak forest, pine forest, and mixed conifer forest were easy to distinguish from their pollen content. In contrast, lower elevation subtropical communities: thornscrub and tropical deciduous forest were difficult to separate, because they share many pollen taxa. Nevertheless we identify high frequencies of Bursera laxiflora as an important component of the tropical deciduous forest.Additionally, fossil pollen was analyzed at three sites located between 1700 and 1950 m altitude at ~ 28° latitude north in the Sierra Madre Occidental of northwestern Mexico. The sites were in pine–oak (Pinus–Quercus), pine, and mixed-conifer forests respectively. Shifts in the altitudinal distribution of vegetation belts were recorded for the last 12,849 cal yr BP, and climate changes were inferred. The lowest site (pine–oak forest) was surrounded by pine forest between 12,849 and 11,900 cal yr BP, suggesting a cold and relatively dry Younger Dryas period. The early Holocene was also cold but wetter, with mixed conifer forest with Abies (fir) growing at the same site, at 1700 m elevation, 300 m lower than today. After 9200 cal yr BP, a change to warmer/drier conditions caused fir migration to higher elevations and the expansion of Quercus at 1700 m. At 5600 cal yr BP Abies was growing above 1800 m and Picea (spruce) that is absent today, was recorded at 1950 m elevation. Fir and spruce disappeared from the 1950 m site and reached their present distribution (scattered, above 2000 m) after 1000 cal yr BP; we infer an episodic Holocene migration rate to higher elevations for Abies of 23.8 m/1000 cal yr and for Picea of 39.2 m/1000 cal yr. The late Holocene reflects frequent climate oscillations, with variations in the representation of forest trees. A tendency towards an openness of the forest is recorded for the last 2000 yrs, possibly reflecting human activities along with short-term climate change.     

History of Late Holocene vegetation at Quintana Roo,Caribbean coast of Mexico

A pollen record of a Late Holocene sediment core from the Mexican Caribbean coast (Quintana Roo) shows the development and changes of a mangrove system. Humid conditions seem to have persisted for the period approximately 2500–1500 ¹⁴C yr BP (pollen zone I), and mangrove Rhizophora mangle dominated with a good representation of elements from the nearby semi-evergreen tropical forest. During the period approximately 1500–1200 ¹⁴C yr BP (pollen zone II) the mangrove Conocarpus erecta dominated. R. mangle almost disappeared and other taxa appeared, suggesting drier climatic conditions and generally more open vegetation. This dry period coincided with the period of the Maya cultural decline. The following period (pollen zone III, approximately 1200–1000 ¹⁴C yr BP) was characterized by the recovery of R. mangle, indicating more humid conditions than in the preceding pollen zone. Pollen zone IV (approximately 1000 ¹⁴C yr BP till present) suggests a drier period reoccuring with C. erecta; this marks the transition to present day conditions.     

Long-term dynamics of vegetation and disturbance of a southern boreal spruce swamp forest

Abstract. Analysis of pollen, charcoal and loss-on-ignition in peat cores from a Picea aèies-dominated swamp forest in central Sweden show the vegetation changes and disturbance patterns over 9500 yr. Six major sequences of local vegetation development are identified: (A) Pinus period, ca. 9500–7000 cal. BP; (B) Open mire period (ca. 7000–4500 cal. BP; (C) Betula period, ca. 4500–2300 cal. BP; (D) Picea period (ca. 2300–1000 cal. BP; (E) Human impact period (ca. 1000–100 cal. BP); and (F) Period of human abandonment during the last ca. 100 yr. The swamp forest has been highly dynamic in response to various natural and anthropogenic disturbance agencies. Several fires have heavily influenced the vegetation development. During the last ca. 900 yr human influence has been important, initially from grazing and trampling by domesticated animals (ca. 1000–500 cal. BP), and subsequently small-scale cereal growing (ca. 400–100 BP). Cutting, burning and animal browsing influenced the structure and dynamics of the swamp forest by creating a more open stand and suppressing tree regeneration. Recent cessation of human impact has led to increased tree regeneration and a denser swamp forest stand. The present high biodiversity, and subsequent conservation interest does not result from long-term stability or absence of fire and human impact. However, in spite of repeated disturbances, a continuity of old and senescent trees produced a forest type with abundant dead wood. With the relatively minor importance of fire over long periods of time, the swamp forest developed a structure maintaining a high biological diversity. An important issue for maintaining long-term biodiversity in the boreal landscape must be to create a mosaic where different forest types are present, with a variety of structures, substrates and processes, to provide a certain degree of freedom for species to move around in the landscape.     

Distribution and conservation significance of endemic species of flowering plants in Peru

Using the data published in the Catalogue of the Flowering Plants and Gymnosperms of Peru, we analyzed the elevational distributions of 5323 species reported as endemics from that country as a whole, for 10 families with the highest number of endemic taxa in Peru, and the distribution patterns of these species according to life form. We calculated the density of endemism (number of endemic species divided by area × 1000) and absolute number of endemic species among life forms and families, along an elevational gradient. Overall densities of endemics were 10–15 times higher at mid-elevation (2000–3500 m) than in the Amazonian lowlands (0–500 m). Absolute numbers of endemics peaked at 1500–3000 m for herbs, shrubs, and epiphytes, while trees, vines, and lianas showed maxima in the lowlands (0–500 m); yet densities of endemics for all life forms peaked at 1500–3000 m. Among the 10 families with the highest number of endemics, densities of endemics peaked at mid- to high elevation (1500–4500 m), but showed much disparity in the elevational distribution of absolute numbers of endemic species. Finally, the percentage of endemic species to total species is highest for herbs, shrubs, and epiphytes. Given that less than 10% of the land area for each of the montane zones (2000–4500 m) is protected compared to 13.5–29.9% in the lower elevations (0–1000 m), we recommend that priority be given to increasing the size of protected areas at mid- to high altitude in the Andean slopes to grant further protection in zones with the highest density of endemics. We also recommend that more emphasis be given to collecting and studying non-trees, since most endemic species belong to that class.     

Vegetation history with implication of climate changes and human impacts over the last 9000 years in the Lake Nanyi area,Anhui Province,East China

Palynological analyses in combination with radiocarbon dating on a Holocene borehole from the Lake Nanyi, Anhui Province, East China demonstrate a well-documented local vegetation evolution since 9000 cal BP, which is the first record of Holocene climate change and human impact in this region. Since 9000 cal BP a mixed evergreen and deciduous broad-leaved forest dominated by Cyclobalanopsis and Quercus developed in this area, indicating a warm climate condition with enhanced insolation. A mixed evergreen and deciduous broad-leaved forest was fully developed between 6600–4500 cal BP, which corresponds to the Holocene Climate Optimum with the strong influence of East Asian summer monsoon (EASM). After 3000 cal BP the broad-leaved forest decreased rapidly, while land herbs and ferns increased. It seems that the climate condition in East China was similar to the present after Holocene Climate Optimum. Pollen results show a potential interface between environment changes and human activities. Pollen diagram demonstrates that human impacts on the natural vegetation remained weak at the early stage but significantly enhanced upwards. The distinctive fluctuations of the pollen contents among AP (trees and shrubs), and the possible agriculture indicators might infer the potential human behaviors for environment changes. Due to the enlargement of organized farming and increase in population, natural forest was eventually replaced by farmland since 3000 cal BP. This study would increase our knowledge of Holocene vegetation transition related to the monsoon dynamics on a long timescale in East China and provide an environmental background for more detailed studies on cultural developments in the middle and lower reaches of the Yangtze River region.     

The bog climax hypothesis: fossil arthropod and stratigraphic evidence in peat sections from southeast Alaska, USA

The hypothesis that bogs are climax (structurally and compositionally stable) communities has been proposed for several large regions including southeast Alaska. A logical consequence of the bog climax is the hypothesis that, where there is infrequent large-scale physical disturbance, landscape-level changes from early successional woodland to late successional peatland should have occurred during the Holocene. This hypothesis is tested in southeast Alaska using analyses of fossil arthropods and site stratigraphy, as well as a review of the ecological literature.
Results indicate at least three major landscape types have dominated since deglaciation: deciduous woodland (about 9000 to 6000 yr BP), coniferous woodland (about 6000 to 3000 yr BP), and peatland (about 3000 yr BP to present). Other paleoecological and ecological studies from around the region provide evidence for directional changes, both past and present, from woodland to peatland. Furthermore, there is no clear evidence for peatland to woodland transitions in the absence of large-scale disturbance. These results suggest that the bog climax hypothesis deserves a more careful examination by ecologists studying succession.     

Late‐glacial and Holocene vegetation,climate and fire dynamics in the Serra dos Órgãos,Rio de Janeiro State,southeastern Brazil

We present a high‐resolution pollen and charcoal record of a 218 cm long sediment core from the Serra dos Órgãos, a subrange of the coastal Serra do Mar, located at 2130 m altitude in campos de altitude (high elevation grass‐ and shrubland) vegetation near Rio de Janeiro in southeastern Brazil to reconstruct past vegetation, climate and fire dynamics. Based on seven AMS ¹⁴C ages, the record represents at least the last 10 450 ¹⁴C yr bp (12 380 cal years bp ), The uppermost region was naturally covered by campos de altitude throughout the recorded period. Diverse montane Atlantic rain forest (ARF) occurred close to the studied peat bog at the end of the Late‐glacial period. There is evidence of small Araucaria angustifolia populations in the study area as late as the early Holocene, after which point the species apparently became locally extinct. Between 10 380 and 10 170 ¹⁴C yr bp (12 310–11 810 cal yr bp ), the extent of campos de altitude was markedly reduced as montane ARF shifted rapidly upward to higher elevations, reflecting a very wet and warm period (temperatures similar to or warmer than present day) at the end of the Younger Dryas (YD) chronozone. This is in opposition to the broadly documented YD cooling in the northern Hemisphere. Reduced cross‐equatorial heat transport and movement of the Intertropical Convergence Zone over northeastern Brazil may explain the YD warming. Markedly extended campos de altitude vegetation indicates dry climatic conditions until about 4910 ¹⁴C yr bp (5640 cal yr bp ). Later, wetter conditions are indicated by reduced high elevation grassland and the extension of ARF into higher elevation. Fire frequency was high during the early Holocene but decreased markedly after about 7020 ¹⁴C yr bp (7850 cal yr bp ).     

Role of man in the history of vegetation of the Ellero valley (maritime Alps, Italy)

The pollen analysis of a sediment core from a peat bog (Rifugio Mondovi) at the mountain belt (1760 m) in the Ellero Valley (Italian Maritime Alps) shows the postglacial vegetation history. The sequence starts at 12,000 BP during a peak of pine pollen; this first phase shows a low representation of birch and the presence of Tilia. Younger Dryas is characterised by increasing percentages of Artemisia, showing the presence of deciduous Quercus, fir and beech. Elm appears at the beginning of the Holocene during the second pine peak (9800 BP). A 3000-year hiatus is present. Sedimentation resumes at 6000 BP in a Rhododendron fir-wood. The present timberline at 1500 m, at the limit of the beech wood, is a result of the decline of the fir-wood at 2600 BP, which allowed an expansion of beech. During this period, there was a continual increase in Gramineae and deciduous oak and the first occurrences of evergreen oak are observed. The development of larch occurs at 1800 BP, together with walnut, chestnut, cereals and vine.     

Late- and postglacial history of lakes of the Karelian Isthmus

The Late Pleistocene and Holocene history of five lakes in the central part of Karelian Isthmus, south of the present Vuoksi River, are described on the basis of sediment stratigraphical investigations. Two of the Lakes, Michurinskoe (94 m a.s.l.) and Uzornoe (55 m a.s.l.) are situated in an upland area that remained dry land after the deglaciation even during the early high water stages of the Baltic Sea (Baltic Ice Lake until c. 10 000 yr BP and Ancylus Lake 9500–8800 BP). The low-lying central parts of the Isthmus were flooded by the outflow of Lake Ladoga that took place across this area until the formation of Neva River, c. 3 100 yr BP, and further by the waters of River Vuoksi that started flowing into the area from the NW c. 5000 yr BP as a new outlet of Lake Saimaa. The basins of the lakes Krasnoe and Vishnevskoe (both 16 m a.s.l.) became isolated when River Neva was formed and Lake Ladoga sank to its present level. Lake Rakovoe (12 m a.s.l.) was on the level of River Vuoksi up until the mid-19th century, when water level in the central stretch of the river was artificially lowered. Each of the lakes has been variously affected by hydrological and climatic changes and consequences of human activities, e.g. eutrophication due to intensified land use. As a consequence to artificial lowering, done in order to gain field and meadowland, the large, shallow Lake Rakovoe has been largely overgrown by macrophytic vegetation.     

A 37,500-year pollen record from Lake Malaŵi and implications for the biogeography of afromontane forests

Abstract. Two 10-metre cores were analysed and a 37,500 year pollen stratigraphy was established for Lake Mala?i. A lowstand from 37,500 to 35,900 BP indicates extremely dry conditions. From 35,900 to 34,000 BP montane forests were widespread indicating cold, moist climate. Between 34,000 and 26,400 BP warm and dry conditions prevailed and forest area decreased. During the Last Glacial Maximum montane forest was widespread in the catchment, although woodlands apparently persisted at low altitudes: the expansion of the montane forest indicates that the aridity that affected equatorial Africa during this time period did not affect the Lake Mala?i Catchment. The cold and relatively moist conditions during the Late Pleistocene probably allowed biotic interchange between the highlands of East and West Africa via the highlands along the Zaire—Zambezi watershed and among now-isolated islands of Afromontane vegetation in the Lake Mala?i catchment. The Holocene is characterized by climate and vegetation quite similar to today, with indications of slightly wetter conditions between 6150 and 3000 bp and slightly drier conditions between 8000 and 6150 bp . The low percentages of montane forest pollen throughout the Holocene support the hypothesis that the montane grasslands of Mala?i are not recently anthropogenic.     

Vegetation dynamics in central Africa since 18,000 yr BP: pollen records from the interlacustrine highlands of Burundi, Rwanda and western Uganda

A standardized analysis of palaeoecological data, in the form of six pollen sequences and forty- four radiocarbon ages, has permitted a region-wide reconstruction of Late Quaternary vegetation dynamics for the interlacustrine highlands of central Africa.
A landscape widely dominated by ericaceous scrub and grasslands, but also supporting sparse patches of open-canopied montane forest, possibly in those areas with a topography most favourable to the growth of trees, is indicated for the last glacial maximum of 18,000 yr bp . Major expansions in the extent of upper altitudinal forms of montane forest occurred from around 12,500 yr bp , while lower moist montane forest—the expected climax for much of the region today—did not become prominent until 11,000 yr bp to 10,000 yr bp . From the palaeoecological evidence at least, it appears that the major east Central forest refuge, proposed by some workers on the basis of current species' distribution patterns, did not extend to the eastern flanks of the Albertine Rift.
A late glacial–early Holocene transition is only fully chronicled in two of the sites. However, it appears that the expansion of lower montane forest had a time-transgressive pattern across the region, and was not simply from low to high altitude. The composition of forests during the early Holocene appears to have been different to that in the later stages of the present interglacial, as taxa presently associated with wetter and/or more open forest types were much more common. Pollen data also indicate that higher altitude parts of the interlacustrine highlands were more attractive to the earliest (possibly Bantu-speaking) farmers and metal-workers. There is evidence of wide-spread forest clearance around the beginning of the present millennium, possibly as a result of substantial changes in socio-economic conditions, and patterns of settlement, associated with the onset of the Late Iron Age.     

Pollen–vegetation relationships along steep climatic gradients in western Amazonia

Question: How accurately do Amazonian montane forest pollen spectra reflect the vegetation? Can compositional changes observed in the vegetation along environmental gradients be identified in the pollen spectra? How well do herbarium collection data and bioclimatic envelopes represent abundance changes along elevation gradients? Location: Amazonian montane forests, Peru. Methods: Moss polsters collected along five altitudinal transects spanning over 3000 m a.s.l. were used to characterize pollen spectra. Vegetation plot data from a network of 15 1‐ha permanent plots were used to correlate pollen spectra with present‐day vegetation. Probability density functions (PDFs) fitted to pollen and plot data allowed comparisons using Spearman correlation coefficients. Ordination analyses were used to summarize changes in pollen spectra. Correlations between pollen‐based PDFs and previously‐published herbarium collection PDFs were also evaluated. Results: Pollen spectra closely reflected changes in species composition along elevation gradients. A mid‐elevation shift in pollen spectra was identified using ordination analyses. Pollen spectra from the driest forest in our data set were statistically different from those of wet forests. Pollen abundance PDFs along the altitudinal gradient were significantly correlated (P<0.01) with PDFs fitted to plot abundance, basal area and herbarium collection data for ten out of 11 taxa analysed. Conclusions: Pollen spectra closely reflected the vegetation composition of Amazonian montane forests. The differentiation of pollen spectra from dry localities showed the potential of genus‐level pollen data to reflect precipitation gradients. Pollen spectra also reflected mid‐elevation compositional changes well along the lower elevation limit of ground cloud formation. Despite collection biases, herbarium‐based bioclimatic envelope PDFs also represented well forest compositional changes along elevation gradients.     

Habitat change and trade explain the bird assemblage from the La Chimba archaeological site in the northeastern Andes of Ecuador

The nature of tree‐line habitats in the Andes has long been a contentious topic in the ecological literature. Palynological studies suggest that a combination of anthropogenic and natural processes throughout the Holocene contributed to its present form and species composition. This is the first study to use zooarchaeological evidence to reconstruct possible prehistoric changes in these alpine habitats. I analysed the remains of birds from the La Chimba archaeological site in northern Ecuador to assess changes in the bird tree‐line community over three distinct phases (Early, 2640–2390 year BP; Middle, 2390–1994 year BP; Late, 1994–1700 year BP) of this prehistoric settlement. The elevation of this site (3200 m) places it near a steep elevational gradient in vegetation, with the modern tree‐line here at 3500–3600 m. Therefore, non‐local specimens of birds from the lowlands would hint at long‐distance trade. The composition of birds changes through time: species associated with high montane forest and shrubby páramos decrease and species from dry or open montane habitats increase. This trend is dominated by the decrease of Curve‐billed Tinamous Nothoprocta curvirostris (current elevational range 3000–3900 m) and a corresponding increase of specimens of Andean Tinamous Nothoprocta pentlandii (current elevational range 1000–2300 m). The large number of Andean Tinamous is surprising given that presently it occurs no closer than 300 km to the south of the La Chimba site. Overall, 18 of the 43 species of birds identified from La Chimba are likely to be the result of trade. This includes species from the eastern and western lowlands of Ecuador and one possible long‐distance transport from Peru. Prehistoric trade of birds and bird parts was probably common, and prehistoric anthropogenic landscape change and trade in birds should be considered as alternative explanations for species with disjunct populations in and across the Andes.     

A Late Holocene Pollen and Charcoal Record from La Selva Biological Station, Costa Rica

Pollen and charcoal analysis of a 5.9-m-long sediment profile from a swamp on an alluvial terrace on the edge of La Selva biological station, Costa Rica (10°26'23" N, 84°00'24" W, 36 m asl), documents three millennia of human and natural disturbance within a lowland tropical rain forest. The record indicates that the highly diverse rain forest that presently surrounds the Cantarrana swamp regrew following forest clearing and maize agriculture that ended only a few centuries ago. The first maize pollen appears in sediments deposited ∼1070 calendar-year BP. Older sediments below the 'maize zone' contain macroscopic charcoal, abundant microscopic charcoal, and possible pollen indicators of forest clearance, perhaps signaling local cultivation of root crops that left no pollen in the sediments. Interpretation of local archaeology indicates that La Selva reserve may have been most heavily populated during the El Bosque and La Selva regional archaeological phases from 2250–950 yr BP. However, the distribution of maize pollen in the sediments is clear evidence that the reserve was also occupied during the later La Cabaña phase (950–400 yr BP), from which few artifacts have yet surfaced. Natural forest disturbance from treefalls and stream dynamics, and hydrological shifts associated with late-Holocene climate variability, form a backdrop to the human land-use history preserved in the Cantarrana sediment profile.     

Palaeoecological evidence for Holocene vegetation, climate and land-use change in the low Don basin and Kalmuk area, southern Russia

Two¹⁴C-dated pollen profiles from mires in the steppe belt of southern Russia are presented. On the basis of these and data from earlier investigations, the Holocene forest history of the southern part of Russia and Ukraine is reconstructed. The steppe belt is very sensitive to climatic oscillations and, in particular, to changes in evapotranspiration. The most favourable climate occurred between 6000 and 4500 B.P. (6800–5200 cal. B.P.), when forest attained its maximum extent in the steppe belt. The period 4500–3500 B.P. (5200–3800 cal. B.P.) was characterised by drier climate with the most arid phase occurring between 4200–3700 B.P. (4700–4000 cal. B.P.). During arid phases, the area under forest and also peat accumulation rates declined. Subsequently, a number of less pronounced climatic oscillations occurred such as in the period 3400/3300–2800 B.P. (3600/3500–2900 cal. B.P.) when there was a return to more humid conditions. During the last 2500 years, the vegetation cover of the steppe belt in southern Russia and Ukraine took on its present-day aspect. On the one hand, there is close correlation between the Holocene vegetation history of southern Russia and Ukraine and, on the other hand, the steppe belt of Kazakhstan and transgressions in the Caspian sea. Human impact on the natural vegetation became important from the Bronze Age onwards (after 4500 B.P.; 5200 cal. B.P.). Particular attention is given to the history of Scots pine (Pinus sylvestris), which had a much wider distribution in the southern part of eastern Europe in the early Holocene. The reduction in range during recent millennia has come about as a result of the combined effects of both climatic deterioration and increased human impact.     

Environmental changes off North Iceland during the deglaciation and the Holocene: foraminifera, diatoms and stable isotopes

A combined study of foraminifera, diatoms and stable isotopes in marine sediments off North Iceland records major changes in sea surface conditions since about 15 800 cal years (yr) BP. Results are presented from two gravity cores obtained at about 400 m water depth from two separate sedimentary basins on each side of the submarine Kolbeinsey Ridge. The chronology of the sedimentary record is based partly on AMS ¹⁴C dates, partly on the Vedde and the Saksunarvatn tephra markers, as well as the historical Hekla AD 1104 tephra. During the regional deglaciation, the planktonic foraminiferal assemblages are characterised by consistently high percentages of sinistrally coiled Neogloboquadrina pachyderma. However, major environmental variability is reflected by changes in stable isotope values and diatom assemblages. Low δ¹⁸O values indicate a strong freshwater peak as well as possible brine formation by sea-ice freezing during a pre-Bølling interval (Greenland Stadial 2), corresponding to the Heinrich 1 event. The foraminifera suggest a strong concurrent influence of relatively warm and saline Atlantic water, and both the foraminifera and the diatoms suggest mixing of cold and warm water masses. Similar but weaker environmental signals are observed during the Younger Dryas (Greenland Stadial 1) around the level of the Vedde Ash. Each freshwater peak is succeeded by an interval of severe cooling both at the beginning of the Bølling–Allerød Interstadial Complex (Greenland Interstadial 1) and during the Preboreal, presumably associated with the onset of intense deep water formatiom in the Nordic Seas. The Holocene thermal optimum, between 10 200 and about 7000 cal years (yr) BP, is interrupted by a marked cooling of the surface waters around 8200 cal yr BP. This cold event is clearly expressed by a pronounced increase in the percentages of sinistrally coiled N. pachyderma, corresponding to a temperature decrease of about 3°C. A general cooling in the area is indicated after 7000–6000 cal yr BP, both by the diatom data and by the planktonic foraminiferal data. After a severe cooling around 6000 cal yr BP, the planktonic foraminiferal assemblages suggest a warmer interval between 5500 and 4500 cal yr BP. Minor temperature fluctuations are reflected both in the foraminiferal and in the diatom data in the upper part of the record, but the time resolution of the present data is not high enough to pick up details in environmental changes through the late Holocene.     

Foraminiferal response to Holocene environmental changes of a tidal estuary in Victoria, southeastern Australia

The Holocene strata in the Anderson Inlet area in Victoria can be stratigraphically divided into four units, Unit I, Unit II, Unit III, and Unit IV. Unit I and Unit IV lack fossils and were deposited in non-marine, probably fluvial environments. Unit II and Unit III contain abundant foraminifera with molluscs, ostracods and bryozoans. Foraminiferal analysis suggests that Unit III was formed in a partially sheltered marine environment, while the high plankton content and relatively high diversity of benthic species in Unit II indicate that this unit was deposited in an open bay at water depths possibly less than 5 m. The foraminiferal data are integrated with radiocarbon dates to arrive at the following Holocene palaeoenvironmental history in this area: (1) low alluvial plain stage (10,000–7000 yr B.P.); (2) open bay environment stage (7000–5500 yr B.P.); (3) partially sheltered marine environment stage (5500–4500 yr B.P.); (4) alluvial plain and coastal lagoon environment stage (since about 4500 yr B.P.). The foraminiferal fauna show a clear response to these palaeoenvironmental changes. Globigerina bulloides can be used as an indicator for cold water marine environments. The high concentration of this species in these middle Holocene sediments shows a strong cold water influence on the coastal environments which reduced the effect of regional warm currents during this period. The Holocene palaeoenvironmental changes in the area were controlled by the Holocene sea-level fluctuations associated with the deglaciation history during this period. Similar integrated studies of shallow to marginal marine strata in southern Africa, America and New Zealand will lead to a better understanding of Holocene relative sea-level change and the interplay between Holocene cold and warm water regimes in the Southern Hemisphere.     

Late and postglacial vegetation and fire history in Southern Patagonia and Tierra del Fuego

Two 17,000-yr-old peat bog records from low-elevation sites in Tierra del Fuego (Harberton, 54°54′S) and southern Patagonia (Río Rubens, 52°4′48″S) and one c. 14,000 cal yr BP record from the upper treeline in Tierra del Fuego (Paso Garibaldi, 54°43′S) were analyzed for pollen, charcoal, and plant macrofossils to reconstruct changes in regional and local vegetation, fire frequency, and bog hydrology, respectively. Past environmental changes in both lowland records and in the upper treeline record are interpreted in terms of variations in effective moisture. During the late-glacial period, effective moisture changes at both low and high-elevation sites were interpreted from comparable shifts between mesic herb-rich grasslands and arid Empetrum heath or shrub-grassland with abundant disturbance indicators. The late-glacial effective moisture changes were primarily driven by temperature changes. During the early Holocene, expansion of open Nothofagus woodlands in the lowlands in present-day areas of dense forest was related to a marked precipitation increase. However, precipitation must have remained highly variable with century-long periods of increased summer drought, as evidenced by repeated intervals when bogs dried out and fire frequency was high. Up-slope shifts of the Nothofagus forest — Andean tundra ecotone at 11,000 and 9000 cal yr BP also appear to reflect precipitation increases. Precipitation variability, however, must not have affected the upper treeline environments as no fires were recorded and the present-day Nothofagus forest had become established after 9000 cal yr BP. Upper treeline apparently was below present from 8000 to 7000 and 2500 to c. 400 cal yr BP. During those times low-elevation environments did not register change which suggests that the upper treeline may have been affected by lower temperatures. After c. 5000 cal yr BP fires became rare in the lowlands, suggesting a shift to an equable precipitation regime with only minor intervals of summer drought. No simultaneous change was recorded at the upper treeline. Thus, for the late-glacial and early Holocene the upper and lower treeline environments apparently responded similarly to primarily moisture changes. Only during the mid- and late Holocene environmental changes at high and low elevations differed, suggesting responses to different climate signals, precipitation in the lowlands and temperature at high elevation.     

Late quaternary vegetation dynamics and human impact on Alexander Selkirk Island, Chile

Aim To reconstruct the history of vegetation and environments using pollen, charcoal and sediment analysis, and to identify the timing and nature of climate change and human impact on the vegetation of a remote Pacific island. Location Cerro de Los Inocentes, 1000 m above sea level, Alexander Selkirk Island (33°45′S, 80°45′W), Chile. The westernmost island of the Juan Fernandez Archipelago, south‐east Pacific Ocean. Methods A 150‐cm long sediment core comprising 87 cm dark brown peat overlying 63 cm of yellow grey clay was extracted from a shallow depression on the southern slopes of Cerro de Los Inocentes. Pollen, charcoal, sediment and accelerator mass spectrometry radiocarbon analyses were used to construct a record of vegetation change through time. Numerical analysis of multispecies data allowed the classification of fossil assemblages into distinct pollen zones. Results Pollen and spores are preserved throughout the sediment with high concentrations coinciding with the beginning of organic sediment accumulation at around 8000 ¹⁴C yr BP. Prior to 8000 ¹⁴C yr BP, the deposition of clays, presumably from upslope erosion, occurred in a landscape sparsely vegetated by grasses, ferns and Pernettya rigida heath, including several plants that are only found 100–200 m above the site today (Zone CI‐1). After 8000 ¹⁴C yr BP, a P. rigida heath was the dominant vegetation (Zone CI‐2). A shift to a wet heath–shrubland (Zone CI‐3) occurred at 6000 ¹⁴C yr BP and was followed by a transition to a treefern–shrubland mosaic accompanied by periodic burning (Zone CI‐4) after 4500 ¹⁴C yr BP. The impact of human occupation is evident in Zone CI‐5 at 450 ¹⁴C yr BP with the loss of forest species, increased burning and invasion of the exotic plant Rumex. Main conclusions The pollen and charcoal record provides the first evidence of vegetation changes spanning at least the last 8000 ¹⁴C yr BP from the high altitude environment of Alexander Selkirk Island. Prior to 8000 ¹⁴C yr BP, the altitudinal ranges of different plant species may have been suppressed by a cooler and drier climate. Increasing precipitation and temperatures at the end of the last glacial period may have mobilized exposed sediments in a sparsely vegetated upland environment, altering local drainage patterns, eventually leading to slope stabilization and deposition of organic detritus under an increasing density of heath and shrub vegetation. The subalpine heath–shrubland persisted until 4500 ¹⁴C yr BP when first evidence for sustained burning is found in association with the establishment of a more open treefern–shrubland vegetation pattern. In the absence of human occupation at this time, the influence of increased climatic variability associated with more frequent El Niño‐Southern Oscillation events during the mid to late Holocene is considered one of the main driving forces behind increased vegetation disturbance during this period. The record provides evidence that island vegetation patterns have been highly dynamic over millennial to decadal time‐scales and that the flora has persisted through periods of rapid and major climate change. This changed with the discovery of the island by European explorers in the late sixteenth century and the subsequent introduction of goats and exploitation and burning of forests, which resulted in the progressive destruction of native vegetation and the invasion of introduced plants. There is evidence that reduced burning and control of the goat population within the last 50 years has resulted in marginal recovery of some high altitude native plant species.     

Holocene climatic changes in the Western Mediterranean, from south-east France to south-east Spain

Holocene climatic changes along coastal regions from south-east France to south-east Spain were studied using pollen ratios. Comparing modern pollen rain, vegetation and climate along selected transects from the Atlantic Ocean to the Mediterranean, we obtained threshold values of two different ratios corresponding to the different climatic conditions along the transects. These pollen ratios and threshold values were employed to characterize the Holocene climatic changes from nine Mediterranean coastal sites. The results were compared with data from marine and continental pollen sequences distributed in the western Mediterranean basin, and with additional regional data independent of human activity: lake-level fluctuations, alpine glacier advance and retreat chronology, ¹⁴C anomaly and cooling phases in Eastern France and Central Europe. The role of anthropogenic activities and climate on the changes in vegetation is discussed. Six major changes in vegetation cover were identified. They correspond to aridification phases that occurred around 9500–9000 yr BP (10 900–9700 cal BP), 7500–7000 yr BP (8400–7600 cal BP), 4500–4000 yr BP (5300–4200 cal BP), 3700–3300 yr BP (4300–3400 cal BP), 2600–1900 yr BP (2850–1730 cal BP) and 1300–1000 yr BP (1300–750 cal BP). These arid episodes were regional responses to more global climatic changes and determined the changes in the vegetation cover. Humans undoubtedly enhanced the vegetation changes, but none the less had to adapt to these new climatic conditions.