Susanne Jahns

Vegetation change in equatorial West Africa: time-slices for the last 150 ka

Abstract Drawing on marine and terrestrial palynological data, vegetation maps of equatorial West Africa are presented for eleven time slices over the last 150,000 years. Long marine records are used as a basis for the regional picture and provide a chronology for the last glacial cycle. Much shorter terrestrial records help fill in the picture for the most recent periods and facilitate interpretation of regional patterns for the longer timescale. Temporal and spatial variation is revealed in relation to global patterns of climate change. Rain forest was widespread during Oxygen Isotope Stages 1 and 5, but strongly reduced during Stages 3 and 4 and especially during Stages 2 and 6 when open, grass-rich vegetation prevailed. Glacial rain forest refuges are found in the southwest of the Guinean mountains and along the eastern coast of the Gulf of Guinea. Miombo woodland of the Zambezian vegetation zone expanded during Stage 5, especially during the first half. Podocarpus forest had its largest expansion during Substages 5d (115 to 105 ka) and 5b (95 to 85 ka). The last occurrence of Podocarpus in the Guinean mountains is during Stage 5a. The distribution of mangrove swamps was extremely reduced during glacial times. During Stage 6, savanna and open dry forest covered large areas along the northern coast of the Gulf of Guinea. The southern Saharan desert reached far to the south and the Namib desert far to the north. The area of rain forest was restricted, mangrove swamps were strongly reduced, and the area of Podocarpus forest fluctuated. During Stage 5 large changes in the area of Afromontane forest, rain forest, dry open forest and savanna occurred. Rain forest was widespread and mangroves were extensive along the coast during the last interglacial (Substage 5e). Podocarpus forest area strongly extended during Substages 5d and 5b. In Substages 5c and 5a, rain forest reclaimed areas it had lost in the previous substages (5d and 5b, respectively). Mangrove swamps were less widespread in the later substages of Stage 5 than during Substage 5e. During Stage 4, the rain forest area was again strongly reduced, and recovered only slightly during the following Stage 3. Also the mangrove swamp area was reduced except along the Ivory Coast and along the northwestern coast of the Gulf of Guinea. Podocarpus forest only occurred in Angola and may be in Congo during Stage 4. Again forest was much reduced during Stage 2 and open vegetation types covered large parts of equatorial West Africa. Mangrove swamps must have been rare. At the beginning of the Holocene, mangrove swamps had recovered and reached their largest extension. Also the rain forests area increased in the early Holocene and Guinean and Congolian rain forests were probably not separated by a savanna corridor now existing in Togo and Benin.

New palynological and tephrostratigraphical investigations of two salt lagoons on the island of Mljet, south Dalmatia, Croatia

In the sediments of both of the investigated lakes, the tephra from the Mercato-Ottaviano eruption (Vesuvius, southern Italy) (ca. 7900 B.P.) could be identified. The palynological investigations show that from ca. 9000-7200 B.P. (8000-6000 cal B.C.) deciduous oak forests predominated, with only a few representatives of Mediterranean vegetation. At the transition to the central European Atlantic Period those forests changed to an open vegetation type, dominated byJuniperus andPhillyrea. At about 5500 B.P. (4400 cal B.C.), theJuniperus-Phillyrea vegetation was replaced byQuercus ilex woodland that still occurs on the island of Mljet today and is considered to be the natural vegetation of the Dalmatian coastland. The associated vegetation of theQ. ilex forests changed several times. At the beginning of theQ. ilex period,Juniperus values were still high, but soon they decreased andErica spread. In more recent times theQ. ilex forests were partially replaced by plantations ofPinus halcpensis. Indicators of human impact are sparse throughout the pollen record. Clear evidence for human influence exists only from ca. 3100 B.P. (1300 cal B.C.) whenJuglans andPinus halepensis were introduced to the area. Later,Olea andSecale cultivation can be suggested and further spreading ofJuniperus indicates use of the land as pasture.

Vegetation history and climate changes in West Equatorial Africa during the Late Pleistocene and Holocene, based on a marine pollen diagram from the Congo fan

Palynological investigation of the marine core, GeoB 1008-3, from near the mouth of the Congo river (6°35.6′S/10°19.1′E), provides information about the changes in vegetation and climate in West Equatorial Africa during the last 190 ka. The pollen diagram is divided into zones 1–6 which are considered to correspond in time with the marine isotope stages 1–6. Oscillations in temperature and moisture are indicated during the cold stage 6. During stage 5, two cooler periods (5d and 5b) can be shown with an expansion of Podocarpus forests to lower elevations on the expense of lowland rain forest. Extended mangrove swamps existed along the coast in times of high sea level (stages 5 and 1).

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

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

The European Modern Pollen Database (EMPD) project

Modern pollen samples provide an invaluable research tool for helping to interpret the quaternary fossil pollen record, allowing investigation of the relationship between pollen as the proxy and the environmental parameters such as vegetation, land-use, and climate that the pollen proxy represents. The European Modern Pollen Database (EMPD) is a new initiative within the European Pollen Database (EPD) to establish a publicly accessible repository of modern (surface sample) pollen data. This new database will complement the EPD, which at present holds only fossil sedimentary pollen data. The EMPD is freely available online to the scientific community and currently has information on almost 5,000 pollen samples from throughout the Euro-Siberian and Mediterranean regions, contributed by over 40 individuals and research groups. Here we describe how the EMPD was constructed, the various tables and their fields, problems and errors, quality controls, and continuing efforts to improve the available data.

Late-glacial and Holocene woodland dynamics and land-use history of the Lower Oder valley, north-eastern Germany, based on two, AMS14C-dated, pollen profiles

High-resolution Holocene pollen profiles from lakes Großer Krebssee and Felchowsee, in the Lower Oder valley, north-eastern Germany, are presented. The Großer Krebssee profile includes a Late-glacial sequence. These investigations have been carried out in the context of a programme of archaeological excavation. AMS radiocarbon dates (26 in all) based on pollen concentrates have been used to provide a chronology for the pollen records. Holocene forest history and human impact are reconstructed for contrasting landscapes, namely, the Neuenhagener Oderinsel in the Lower Oderbruch (Großer Krebssee profile) and the more fertile Uckermärker Hügelland (Felchowsee profile) that lies immediately to the north. Both landscapes were glaciated during the Pomeranian stage of the Weichselian. New information on the spread of trees, includingTilia, Fagus and Carpinus, at both regional and local level, is presented. Five major phases of intensive human activity are recognised, the most intensive activity of the prehistoric period occurring in the Neolithic (Großer Krebssee profile). Differences between the records is explained in terms of local habitat, especially edaphic conditions, settlement history and also the pollen source area, the profile from the much larger Felchowsee lake providing a record of environmental change that is more regional in character.

Exploring holocene changes in palynological richness in northern Europe--did postglacial immigration matter?

In mid to high latitudes glacial and interglacial cycles have repeatedly changed the area available for plant growth. The speed at which plants are able to colonize areas at the onset of an interglacial is hypothesized to limit their distribution ranges even today (migrational lag). If the spread of plants would have been generally slow then plant diversity in previously glaciated areas would be expected to increase over time. We explore this hypothesis using results from six palynological investigations from two previously glaciated regions: central Sweden and north-eastern Germany. Rarefaction, slope of rank order abundance, and taxa accumulation plots were used to evaluate richness and evenness in pollen data in an attempt to separate richness from evenness. These analyses show little change in palynological richness for the northern sites throughout the Holocene. In contrast, the southern sites show an increase in richness and evenness during the early Holocene; this may be explained by the different initial conditions at the onset of the Holocene. A strong rise in palynological richness around 6000 and 1000 years ago at the southern sites can be attributed to the regional initiation of agriculture and major opening of the forest, respectively. For the northern sites there is no evidence for increased taxonomic diversity through time that could be due to delayed immigration of species.

A holocene pollen diagram from El Atrun, northern Sudan

Palynological investigations on a 3.36 m core from El Atrun, Nubia, show vegetation development and climatic change during a period from approximately 9800 to 7000 uncal B.P. From a dry period with a steppe-like vegetation at about 9800-9500 B.P. (zone A), a change to a period with a more favourable climate and a tree covered savanna-like vegetation can be observed in zone B (about 9500-8900 B.P.). In zone C (8900-8400 B.P.), a climatic setback is indicated, with spreading of steppe vegetation and an increase in swamp vegetation as a result of a low lake level. For zone D (about 8400-7000 B.P.), renewed spreading of wooded savanna is inferred.

On the Late Pleistocene and Holocene history of vegetation and human impact in the Ücker valley, north-eastern Germany

Abstract. A high-resolution Late Pleistocene and Middle to Late Holocene pollen profile of regional significance is presented. The coring site is located in a mire between two lakes. Ober- and Unter-Ückersee, in Brandenburg, north-eastern Germany. The study was carried out in an archaeological context. It provides information about the history of vegetation, climate and human impact in the Ücker river valley and the surrounding hills, the Uckermärker Hügelland. Hence, it is an important contribution for the reconstruction of the past vegetation of this area of Brandenburg. Seven AMS 14C-dates based on pollen concentrates provide a chronology for the middle Holocene part of the profile. Phases of intensive human activity can be shown from the middle Neolithic times until the Roman Iron Age.

Erratum to: The European Modern Pollen Database (EMPD) project

Unfortunately, the list of authors contains a number of duplications, omissions and other errors in the original publication of the article. The correct list appears in this erratum.