Holocene Vegetation Changes Research Articles

Holocene vegetation change, Aboriginal wetland use and the impact of European settlement on the Fleurieu Peninsula, South Australia

A fossil pollen and charcoal record from a cyperaceous swamp on the Fleurieu Peninsula, South Australia, was investigated to provide a history of pre and post-European settlement vegetation change. It was found that the swamp initiated sometime before 8220 calibrated years BP. High rates of peat development and the expansion of swamp species between 7000 BP and 4500 cal. BP indicated wet conditions at that time. The swamp became drier in the late Holocene and some peat may have been lost through deflation. Macroscopic charcoal and Typha pollen suggested that Aborigines deliberately burned the upland wetlands during the mid to late Holocene. Prior to European settlement climate changes generated community shifts in the terrestrial vegetation. The record revealed a transition from an early Holocene Eucalyptus woodland to an Allocasuarina wet-heath in the humid mid-Holocene, a community type with no modern analogue in the region. In the drier late Holocene, a Eucalyptus-dominated woodland returned. The impacts of European settlement were clearly seen in changes in sedimentation rates and in both terrestrial and wetland flora. Allocasuarina verticillata declined early in the European period and fire tolerant species were promoted, before the almost complete removal of native vegetation through broad scale land clearance and its replacement with nonnative pasture species. Compositional changes to the swamp flora were marked through the European phase with Acacia expanding early in settlement and later being replaced by Leptospermum, in response to changed fire and regional hydrological regimes. The impact of European land use is discussed in relation to Holocene climate-driven vegetation changes and aspects of Aboriginal land use.

Proxy records of late Holocene vegetation and climate changes from Basaha Jheel, Central Ganga Plain - II

Proxy records of late Holocene vegetation and climate changes from Basaha Jheel, Central Ganga Plain - II

Recent vegetation changes in central Queensland, Australia: Evidence from δ13C and 14C analyses of soil organic matter

This study examines whether changes from grassy to woody vegetation coincide with the initiation of European farming practices (last 50–150 years) in central Queensland, using a site where historical records suggest invasion of woody vegetation ( Acacia sp.). Soil samples were taken along a transect, spanning the transition between C4-dominated grassland and C3-dominated woodland. We utilize δ 13C and 14C data of bulk and size-separated soil organic matter (SOM) to infer the time course of changes in vegetation and soil carbon stocks. δ 13C values of bulk SOM indicate a shift from grass (C4)- to tree (C3)-derived carbon in the woodland compared with the grassland. The δ 13C analyses of the size-separates showed that most of the labile, C3-derived carbon was present in the particulate organic carbon (POC) fraction (>53 μm) (down to 30 cm), whereas δ 13C values in the <53 μm fraction showed greater C4 contributions. The δ 13C values of the POC and the <53 μm fractions in the grassland and transition zone were significantly different, inferring a relatively recent change from a C4- to a C3-dominated system (<100 years). This interpretation is supported by 14C data as the 14C activity of both the >200 and 53–200 μm fraction was greater than 108% modern (pMC), indicating that most of the C3-derived POC fractions were formed during the past ∼45 years. This “bomb-derived” carbon (>100 pMC) was present to a depth of 30 cm. Thus, 14C and δ 13C data from the size fractions indicate that much of the vegetation change at this site occurred over the last 50 years. We also found that the thickened site had greater C storage in above-ground biomass and soil carbon stocks compared with the grassy site. Preliminary modelling of changes in carbon stocks, using the Roth-C model, support that the change from grassland to woodland probably occurred <100 years ago.

Development of vegetation in the Central Mojave Desert of California during the late Quaternary

Vegetation analysis of 47 Neotoma (packrat) middens from the core of the central Mojave Desert of California reveal changes in desert plant community composition over the last ca. 24,000 years BP, one of the lowest and most arid locations in North America. Habitat currently dominated by Mojave Desert Larrea tridentata (creosote bush) was occupied prior to ca. 11,500 years BP by Pinus monophylla (piñon), Juniperus osteosperma (Utah juniper), Purshia mexicana (bitterbush), Cercocarpus ledifolius (mountain mahogany), and Prunus fasciculata (desert almond) woodland above 1000 m. P. monophylla– Juniperus woodland was widespread over the southern and central Mojave Desert. However, less than 150 km north of the central Mojave, J. osteosperma steppe dominated the landscape. Paleoecologic records spanning latitude 35°N ca. 37°N document a biogeographic boundary between milder, moister environments to the south and the colder, drier environments to the north. At elevations <1000 m desert scrub species of Lycium cooperi (wolfberry), Salvia mojavensis (Mojave sage) and the mesophytic Prosopis juliflora (mesquite) occurred near the shore of pluvial Lake Mojave from ca. 8810 to 8430 years BP. Larrea is not recorded on the xeric carbonate substrates (605 m) until ca. 6990 years BP, then took over 2000 years to dominate the regional landscape. Modern vegetation associates such as Thamnosma montana (desert rue) and Atriplex confertifolia (shadscale) were established by ca. 4500 years BP. Late Holocene vegetation changes document Neoglacial cooling and wetter conditions than today between ca. 3490 and 2640 years BP, paralleling the regional pluvial lake highstands and marsh deposit records. Decreases of mesophytic Mojave Desert associates in the Granite Mountains suggest climates similar to today's aridity between ca. 1970 and 1440 years BP. Mesophytic species increase in middens dating between ca. 1390 and 700 years BP at higher elevation sites; during the same time Prosopis occurs at lower elevation sites.

Lateglacial and Holocene vegetation change on the Isle of Skye: new data from three coastal locations

Detailed lithostratigraphical and biostratigraphical studies from three contrasting coastal sites on the Isle of Skye were undertaken to investigate spatial variations in vegetation development on the island since the Lateglacial. The pollen profiles were then compared with the published pollen data for Skye. The new data reveal broadly similar trends for the sites studied and show that these correspond well to the previously established chronology. A date of ca. 10110 radiocarbon years B.P. has been obtained for the rational rise in Corylus, a date of ca. 8850 uncal B.P. for the appearance of Ulmus and a date of ca. 6600 uncal B.P. for the rise in Alnus. However, significant variations were evident and these were due to (a) coastal proximity, which directly affects vegetation composition through the low but persistent presence of Armeria and Chenopodiaceae, (b) altitude, which determines the effect of rising groundwater that may be related to relative sea level rise, and (c) aspect and position in relation to central Cuillin mountain range, through exposure to SW winds that restrict the development of thermophilous woodland and encourage the acidification of heathlands and development of herb-rich grasslands from ca. 4000 B.P.. This study reveals that the range of variation caused by these local factors is as great as the variation found throughout the island. This has negative implications for the reconstruction of regional patterns of vegetation change but highlights the range of local habitats and wild resources available to early inhabitants of the island.

Holocene vegetation change and the mammal faunas of South America and Africa

AbstractAim Although sharing many similarities in their vegetation types, South America and Africa harbour very dissimilar recent mammal faunas, not only taxonomically but also in terms of several faunistic patterns. However late Pleistocene and mid‐Holocene faunas, albeit taxonomically distinct, presented many convergent attributes. Here we propose that the effects of the Holocene climatic change on vegetation physiognomy has played a crucial role in shaping the extant mammalian faunistic patterns.Location South America and Africa from the late Pleistocene to the present.Methods Data presented here have been compiled from many distinct sources, including palaeontological and neontological mammalian studies, palaeoclimatology, palynology, and publications on vegetation ecology. Data on Pleistocene, Holocene and extant mammal faunas of South America and Africa allowed us to establish a number of similar and dissimilar faunistic patterns between the two continents across time. We then considered what changes in vegetation physiognomy would have occurred under the late Pleistocene last glacial maximum (LGM) and the Holocene climatic optimum (HCO) climatic regimes. We have ordained these proposed vegetation changes along rough physiognomic seral stages according to assumptions based on current botanical research. Finally, we have associated our hypothesized vegetation changes in South America and Africa with mammalian faunistic patterns, establishing a putative causal relationship between them.Results The extant mammal faunas of South America and Africa differ widely in taxonomical composition; the number of medium and large species they possess; behavioural and ecological characteristics related to herbivore herding, migration and predation; and biogeographical patterns. All such distinctions are mostly related to the open formation faunas, and have been completely established around the mid‐Holocene. Considering that the mid‐Holocene was a time of greater humidity than the late Pleistocene, vegetation cover in South America and Africa would have been dominated by forest or closed vegetation landscapes, at least for most of their lower altitude tropical regions. We attribute the loss of larger‐sized mammal lineages in South America to the decrease of open vegetation area, and their survival in Africa to the existence of vast savannas in formerly steppic or desertic areas in subtropical Africa, north and south of the equator. Alternative explanations, mostly dealing with the disappearance of South American megamammals, are then reviewed and criticized.Main conclusions The reduction of open formation areas during the HCO in South America and Africa explains most of the present distinct faunistic patterns between the two continents. While South America would have lost most of its open formations within the 30° latitudinal belt, Africa would have kept large areas suitable to the open formation mammalian fauna in areas presently occupied by desert and semi‐arid vegetation. Thus, the same general climatic events that affected South America in the late Pleistocene and Holocene also affected Africa, leading to our present day faunistic dissimilarities by maintaining the African mammalian communities almost unchanged while dramatically altering those of South America.

Holocene vegetation changes in the northwestern Mediterranean: new palaeoecological data from charcoal analysis and quantitative eco-anatomy

The stratigraphic sequence of Montou (Eastern Pyrenees, France) covers a period from the middle Neolithic to the late Bronze Age. Environmental changes are noticed since the middle Neolithic, when the decline of the deciduous oak favours, in the long term, the evergreen oaks. The Chalcolithic period witnesses the arrival and spread of mesomediterranean and thermomediterranean plant formations. This evolution may result from increasing anthropogenic pressure as shown by the maintenance of a garrigue vegetation during the Bronze Age. The association charcoal analysis/quantitative anatomy offers new perspectives concerning vegetation changes. Both approaches record the existence of mesomediterranean bioclimatic conditions during the middle Neolithic; thermomediterranean affinities are recorded first, by charcoal analysis, during the early Bronze Age, and by eco-anatomy during the transition from the middle to the late Bronze Age. Quantitative anatomy also pinpoints (1) the existence of two humid phases, (2) an increase in mean annual temperature, and (3) the exploitation and management of the olive tree since the early Bronze Age.

Late Glacial and Holocene vegetational changes on the Ulagan high-mountain plateau, Altai Mountains, southern Siberia

Three well-dated pollen diagrams from 1985 m, 2050 m, and at the tree line at 2150 m asl show the vegetational succession in the central Altai Mountains since 16 cal ka BP. Pioneer vegetation after deglaciation was recorded first at the lowest site. Subsequently, dense dry steppe vegetation developed coincident with the change from silt to organic sediments at the two lower sites, but silt lasted longer at the highest site, indicating the persistence of bare ground there. Forests of Pinus sibirica, Pinus sylvestris, Picea obovata, Larix sibirica, Abies sibirica, and Betula pendula started to develop about 12 cal ka BP with the change to a warmer and wetter climate at the beginning of the Holocene. Results indicate that the timberline did not rise above the highest site. Mesophilous dark-coniferous forests were fully developed by 9.5 cal ka BP. The role of Abies and Picea decreased by about 7.5 cal ka BP suggesting cooler climate, after which the forests changed little until today. The vegetational development in this portion of the central Altai Mountains is compatible with that described in neighbouring areas of the Altai, southern Siberia, Mongolia, and Kazakhstan.

The Lateglacial and Holocene environmental history of the Ioannina basin, north-west Greece

This study centres on palaeoenvironmental analysis of the upper part of a long core from the partially drained, tectonic Ioannina basin, north-west Greece. The data span the Lateglacial and Holocene and comprise pollen, mollusc, magnetic susceptibility, loss-on-ignition and particle size analyses. These augment previously published ostracod and stable isotope data from the same sediment sequence. The age model for the sequence is based on 19 AMS dates, five of which were obtained using a novel procedure for the separation of microcharcoal from sediment. The pollen data suggest that although temperate woodland expanded at the beginning of the Lateglacial, only limited woodland contraction occurred during the Younger Dryas chronozone, despite strong evidence for a sharp drop in sea surface temperature in the neighbouring Adriatic at this time. In contrast, large-scale vegetational and sedimentological changes occur in concert during the Holocene, some of which may be ascribed to human impact. Comparison with other records from the Ioannina basin suggests that previous, more littoral pollen sequences did not constitute a wholly representative record of Lateglacial and Holocene vegetational change.

Fifty-thousand-year vegetation and climate history of Noel Kempff Mercado National Park, Bolivian Amazon

Pollen and charcoal records from two large, shallow lakes reveal that throughout most of the past 50,000 yr Noel Kempff Mercado National Park, in northeastern lowland Bolivia (southwestern Amazon Basin), was predominantly covered by savannas and seasonally dry semideciduous forests. Lowered atmospheric CO 2 concentrations, in combination with a longer dry season, caused expansion of dry forests and savannas during the last glacial period, especially at the last glacial maximum. These ecosystems persisted until the mid-Holocene, although they underwent significant species reassortment. Forest communities containing a mixture of evergreen and semideciduous species began to expand between 6000 and 3000 14C yr B.P. Humid evergreen rain forests expanded to cover most of the area within the past 2000 14C yr B.P., coincident with a reduction in fire frequencies. Comparisons between modern pollen spectra and vegetation reveal that the Moraceae-dominated rain forest pollen spectra likely have a regional source area at least 2–3 km beyond the lake shore, whereas the grass- and sedge-dominated savanna pollen spectra likely have a predominantly local source area. The Holocene vegetation changes are consistent with independent paleoprecipitation records from the Bolivian Altiplano and paleovegetation records from other parts of southwestern Amazonia. The progressive expansion in rain forests through the Holocene can be largely attributed to enhanced convective activity over Amazonia, due to greater seasonality of insolation in the Southern Hemisphere tropics driven by the precession cycle according to the Milankovitch Astronomical Theory.

Input rates, decay losses and accumulation rates of carbon in bogs during the last millennium: internal processes and environmental changes

In peatlands the balance between litter input and decay loss in the oxic acrotelm determines the rate of carbon input to the anoxic catotelm with carbon lost at very slow rate. In the acrotelm the C/N-quotient decreases with depth and indicates the loss of carbon from the acrotelm. On one boreo-nemoral and three subalpine ombrotrophic bogs in Sweden the carbon losses in the acrotelm plus the apparent carbon-accumu lation rates in the catotelm for the last millennium revealed a constant carbon-sequestering rate up to the end of the nineteenth century equalling that in recent Sphagnum-dominated communities. On the boreo-nemoral bog the carbon-accumulation rate in the catotelm decreased by 50% over the same period while it remained constant on the subalpine bogs. A catotelm with permafrost may have provided more constant conditions for the carbon accumulation than a rising water level creating anoxic conditions. Due to vegetation changes, the recent carbon sequestering in the peat-forming communities is lower than previously and only just enough to compensate for the integrated losses. It is argued that because of internal processes the bogs up to the end of the nineteenth century had obtained or were approaching a steady-state with regard to the carbon input to the catotelm and the supply of mineral nutrients. In contrast, an increased climatic humidity around 1000 cal. BP resulted in high carbon-accumulation rates in the boreo-nemoral bog. Climate could have triggered the recent vegetation changes, but an increased nitrogen deposition is also a probable reason.

Macroalgal Population Explosion And Water Purification - Survey, Assessment And Prognosis

Algal resources, their use and potential, have been investigated, but recent changes in marine benthic vegetation and the effects of eutrophication have also been using - the subject of investigation and concern. Solutions to these problems could lead to using, in some sites and under specific conditions, blooms in the prevention of further deterioration of coastal water quality. In addition, the urgent need to protect marine ecosystems may lead to the use of marine macrophytes as agents for tertiary waste-water treatment. Seaweeds are well suited for nitrogen-rich domestic and urban sewage purification, even for agricultural, fishpond and industrial polluted waters. A major impediment in implementing the encouraging results remains the economic benefit derived from such operations. In general, the operations remain, if not cost-prohibitive, then commercially non-profitable. Environmental and sustainability concerns may, in a not too distant future, override the lack of financial benefit.

Landscape patterns of vegetation change indicated by soil carbon isotope composition

Vegetation change, particularly from the grass to shrub life form, is a critical issue on the world's semiarid rangelands. Stable carbon isotope (δ 13C) values and associated radiocarbon ages from soil organic matter (SOM) were used to evaluate vegetation change across five landscape positions at a small enclosed basin in southeastern Arizona. Light and dense SOM fractions were separated to distinguish recent vegetation changes. The direction and timing of vegetation change differed with landscape position along a gentle elevation gradient from the basin outlet to a nearby volcanic ridge top. C 4 perennial grasses have dominated the basin outlet, center, and toe slope landscape positions since at least 5000–6000 years BP, except for the dominance of C 3 plants at the bottom of the outlet excavation at 5000 years BP. This isotopic change is associated with rounded cobbles that may have been a stream channel, suggesting the presence of C 3 herbaceous or woody riparian vegetation. On mid-slope and ridge top landscape positions, where semidesert shrubs now dominate, the proportion of plants with C 4 metabolism calculated from mass balance mixing formulas decreased from approximately 60% as recently as 400 years BP to only 1.5% observed today. The light SOM fraction from mid-slope and ridge top surface soil horizons was approximately 30% C 4 and had a post-bomb date, suggesting that the conversion from grass to shrub occurred over the last several decades.

Recent changes in riparian vegetation: possible consequences on dead wood processing along rivers

AbstractLittle is known about changes in the composition of dead wood jams along rivers and the possible consequences of any such changes on the river ecosystem. Although tree zonation along the upstream‐to‐downstream continuum is weak and highly variable from a system to another, a clear transition appears in the piedmont zone, which is reflected by transitions in dead wood sources as well as for dead wood transport, storage and decomposition processes. In this paper, we focus on large lowland rivers of southwestern France, where riparian vegetation is increasingly fragmented, reduced in area and/or is entirely replaced by planted forests (poplar plantations). The amount and the potential role of dead wood is practically unknown in these rivers. One reason is that French legislation obliges landowners and public service managers to remove all material from the stream in order to maintain unobstructed river flows. The other reason is that unlike pristine streams in northern regions, these rivers have been regulated for several decades (Adour River) or even for several centuries (Garonne River). The vegetation component of the managed riparian landscape has changed in particular as a result of i) a decrease in stream dynamics, ii) the replacement of natural forests by planted ones, and iii) the invasion of natural communities by introduced woody species.The possible consequences of biological invasions on the role of dead wood jams are discussed in light of: i) a local study of wood jams along a moderately modified system; ii) changes observed in the composition of trees along the Adour River over the past 10 years; iii) a regional case study involving two chosen species. Whereas white willow populations are declining along streams in southwestern France, the box‐elder, introduced from the United States, has spread extensively in the last two decades. Statistical models would suggest that competitive pressures are limited between these two species, boxelder is expected to replace white willow in the near future as a consequence of an increase in river regulation and global warming. This can be expected to have important consequences on dead wood dynamics, and on the management of woody debris, especially since trends indicate a replacement of softwood species by hardwood species. Copyright © 2003 John Wiley &amp; Sons, Ltd.

A Preliminary Investigation on the Holocene Vegetation Changes From Pollen Analysis in the Gaoximage Section, Hunshandak Sandy Land

A Preliminary Investigation on the Holocene Vegetation Changes From Pollen Analysis in the Gaoximage Section, Hunshandak Sandy Land

Late‐glacial and early Holocene changes in vegetation and lake‐level at Hauterive/Rouges‐Terres, Lake Neuchâtel (Switzerland)

AbstractPalynological and sedimentological analyses of a sedimentary sequence sampled at Hauterive/Rouges‐Terres, Lake Neuchâtel (Switzerland) provide documentation of changes in vegetation and lake‐level during the Bølling, Younger Dryas and Preboreal pollen zones, and have allowed a comparison with sequences covering the same period from other sites located in the western part of the Swiss Plateau. The Juniperus–Hippophaë zone (regional pollen assemblage zone (RPAZ) CHb‐2, first part of the Bølling, ca. 14 650–14 450 cal. yr BP) was characterised by a generally low lake‐level. A weak rise occurred during this zone. The Juniperus–Hippophaë to Betula zone transition coincided with a lake‐level lowering, interrupted by a short‐lived but marked phase of higher lake‐level recorded at the neighbouring site of Hauterive‐Champréveyres, but not present at Hauterive/Rouges‐Terres owing to an erosion surface. Shortly after the beginning of the Betula zone (RPAZ CHb‐3, second part of the Bølling, ca 14 450–14 000 cal. yr BP), a marked rise in lake‐level occurred. It was composed of two successive periods of higher level, coinciding with high values of Betula, separated by a short episode of relatively lower lake‐level associated with raised values in Artemisia and other non‐arboreal pollen. The last part of RPAZ CHb‐3 saw a fall in lake‐level. The lower lake‐levels during RPAZ CHb‐2 to early RPAZ CHb‐3 can be correlated with the abrupt warming at the beginning of the Greenland Interstadial (GI) 1e thermal maximum. The successive episodes of higher lake‐level punctuating the GI 1e might be linked to the so‐called Intra‐Bølling Cold Oscillations identified from several palaeoclimatic records in the North Atlantic area, and also documented in oxygen‐isotope data sets from Swiss Plateau lakes. The Hauterive/Rouges‐Terres lake‐level record provides evidence for marked climatic drying through the second part of the Younger Dryas event (GS1), during the GS1–Preboreal (RPAZ CHb‐4b–4c) transition (except for a rise at ca. 11 450–11 400 cal. yr BP), and at the RPAZ CHb‐4c–5 (Preboreal–Boreal) transition, following the Preboreal Oscillation (after 11 150 cal. yr BP). The Preboreal Oscillation coincided with higher lake‐levels, its end being followed by a rapid expansion of Corylus, Quercus, Ulmus and Tilia. The Hauterive/Rouges‐Terres lake‐level record suggests that radiocarbon plateau at 12 600, 10 000 and 9500 14C yr BP corresponded to periods of generally lower lake‐level. This suggests that an increase in solar activity may have contributed to both climatic dryness and a decrease in atmospheric radiocarbon content. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Holocene Vegetation and Climate History of the Northern Bighorn Basin, Southern Montana

Records of Holocene vegetation and climate change at low elevations (<2000 m) are rare in the central Rocky Mountain region. We developed a record of Holocene vegetation and climate change from 55 14C-dated woodrat middens at two low-elevation sites (1275 to 1590 m), currently vegetated by Juniperus osteosperma woodlands, in the northern Bighorn Basin. Macrofossil and pollen analyses show that the early Holocene was cooler than today, with warming and drying in the middle Holocene. During the Holocene, boreal ( Juniperus communis, J. horizontalis) and montane species ( J. scopulorum) were replaced by a Great Basin species ( J. osteosperma). J. osteosperma colonized the east side of the Pryor Mountains 4700 14C yr B.P. Downward movement of lower treeline indicates wetter conditions between 4400 and 2700 14C yr B.P. Increased aridity after 2700 14C yr B.P. initiated expansion of J. osteosperma from the east to west side of the Pryor Mountains.

Late Holocene Vegetation Change in the Sierra Madre Oriental of Central Mexico

Past vegetation and climate changes reconstructed from a sediment core from Laguna Atezca, Molango, Mexico, provide new insights into the environmental and cultural histories of the Sierra Madre Oriental during the last 1700 yr. Pollen, microscopic charcoal, sediment chemistry, loss on ignition, and magnetic susceptibility indicate that three phases of human occupation, deforestation, and erosion (ca. A.D. 280–890, ca. A.D. 1030–1420, and ca. A.D. 1680–present) alternate with two phases of abandonment (ca. A.D. 890–1030 and ca. A.D. 1420–1680). Forest composition of the two abandonment phases differed, with cloud forest taxa ( Liquidambar, Ostrya/Carpinus, Ulmus, etc.) dominating the pollen record during the first phase, and Quercus and Pinus pollen characterizing phase two. These differences may reflect a climate change in which the second phase was drier than the first; Alternatively, the increase in Pinus and Quercus may have been caused by a human-induced decline in soil fertility. The Laguna Atezca record also differs from several other Mesoamerican paleoenvironmental records in that it shows no evidence of drought at the end of the Classic Period, ca. A.D. 900.

Holocene vegetation and climate change in southern New Zealand: linkages between forest composition and quantitative surface moisture reconstructions from an ombrogenous bog

AbstractThis paper presents a Holocene pollen record from an ombrotrophic bog in Southland, New Zealand, together with multiproxy data (testate amoebae, peat humification and plant macrofossils) from the same core to establish an independent semiquantitative record of peatland surface moisture. Linkages between reconstructed peatland surface moisture and regional forest composition are investigated using redundancy analysis of the forest pollen data constrained with predicted bog water‐table depths. Over 32% of the pollen data variance can be explained by surface moisture changes in the bog, suggesting a common cause of water‐table and regional vegetation change. Water tables were higher during the early to mid‐Holocene when the forest was dominated by podocarp taxa. Water tables lowered after about 3300 cal. yr BP coevally with the expansion of Nothofagus species, culminating with the dominance of Nothofagus subgenus Fuscospora in the past 1200 cal. yr BP. This is in apparent opposition to the warm/dry to cool/wet trend suggested by subjective interpretation of pollen data alone, from this and other studies. We suggest that during the late Holocene, drier summers associated with shifts in solar insolation caused reduced surface wetness and summer humidity, which together with a trend to cooler winters, apparently favoured the regeneration of Nothofagus species. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Vegetation and climate during the Holocene in Southwest Patagonia, Argentina

Pollen analysis from archaeological sequences in the Lago Argentino area (Southwest Santa Cruz province, Argentina) are used to infer vegetation and climatic changes during the Holocene. These sequences are located in present-day grass and shrub steppes and in Andean desert. Comparison with modern pollen data and other fossil pollen sequences provides a regional analysis of Holocene vegetational changes and contributes to the understanding of the regional paleoclimatic history. The fossil records indicate that a grass steppe developed in the area at the beginning of the Holocene. According to the pollen spectra, a change to shrub steppe took place between 8500 and 3500 yr BP, suggesting drier conditions. The presence of grass steppe may relate to greater availability of moisture and decrease in temperature in the south of Lago Argentino from 3500 yr BP, and in the northern and eastern portions of the area from ca. 1000 yr BP onwards. In the high Andean zone a herbaceous-shrub steppe with Empetrum developed between 4500 and 3600 yr BP which indicates conditions colder than today. Towards 3600 yr BP an increase in Asteraceae, dominant up to 200 yr BP, indicates less availability of moisture. During the last 200 yr expansion of shrub steppe and decrease of the forest are documented. This period coincides with the increased European settlement of the region. The paleoenvironmental interpretation is related to human populations living in Southwest Patagonia since early Holocene times.