The late Quaternary vegetation history of the south‐central highlands of Victoria,Australia. II. Sites below 900 m

The late Quaternary vegetation communities of the south‐central highlands of Victoria are constructed from analyses of pollen and charcoal, and macroscopic plant remains preserved in Sphagnum bogs. The sites, located in eucalypt forest or woodland, form an altitudinal sequence with the component Eucalyptus species varying with altitude and with small pockets of Nothofagus cunninghamii (Hook.) Oerst. in close proximity to the higher sites. The record from the sites above 900 m covers the last 32 000 years, and the record from the lower sites extends from at least 12 000 BP . Around 32 000 BP the region was predominantly covered by a mosaic of alpine feldmark and herbfield, with small patches of Eucalyptus and Nothofagus woodland close to sea level when summer temperatures were probably 5°C lower than present. Lowest values, probably 7°–8°C below present, occurred between 19 800 and 16 900 BP , when alpine communities were most widespread and much of the Central Highlands was treeless. Around 12 000 BP alpine taxa disappeared or were greatly reduced, first at the lower sites. There was an associated rise in the treeline with the movement upslope of Nothofagus and eucalypt forest as a result of a general increase in temperature and probably effective precipitation. By 6000 BP wet eucalypt forest and Nothofagus reached their maximum postglacial extent at all sites, possibly related to a further increase in temperature, at least 2°C lower than present, and higher effective precipitation. A continuing increase in temperature, or an increase in continentality, and a decrease in effective precipitation led to increased fire hazard and retraction of rainforest and wet sclerophyll or tall open forest toward present‐day values. Nothofagus disappeared from the sites below 900 m. The activities of humans pose further threats to remaining forest communities. The record of vegetation and environmental change derived from the local and regional picture from eight sites reinforces and complements that from the individual sites. For example, combining the records overcomes to some extent taphonomic problems such as the effect of streams that flow close to all sites, and other limitations including problems of dating, poor preservation and variable sedimentation rates.     

Groundwater rise,soil salinization and the decline of Casuarina in southeastern Australia during the late Quaternary

Abstract The decline in interglacial importance of Casuarina over the late Quaternary across southeastern Australia is documented. Three previously proposed causes for the decline (change in fire regime, change to a wetter climate and competitive exclusion by eucalypts) are shown to be inadequate for explaining the majority of cases. Re-examination of the evidence shows the decline at most sites occurred synchronously with a rise in groundwater or soil salinization, or both. From a review of biological literature, it is established that Casuarina stricta, the main species considered to have been affected by the decline, is likely to be disadvantaged by high water tables and saline soils. A link is demonstrated between groundwater salinity and the nodulation status of Casuarina in Victoria. It is concluded that the late Quaternary Casuarina decline was caused by a combination of rising groundwater levels and soil salinization. Soil salinization and groundwater level must therefore be considered as major factors determining vegetation patterns in southeastern Australia through the Quaternary up to the present day.     

Vegetation history from archaeological charcoals in central Australia: The late Quaternary record from Puritjarra rock shelter

Archaeological charcoals from Puritjarra rock shelter provide the first direct information about the vegetation of central Australia during the late Pleistocene and early Holocene. During the late Pleistocene there appears to have been a more open vegetation than today with fewer trees and shrubs, though with many of the taxa that are important in the modern central Australian flora. The persistence of species such as Acacia macdonnelliensis, Callitris glaucophylla and Eucalyptus opaca throughout the time of the last glacial maximum and the presence of appreciable quantities of wood charcoal in the archaeological deposits at this time indicate that the region was not a tree-less steppe even during full glacial aridity. From 13,000 B.P. onwards, acacias are strongly represented in the charcoal assemblage both quantitatively and in terms of the number of species present. Acacia aneura is for the first time a major component of the assemblage indicating that it had by this time become a significant element of the local vegetation. These changes coincide with evidence elsewhere in the Australian arid zone for the onset of wetter conditions in the early Holocene.     

A late Quaternary marine palynological record (oxygen isotope stages 1 to 7) for the humid tropics of northeastern Australia based on ODP Site 820

A late Quaternary marine palynological record from the Ocean Drilling Program (ODP) site 820, adjacent to the humid tropics region of northeastern Australia, has demonstrated marked variation in orbital scale cyclicity, and also trends associated with both climate and human impact. However, some uncertainties in interpretation have resulted from concerns about the records chronology and continuity. Here we present, for the first time, the complete palynological data from detailed analysis of the top 67 m of sediment and examine it in relation to the marine isotope sequence from the core. It is proposed that the record is relatively continuous through the last 250,000 years although the latter part of oxygen isotope stage (OIS) 5, as well OIS 4 may be missing. Despite the variation on orbital scales, most palynological changes are not in phase with those from the marine isotope record suggesting a lack of direct Milankovitch forcing on vegetation. This lack of correspondence combined with major trends towards more open and sclerophyllous vegetation in association with increased burning supports a previous proposal that major control is being exercised by El Niño-Southern Oscillation variability whose influence may have been initiated by changes in oceanic circulation in the region within the mid Pleistocene. The lack of impact on the distribution of complex rainforest suggests that increased climate variability did not involve an overall decrease in total precipitation.     

Late Quaternary vegetation and climatic history of eastern Nepal

The late Quaternary vegetation and climatic history at high altitude in eastern Nepal was studied through stratigraphy, radiocarbon dating and pollen analysis. The Thulo Pokhari lake (27°41′ N, 87°43′ E, ca. 3980 m a.s.l.) is just above the subalpine Abies spectabilis–Betula utilis forest zone and surrounded by Rhododendron scrub. The climate in the studied area is very humid under the influence of the monsoon. Silty sediments suggesting lake conditions prevailed at the lower part of the sediment samples, whereas the upper part consisted mainly of herbaceous peat indicating a mire condition. The pollen record extends back to ca. 11000 yr bp . Although the absence of major changes between the pollen assemblages of the Pleistocene and those in the Holocene was attributed to the situation of the sampling plot above the forest limit, the results suggest the following history. (1) The abundance of Pinus pollen around 11000 yr bp represents expansion of the area unoccupied by late successional trees and/or a drier condition. Significant occurrence of Picea pollen is noteworthy, since this genus is absent in eastern Nepal at present in spite of its wide distribution throughout the neighbouring areas of the Himalayas. (2) The increase in abundance of Quercus pollen and the decline in Pinus pollen in the latest Pleistocene represent climatic amelioration favourable to late successional mesophytes. (3) The climate was most moist and mild in the SP-III, although the absolute age of the pollen zone is not distinct. The percentages of broadleaved trees such as Alnus, Betula, Carpinus and Corylus were increased at the expense of Quercus and coniferous pollen types. Sedimentation was interrupted by lake level decline and/or glacial advance during the period from ca. 11000–1600 yr bp . (4) The increase in abundance of coniferous pollen types such as Pinus, Abies and Tsuga indicates that the climate became drier and cooler, and the present subalpine forest zone composed of A. spectabilis, T. dumosa and Betula utilis was established around 1600 yr bp . The formation of bog or alpine meadow vegetation during the period was shown by the ¹⁴C dates of the peat and the increase in Rosaceae and herbaceous pollen. (5) The increase in abundance of Ericaceae and Alnus pollen in the SP-V indicates that the present alpine Rhododendron scrub zone has been established since ca. 940 yr bp as a result of human influence on the original vegetation. This interpretation is supported by the decline in the proportion of arboreal pollen. Since the age of the initiation of human influence varies with the altitude and region, further study will be necessary to determine the accurate age.     

Late Quaternary vegetation history of the Mexican highland

Results of pollenanalytical investigations in the Highlands of Mexico (area of Puebla — Tlaxcala) are presented together with a survey of the last 35 000 years of vegetation history. After 3 pine periods from 35 000 to about 7 000–8 000 B. P., according to high and late Pleistocene condition, the Holocene vegetation history becomes more diversified: periods of alder, pine, fir and mixed oak forests alternate and end in a period of cultivated landscape.     

Humptulips revisited: a revised interpretation of Quaternary vegetation and climate of western Washington, USA

New pollen data from a 770-cm core of a mire at Humptulips on the southwestern Olympic Peninsula (47°17′00″N, 123°54′40″W) and from a nearby deposit regarded as interglacial in age on the West Fork of the Humptulips River provide evidence for a reinterpretation of previous accounts of the Quaternary vegetation and climate. Using a new age model, the highly variable record at Humptulips is here correlated with marine oxygen-isotope stages (OIS) 1–5a. Vegetation during OIS 5a was pine-dominated, mixed woodland and tundra. In OIS 4, 3, and 2, oscillations in pollen assemblages imply repeated intervals of mountain hemlock parkland and tundra. Pine, as an indicator of openness, is also abundant in these stages. Interstadial fluctuations in OIS 3 reflect episodes of lowland western hemlock communities. The earliest of the episodes is of infinite radiocarbon age and the latest dates to approximately 30,000 ¹⁴C yr B.P. Parkland in OIS 2, occurring after 24,600 until at least 18,440 ¹⁴C yr B.P., was replaced by transitional pine–alder in OIS 1 (Holocene), which, unlike any of the earlier stages, conveys the development of modern lowland forest dominated by western hemlock. Pollen assemblages over the length of record imply that temperature and humidity at no time were as high as at present; only in OIS 3 do conditions approach those occurring in OIS 1. During OIS 2, 3, and 4, when tree line apparently stood at the location of the site, climate was colder and drier. Temperatures were depressed an estimated ≥5°C with precipitation close to 1000 mm compared with 2000–3000 mm at present. Atmospheric circulation during OIS 2 appears to have been much controlled by the location of the Laurentide ice sheet in the continental interior, whereas under the current climatic regime beginning in the early Holocene, westerly air flow has dominated, regulated by interplay between the North Pacific high in summer and the wintertime Aleutian low.     

A palynological investigation of Holocene vegetation change in Torres Strait, seasonal tropics of northern Australia

The islands of Torres Strait occupy a shallow area of submerged continental shelf narrowly separating Cape York Peninsula, Australia, from New Guinea. The human history of Torres Strait is unique with respect to mainland northern Australia. Island vegetation, however, exhibits a strong affinity with the environments of the western lowlands regions of Cape York Peninsula and with the vegetation of seasonal tropical Australia in general. Cape York Peninsula is both climatically and biologically diverse, yet few pollen studies have been carried out in its seasonally tropical environments. A summary presentation of palynological results, tracing the nature of vegetation change in Torres Strait, offers a possible framework for vegetation changes in similar environments on mainland Australia and also provides an opportunity to explore the relationship between Quaternary change in humid-tropical Australian environments and their seasonal-tropical counterparts.Six pollen records from Torres Strait provide evidence of vegetation change and fire history over approximately the last 8000 years. Near-shore sediments reveal a Holocene succession in vegetation incorporating lower-tidal mangrove, upper-tidal mangrove, saltmarsh and freshwater swamp communities. Extensive stable mangrove communities dominated coastal Torres Strait between approximately 6000 and 3000 radiocarbon years before present (yr BP). Inland, the strongest Myrtaceae-forest and rainforest representation occurs around the mid-Holocene only to be replaced by open sclerophyll woodlands, as tree density and diversity decline in the last 3000 years. The development of continuous island freshwater swamp conditions, at the coast and inland, is similarly restricted to the late Holocene (c. 2600 yr BP) and fire, as a prominent feature in the Torres Strait environment, is also a relatively recent phenomenon. Comparisons with regional mainland Australian palynological records reveal a degree of consistency in results from Torres Strait suggesting a similarity in late Quaternary trends through Australian humid and seasonally tropical environments. A number of differences, however, are also apparent, highlighting a degree of diversity which warrants further attention.     

Late Quaternary paleoecology from fossil beetle communities in the Awatere Valley, South Island, New Zealand

Aim The research aim is to reconstruct last glacial maximum (LGM) and Holocene vegetation history and ecology from fossil beetle assemblages. Location The LGM and Holocene sites are located in the Awatere Valley, which lies in the tectonically active Marlborough Region in the north east of the South Island of New Zealand. Methods Beetle fossils were extracted from silty organic sediment using the standard kerosene flotation method. Fossils were identified by comparisons made to modern species based on morphology and surface features. The ecology and distribution of modern analogues are extrapolated to reconstruct the fossil environment. Results One hundred and forty‐five beetle species belonging to 33 families were identified. The LGM fossil fauna showed the local vegetation was characterized by a forest patch surrounded by an open tussock/grassland landscape. This Nothofagus (southern beech) forest persisted at the site until mid‐Holocene when it was replaced by a podocarp forest that contained high beetle diversity. Herbivores dominate in the early stage of this zone, indicating a relatively new forest environment. Later in the Holocene, the fauna is dominated by detritivores indicating an older more established forest. The late Holocene is characterized by low diversity and the absence of forest species. This fauna indicates that by 500 years ago, the forest was absent and is associated with an almost compete loss of beetle biodiversity. Main conclusions The fossil beetles provide a unique perspective into the past environment in the Awatere Valley on a local scale. The reconstruction supports regional pollen interpretations of Holocene vegetation by identifying a specific forest patch. Fossil beetles are thus a valuable local proxy for vegetation reconstructions.     

Influence of rainfall seasonality on African lowland vegetation during the Late Quaternary: pollen evidence from Lake Masoko, Tanzania

Aim  To determine if changes in the key bioclimatic parameters associated with rainfall seasonality can be quantified from fossil sequences and to distinguish them from changes in the total annual rainfall.
Location  Lake Masoko, southern Tanzania (9°20' S, 33°45' E, 840 m a.s.l.).
Methods  Fossil pollen was extracted from a long and well-dated sedimentary sequence spanning the period 45,000–4400 cal. yr bp . The modern habitat, geographical distribution and climatic range (mean annual rainfall and temperature, and length of the dry season) of selected East African plants were used to infer past rainfall attributes for the most characteristic fossil pollen taxa identified from the sediments of Lake Masoko.
Results  In the Masoko pollen sequence it has been possible to identify changes in the length/severity of the dry season during the last 45,000 cal. yr bp , which are interpreted to reflect shifts in the mean position of the Intertropical Convergence Zone (ITCZ) over the southern tropics. We suggest that this bioclimatic parameter has been the main driver of the vegetation dynamics in this area. The major inferred change occurred at the Younger Dryas–Holocene transition c . 11,800 cal. yr bp , when semi-deciduous forest disappeared, being replaced in the lake catchment by woodland, which persists to the present day in spite of locally high rainfall.
Main conclusions  In tropical regions under the influence of the ITCZ, the position and strength of which determine the distribution of rainfall through the year, more attention must be paid to the impact of the length and intensity of the dry season on the modern and past distribution and dynamics of the vegetation. This climatic parameter is as important as the total annual amount of rainfall, and probably one of the most relevant in lowland areas.     

Earliest Holocene vegetation history and island biogeography of the Isle of Man, British Isles

Aim To present radiocarbon dated early Holocene pollen analytical data from two sites on the northern plain of the Isle of Man and to discuss the implications of the vegetation history in relation to severance of the island from the British Isles and to identify further evidence for divergent biogeographical development previously exemplified by the survival and apparent dwarfism of late glacial Megaloceros giganteus (Giant Deer). Location The Isle of Man, British Isles. Methods Pollen analysis and AMS radiocarbon dating of late glacial to early Holocene lake sequences at Pollies and Curragh‐y‐Cowle on the northern plain of the Isle of Man. Results The pollen data indicate a prolonged period of pre‐woodland vegetation after the late Glacial/Holocene transition, which lasted for most of the first post‐glacial millennium. This persistence of pre‐forest environments meant that the expansion of Betula woodland occurred later in this part of the Isle of Man than in adjacent areas of Britain and Ireland. Conclusions The Isle of Man, in the northern Irish Sea, was isolated from Britain during the late Glacial period perhaps explaining the delayed arrival of tree species. Delayed rise of the Holocene forest compared with surrounding regions probably reflects severance of the land‐bridge with Cumbria, but also could be a function of climate changes during the early Holocene and local environmental conditions. Late survival and the dwarfism of the Megaloceros giganteus (Giant Deer) fauna is another example of biogeographical divergence during the early Holocene/late Glacial of the Isle of Man. The delayed afforestation and absence of human hunters in the Manx early Holocene offers a permissive environmental context for the as yet unproven survival of Megaloceros into the early Holocene.     

Sclerophyllous vegetation dynamics in the north of the Iberian peninsula during the last 16,000 years

We used pollen analysis to evaluate the dynamics of sclerophyllous arboreal taxa during the last 16,000 years. Quercus ilex type pollen and, to a lesser degree, other sclerophyllous elements (e.g. Olea and Phillyrea ) have been documented during the Late-glacial in the majority of the sequences obtained in continental territories in the north of the Iberian peninsula, as well as in the eastern coastal/sub-coastal area in the Cantabric region. During the Late-glacial and the Holocene, sclerophyllous elements became widespread in many areas of the north Iberian peninsula (the Sil, Duero and Ebro depressions and the southernmost slopes of adjacent mountains), with the smallest pollinic representation of these taxa being for the most septentrional areas (coastal/sub-coastal territories and the northermost slopes of the Cantabrian-Atlantic Mountains). During these periods, there is no indication of the presence of Quercus ilex pollen in the northwestern territories, which would explain the absence of this species in the present-day landscape. Despite the widespread distribution that sclerophyllous elements have maintained during the last 16,000 years, they have never attained a predominant role in the landscape, having a smaller representation, both during hotter and colder phases, than deciduous forests, pine forests and mixed forests.     

Causes and consequences of long-term climatic variability on the Australian continent

Summary 1. Ice-volume forced glacial–interglacial cyclicity is the major cause of global climate variation within the late Quaternary period. Within the Australian region, this variation is expressed predominantly as oscillations in moisture availability. Glacial periods were substantially drier than today with restricted distribution of mesic plant communities, shallow or ephemeral water bodies and extensive aeolian dune activity.
2. Superimposed on this cyclicity in Australia is a trend towards drier and/or more variable climates within the last 350 000 years. This trend may have been initiated by changes in atmospheric and ocean circulation resulting from Australia's continued movement into the Southeast Asian region and involving the onset or intensification of the El Niño-Southern Oscillation system and a reduction in summer monsoon activity.
3. Increased biomass burning, stemming originally from increased climatic variability and later enhanced by activities of indigenous people, resulted in a more open and sclerophyllous vegetation, increased salinity and a further reduction in water availability.
4. Past records combined with recent observations suggest that the degree of environmental variability will increase and the drying trend will be enhanced in the foreseeable future, regardless of the extent or nature of human intervention.     

The later Holocene history of vegetation, land-use and settlements around the Ahlequellmoor in the Solling area, Germany

A pollen diagram from the Ahlequellmoor in the Solling area shows the history of vegetation and settlement over the last 7,800 years. In the early Atlantic period mixed deciduous forest with mainly Tilia together with Ulmus and Quercus grew in the area. In the late Atlantic period Quercus became most abundant. Fagus spread in the Sub-boreal period at about 2700 B.C. Since ca. 900 B.C. the Solling was covered by beech forests with some oak. In prehistoric times woodland grazing is indicated. Only in Medieval times are two settlements in the vicinity of the Ahlequellmoor reflected in the pollen diagram. The earlier one is dated to about A.D. 750–1020, and may be connected with the former Monastery of Hethis, which is thought to have existed close to the fen from A.D. 815 to 822. The second Medieval settlement dates to the 11th–12th century. The large-scale woodland destruction of late Medieval and modern times is not clearly visible. The silvicultural measures of the last 200 years are reflected by increasing values of spruce and grassland taxa.