Holocene mangrove dynamics and environmental change in the Rufiji Delta, Tanzania

Holocene mangrove dynamics are reconstructed from pollen, sediment and radiocarbon analyses of three cores (ANR, BNR, CNR) located across a 20 km transect in the Rufiji Delta, Tanzania. At the base of the sediment sequence, dated to about 5600 cal. year b.p., the mangroves which are present suggest a low intertidal ecosystem in response to wet conditions and a higher sea level than at the present day. After around 5600 cal. year b.p. in core BNR, mangroves retreated seaward probably due to a lower sea level and drier environmental conditions. At around 4640 cal. year b.p., mangroves shifted landward suggesting a phase of sea level rise. In the late Holocene, mangroves became established at higher elevations of the Rufiji Delta, which is now a paddy field. Mangrove taxa decreased after 1170 cal. year b.p., suggesting drier conditions and less inundation frequency, possibly due to a lower sea level. Marked vegetation changes from mangroves to terrestrial vegetation occurred after around 750 cal. year b.p., possibly related to sea level regression and/or a desiccation phase recorded during the late Holocene. Paddy fields replaced mangroves in the landward part of the transect, reflecting an increase in human settlement in this area, a trend that continues to the present day. The recent decrease of mangrove species, particularly Rhizophora mucronata, could suggest less inundation by saline water and a lower sea level, although these changes may also be due to human activities during the last millennia as indicated by charcoal analysis.     

Holocene forest dynamics and human impact in southeastern Estonia

Litho-, chrono- and biostratigraphical methods were applied in the examination of a 9.9 m thick sequence of laminated sediments in Verijärv, a lake in southeast Estonia. The vegetation history, which covers at least the time from 10300 cal b.p. to the present, was inferred from the core, which was taken from the deepest part of the lake and correlated with the studied and dated pollen diagrams nearby. Reconstruction of the past vegetation dynamics is based on pollen percentage, accumulation rate and human impact diagrams. During the Holocene two main shifts in vegetation dynamics occurred, the first one at about 7700 cal b.p. when the pine-birch forest was replaced by deciduous mixed forest, and the second at about 3200 cal b.p. marked by the regeneration of pine-birch-spruce forest. A catastrophic forest fire at about 3450 cal b.p. opened up the landscape and gave rise to erosion and the sedimentation of a thick clayey layer. The steep decline in the Alnus curve between 1500–1650 cal b.p. coincides with the start of the continuous Secale curve and evidence of extensive land-use.     

Vegetation dynamics during the early to mid-Holocene transition in NW Malta, human impact versus climatic forcing

A pollen diagram was constructed for the early- to mid-Holocene transition (ca. 7350–5600 cal. b.p./5400–3650 b.c.) from the Burmarrad ria located in NW Malta. The vegetation at ca. 7350–6960 cal. b.p./5400–5010 b.c. was characterized by an almost tree-less steppe-like open landscape. Early Holocene dry climatic conditions were most probably due to intensification of the subtropical monsoon circulation that strengthened the subtropical anticyclonic descent over the central Mediterranean and blocked the penetration of humid air masses from the North Atlantic Ocean. At ca. 6950 cal. b.p./5000 b.c., the steppe-like vegetation was suddenly replaced by a Mediterranean evergreen forest or dense scrub dominated by Pistacia cf. lentiscus trees. This event, which has simultaneously been recorded in southern Sicily, was most probably caused by the southward shift of the ITCZ permitting the eastward movement of the North Atlantic cyclonic systems. Traces of human activities are evident in the pollen diagram since the beginning of the record but become more pronounced from the onset of the Temple Cultural Phase at ca. 6050 cal. b.p./4100 b.c. with a gradual decline of tree pollen. We suggest that the early- to mid-Holocene vegetation transformation was mainly controlled by a regional climatic change that occurred in a landscape only slightly impacted by human activities.     

Holocene climate,fire and vegetation dynamics at the treeline in the Northwestern Swiss Alps

Treelines are expected to rise to higher elevations with climate warming; the rate and extent however are still largely unknown. Here we present the first multi-proxy palaeoecological study from the treeline in the Northwestern Swiss Alps that covers the entire Holocene. We reconstructed climate, fire and vegetation dynamics at Iffigsee, an alpine lake at 2,065 m a.s.l., by using seismic sedimentary surveys, loss on ignition, visible spectrum reflectance spectroscopy, pollen, spore, macrofossil and charcoal analyses. Afforestation with Larix decidua and tree Betula (probably B. pendula) started at ~9,800 cal. b.p., more than 1,000 years later than at similar elevations in the Central and Southern Alps, indicating cooler temperatures and/or a high seasonality. Highest biomass production and forest position of ~2,100–2,300 m a.s.l. are inferred during the Holocene Thermal Maximum from 7,000 to 5,000 cal. b.p. With the onset of pastoralism and transhumance at 6,800–6,500 cal. b.p., human impact became an important factor in the vegetation dynamics at Iffigsee. This early evidence of pastoralism is documented by the presence of grazing indicators (pollen, spores), as well as a wealth of archaeological finds at the nearby mountain pass of Schnidejoch. Human and fire impact during the Neolithic and Bronze Ages led to the establishment of pastures and facilitated the expansion of Picea abies and Alnus viridis. We expect that in mountain areas with land abandonment, the treeline will react quickly to future climate warming by shifting to higher elevations, causing drastic changes in species distribution and composition as well as severe biodiversity losses.     

New insights into vegetation, climate and fire history of southern Brazil revealed by a 40,000 year environmental record from the State Park Serra do Tabuleiro

The present study reveals palaeoenvironmental changes in the coastal southern Brazilian highlands during the last 39720 b.p., by the means of pollen, charcoal and multivariate data analyses. The isolated mountain range of Serra do Tabuleiro corresponds to the southern distribution limit of many tropical plant species and is therefore sensitive to climate change. Palaeoenvironmental reconstructions from the Ciama 2 core at 860 m a.s.l. indicate that Campos (subtropical grassland) covered extensive areas on the highlands throughout the recorded glacial period, thus suggesting cold and dry climatic conditions. The initial development of the Atlantic rainforest occurred after the glacial period, whereas plant diversity began to increase at the beginning of the Holocene due to climate change towards warmer and wetter conditions. At about 10400 cal. b.p., the Atlantic rainforest started to move over the slopes and Campos retracted. Multivariate data analysis showed a change of vegetation dynamics after 11200 cal. b.p. with the initial development of the Atlantic rainforest continuing until the mid-Holocene. Major vegetation changes, including the further expansion of the Atlantic rainforest and the initial development of the Araucaria forest in the higher regions of the Serra do Tabuleiro, occurred during the late Holocene after about 3600 cal. b.p. These changes reflect higher precipitation levels without an annual dry season. Multivariate data analysis reveals a clearly directional change of vegetation dynamics corresponding to the progressive expansion of the Atlantic rainforest from 3850 to 1600 cal. b.p. A second directional change of vegetation dynamics occurred from 320 to 160 cal. b.p. (a.d. 1630 to 1790) with a further development of the Atlantic rainforest and the partial replacement of Campos by Araucaria forest and Atlantic rainforest. Thereafter, an ecosystem disturbance, which resulted in forest opening, took place. Palaeofires probably did not occur during glacial times, whereas fire events, which were probably caused by Amerindians, were common in the Serra do Tabuleiro region from ca. 10400 until 3600 cal. b.p.     

Vegetation and fire history with their implication for climatic change and fire events since the last deglacial in the Aso Valley, central Kyushu, southwestern Japan: new pollen and charcoal data

To better understand the response of forest vegetation to climate and fire regimes with reference to human activities over the last deglacial period in the Aso Caldera, central Kyushu, southwestern Japan, a 33.9 m long sediment core was examined in order to reconstruct the vegetational and fire history using pollen and charcoal analyses. The results show that a cool temperate broad-leaved deciduous forest, dominated by Quercus (deciduous oaks) with Carpinus and Fagus, prevailed in the Aso Valley from ca. 14.6 ka cal. b.p., indicating warming since the last glacial period. The landscape was presumably covered by a mosaic of deciduous Quercus forests and terrestrial Artemisia communities. Around 12.8–11.7 ka cal. b.p., Quercus dominated the forest and fires occurred frequently. Co-expansion of distinctive Ulmus–Zelkova and Celtis–Aphananthe forests coupled with a progressive retreat of Quercus in the early Holocene could reflect a strengthening of the East Asian summer monsoon under mild and humid climate conditions. Around 8 ka cal. b.p., significant increases in Cyclobalanopsis (evergreen oaks), Castanopsis/Castanea and Podocarpus indicate a further warming, in particular an increased winter temperature. Warm temperate lucidophyllous forests, dominated by Cyclobalanopsis, flourished after 7.3 ka cal. b.p., probably corresponding to the “Holocene Climatic Optimum” interval. Progressive expansion of Quercus at the expense of Cyclobalanopsis began around 6.4 ka cal. b.p. and paralleled an increase in charcoal until ca. 4.8 ka cal. b.p.; this could be evidence of fire disturbance induced by the early-middle Jomon people. The disturbed evergreen forest experienced a temporary recovery but then opened again from 3.6 ka cal. b.p. due to extensive fire deforestation, as suggested by the high charcoal levels during this time. Human exploitation and buckwheat (Fagopyrum) agriculture may have contributed to the opening of the forest, which allowed secondary forests (primarily Pinus and Quercus) and herbaceous communities (mainly Poaceae) to spread. These results are discussed in comparison with other high-resolution pollen data from western Japan to better elucidate the vegetation and fire history over the last deglacial in the Aso Caldera.     

Holocene history of environment and human impact on two islands in the Ostholstein lakeland area, Northern Germany

Holocene sediment cores from contemporary terrestrialised kettle holes on two islands in the Ostholstein lakeland area, Northern Germany, were investigated by palaeoenvironmental methods. Records from such isolated locations, such as these island mires, are an important source of information on small-scale vegetation changes. Pollen, non-pollen palynomorphs and macrofossils were used to reveal anthropogenic impact as well as lake level fluctuations. Changes in the peat decomposition and the ratio of organic to minerogenic content in the sediment facilitated correlation with past ground water table levels and accordingly with former lake levels. The palynological surveys indicate that human impact on the islands expanded in prehistoric times during phases of low lake levels or periods of stable hydrological conditions. The first distinct low level is recorded between ca. 8210 and 7740?cal.?yr b.p. Another major low level period was detected for the time span from approximately 5290 to 4600?cal.?yr b.p. After a subsequent period with a wetter climate, indicated by rising and fluctuating lake levels culminating at ca. 2420 to 2180?cal.?yr b.p., a third lowering occurred until about 660?cal.?yr b.p. This period was interrupted by minor fluctuations in lake levels from ca. 1770 to 1630?cal.?yr b.p. and from ca. 1370 to 1010?cal.?yr b.p.     

New insights into vegetation dynamics and settlement history in Hümmling,north-western Germany,with particular reference to the Neolithic

Palynological investigations on two well-dated peat profiles provide insights into Neolithic vegetation and settlement history from Hümmling in north-western Germany. The site selections allow comparisons between local and regional vegetation changes and are used to estimate the extent of Neolithic influence on the vegetation. The interpretation of the fossil spectra relied on radiocarbon dating, evaluation of pollen indicator taxa, non-pollen palynomorphs and multivariate techniques. During the late Mesolithic the vegetation was dominated by mixed oak forests while openings in forest cover were detected, with a decline in elm reflected in the regional pollen record around 4250 cal. b.c. The presence of humans is shown by settlement indicators that are first recorded at ca. 3800 cal. b.c. Vegetation changes were small between 4300 and 3600 cal. b.c. This suggests that regional vegetation was relatively resilient to small-scale disturbances. Possible indications of grazing were recorded in the spectra of the local pollen profile but there is no clear-cut evidence for Neolithic activity. Between 3520 and 2260 cal. b.c. decreases in forest cover were inferred from both profiles and increases in settlement indicators reflect farming activity. These changes coincide with the emergence in the area of the Funnel Beaker Culture and the subsequent Single Grave Culture. Both profiles suggest that settlement probably ceased between ca. 3230 and 3050 cal. b.c. This lull or cessation in activity was probably regional in character. After 2260 cal. b.c. human impact on the vegetation decreases and woodlands regenerate. The longevity of the regeneration phase—ca. 690 years—was probably connected with the low resilient capability of the vegetation on the poor soils.     

18,000 years of grassland evolution in the summer rainfall region of South Africa: evidence from Mahwaqa Mountain,KwaZulu-Natal

A palynological and sedimentological record from the Mahwaqa Mountain in KwaZulu-Natal, South Africa, provides evidence of the vegetation dynamics in this part of the Grassland Biome during the last c. 18,000 years. The wetland is located at 1,850 m on an isolated outlier of the Ukhahlamba–Drakensberg Mountain range on an ecotone along a climatic gradient. The vegetation responded to humidity and temperature changes during the late Pleistocene and Holocene. The period c. 18,000–13,500 cal. bp is characterized by high Ericaceae and Restionaceae percentages and decreasing values of charred particles, indicating cool conditions. Around 13,500–8,500 cal. bp, Ericaceae were gradually replaced by Poaceae, signaling climate warming. Growing environmental wetness during the same time period is inferred from Phragmites-type and Cliffortia pollen percentages. Since c. 8,500 cal. bp, Cliffortia, Restionaceae, and Phragmites-type percentages have maintained low levels. Ericaceae were almost completely replaced by grasses and Asteraceae by c. 7,500 cal. bp. All indications are that warm and fluctuating moisture conditions followed until 4,600 cal. bp but they became driest between c. 4,600 and 3,500 cal. bp, when high Asteraceae, Pentzia-type and Scabiosa percentages were prominent. From c. 3,500–800 cal. bp, the increase of sedges, Aponogeton and grass pollen (including Phragmites-type) at the expense of Asteraceae pollen suggests the return of slightly more humid conditions. Since c. 1,000 cal. bp an increase of water demanding Podocarpus and Cliffortia occurred. Pine pollen indicates the recent introduction of alien plants in the 19th and 20th centuries.     

Postglacial history of vegetation,human activity and lake-level changes at Jezioro Linówek in northeast Poland,based on multi-proxy data

We present the postglacial history of vegetation, human activities and changes in lake level in the context of climate change in northeast Poland from ~14,000 cal. b.p. to the present day. The palaeoecological reconstruction is based on the results of high-resolution plant macrofossil analyses as well as records from pollen, Cladocera and radiocarbon dating. Climate fluctuations and human activity have caused many changes in vegetation development in Jezioro Linówek and in the vicinity of this lake. The Early Holocene warming that occurred at ~9500 b.c. caused an increase in Betula and the colonisation of Linówek by Potamogeton lucens, Nymphaea alba and Chara sp. At ~2300 b.c., climate cooling was accompanied by the spread of Picea abies and the appearance of Potamogeton alpinus and Nuphar pumila in the lake. The first traces of farming in the form of Cerealia pollen have been dated back to ~2100 b.c. The cultivation of Triticum began at ~250 b.c., Secale at ~a.d. 550, and Fagopyrum at ~a.d. 1720. The rapid increase in human activity at ~a.d. 1700 and the simultaneous loss of woodland is associated with the establishment of villages in the area and is expressed by the decline of tree curves. In Linówek, which was formed ~14,000 cal. b.p., three periods of high water level occurred (12000–9400, 7000–4000 and 1450 b.c.–a.d. 650), and two periods of low water level (9400–7100 and 3700–1700 b.c.). The changes of water level correspond well with other sites in central and northern Europe.     

Palaeoecological evidence for the middle and late Holocene vegetation, climate and land use in the upper Don River basin (Russia)

New pollen and plant macrofossil data, backed by radiocarbon dates, from the Kulikovo battlefield area in the forest-steppe region of the Upper Don River basin (central part of European Russia) indicate that the area was covered by mosaic vegetation in the second half of the Holocene. Steppe communities dominated during the mid—late Atlantic (7.2–5.7?cal.?kyr b.p.) and early Subatlantic (2.7–2.4?cal.?kyr b.p.), while forest-steppe dominated during the Subboreal (2.7–5.7?cal.?kyr b.p.), middle and late Subatlantic (2.4?cal.?kyr b.p. – present). Climatic reconstructions based on these data show that landscape dynamics in the region were most probably driven by changes in effective moisture: an excess of precipitation over evaporation. Even small reductions in annual precipitation, accompanied by a rise in summer temperatures by 1–3°C above present values, were sufficient to increase the proportion of steppe communities within this landscape complex, and also probably resulted in higher frequencies of wildfires. Signals of anthropogenic disturbance of vegetation are clearly pronounced in the pollen and plant macrofossil records since the middle Atlantic. However, human-induced changes in the vegetation remain subtle until the medieval period.     

Holocene salt marsh plant communities in the North Adriatic coastal plain (Italy) as reflected by pollen, non-pollen palynomorphs and plant macrofossil analyses

In this work we investigate the development of a salt marsh environment during the Holocene marine transgression in the North Adriatic coast (North Italy) near the pre-Roman and Roman towns of Cittanova and Concordia Sagittaria. Pollen, plant macrofossils, non-pollen palynomorphs (NPPs) and foraminifers are analysed in cores and archaeological excavations to indicate the development of salt marsh plant communities. Other independent proxies (foraminifers, plant macrofossils, molluscs) confirm the ecological interpretation based on pollen records. The relevance of NPPs as indicators of salt marsh environment is evaluated. Linings of foraminifers are the most frequent NPP type, recorded in 85% of the brackish sediments. They may tentatively be referred to the genus Ammonia, a very common benthonic genus in the present lagoons of the North Adriatic Sea. Radiocarbon dates available from previous work allow the salt marsh development to be dated in the sector from the east of the Lagoon of Venice to the Lagoon of Caorle. Near Cittanova, salt marshes developed before 6700 yrs cal. b.p. At Concordia Sagittaria, the first evidence dates from ca. 6700 yrs cal. b.p. and a phase of freshwater conditions is recorded in the sediments of ca. 4500 yrs cal. b.p.     

Early–Middle Holocene vegetation history, climate change and human activities at Lago Riane (Ligurian Apennines, NW Italy)

The radiocarbon-dated palaeoecological study of Lago Riane (Ligurian Apennines, NW Italy) presented here forms part of a wider investigation into the relationships between Holocene vegetation succession, climate change and human activities in the northern Apennines. The record of vegetation history from Lago Riane indicates that, since the end of the last glaciation, climate change and prehistoric human activities, combined with several local factors, have strongly influenced the pattern and timing of natural vegetation succession. The pollen record indicates an important change in vegetation cover at Lago Riane at ~8500–8200 cal. years b.p., coincident with a well-known period of rapid climate change. At ~6100 cal. years b.p., Fagus woodland colonised Lago Riane during a period of climate change and expansion of Late Neolithic human activities in the upland zone of Liguria. A marked decline in Abies woodland, and the expansion of Fagus woodland, at ~4700 cal. years b.p., coincided with further archaeological evidence for pastoralism in the mountains of Liguria during the Copper Age. At ~3900–3600 cal. years b.p. (Early to Middle Bronze Age transition), a temporary expansion of woodland at Lago Riane has been provisionally attributed to a decline in human pressure on the environment during a period of short-term climate change.     

The forest people: landscape and firewood use in the Araruama region,southeastern Brazil,during the late Holocene

The site of Morro Grande, situated in the Araruama region, southeastern Brazil (22º47′07″S, 42º21′49″W), is in the Atlantic rainforest phytogeographical domain. It is attributed to proto-Tupinambá agriculturalist and ceramicist populations, recognized by their typical polychrome ceramics. Four periods of occupation were identified at this site: (1) 3,220–2,840 cal b.p.; (2) 3,000–2,150 cal b.p.; (3) 1,820–1,390 cal b.p.; and (4) c. 750 cal. b.p. Analysis of 3,908 charcoal fragments from the three earlier periods has allowed the identification of 78 taxa and 29 plant families. This work demonstrates the permanence of the Atlantic rainforest in the region between 3,220 and 1,390 cal b.p., confirming previous palaeoenvironmental studies in southeastern and southern Brazil. The existence of mature forests is demonstrated; however, firewood was collected mainly from secondary vegetation, probably in the area surrounding the settlement or from cultivated land. These results provide further evidence of human influence on Neotropical rainforests. Creation of secondary environments, however, did not result in irreversible damage to local biodiversity, since the forest tended to regenerate after the clearings were abandoned. Analysis of charcoal concentrated in features allowed the identification of ritual funerary hearths, as well as of a probable specialized feature for firing ceramics. This evidence affords new perspectives for the archaeological interpretation of the funerary ritual and way of life of proto-Tupinambá people.     

Vegetation history and landscape management from 6500 to 1500 cal. b.p. at Lac d’Antre, Gallo-Roman sanctuary of Villards d’Héria, Jura, France

The lake sediment record was used to reconstruct past vegetation dynamics and human impacts from the middle Neolithic (6500 cal. b.p.) to the Middle Ages (1500 cal. b.p.) around Lac d’Antre in the southern Jura mountains of France. This lake was surrounded by the Gallo-Roman sanctuary of Villards d’Héria, which has been widely investigated by archaeologists and enables a comparison between palaeoenvironmental proxies and archaeological data. Pollen and microscopic charcoal analyses were conducted on a 500 cm sediment core with eleven radiocarbon dates providing the chronological control. In a mixed oak woodland context, the successive development of Taxus, Fagus and Abies were mainly caused by climatic variations during the Neolithic, in which there was weak human impact. The first significant signs of human activity were detected during the Bronze Age from 3900 cal. b.p., followed by an increase of human pressure and woodland clearances during the Iron Age, from 2700 cal. b.p. The occupation of the Gallo-Roman sanctuary was continuous with the Iron Age occupation. All the analysed palaeoenvironmental data indicate that the strongest human impact occurred during the Gallo-Roman period, which matches the occupation of Villards d’Héria previously dated by archaeologists from 2000 to 1700 cal. b.p., 1st to 3rd century a.d. Moreover, there appears to have been a new period of human settlement close to the lake at the beginning of the Middle Ages. The low charcoal accumulation rate (CHAR) recorded during the Bronze and Iron Ages suggests that fire was not the main agent used to clear the dense woods to create new cultivated fields and pastures. High CHAR values recorded during the Roman period may represent fire use for domestic and agro-pastoral activities.     

Mid-Holocene vegetation change in the Troad (W Anatolia): man-made or natural?

New wood charcoal data from two archaeological sites in western Anatolia (Kumtepe and Troy/Çanakkale province) enabled a review of earlier reconstruction of the mid-Holocene vegetation and land use patterns in the region. Multi-proxy data from archaeology, zooarchaeology and climatology are combined to evaluate the relationship of climate-induced and man-made environmental change for a period spanning the Late Neolithic to the Early Bronze Age (ca. 5000–2450 cal b.c.). During the first settlement period (Kumtepe A: ca. 5000–4600 cal b.c.) lush vegetation with high proportions of deciduous oak and pine prevailed, enabling the intense use of natural resources by the late Neolithic population, which use might be reflected in the first few representatives of maquis vegetation. A settlement hiatus at the site between roughly 4600 and 3500 cal b.c. includes a cooling event in the Aegean and may have supported persistence and/or development of open vegetation units. However, the hiatus may have ended with a period of regeneration of the vegetation. From Kumtepe B2 (ca. 3300 cal b.c.) onward, human impact becomes clearly visible, although the main woodland taxa continue to prevail. In all, environmental and economic dynamics between 5000 and 2300 cal b.c. in the Troad can be characterised as at least two alternating developmental sequences of climate-induced vegetation change and reinforcement of woodland degradation by human activity.     

Late Quaternary environmental history of the south-eastern Tibetan Plateau inferred from the Lake Naleng non-pollen palynomorph record

A 17.81 m sediment core from Lake Naleng, a freshwater lake in the south-eastern part of the Tibetan Plateau was examined for its non-pollen palynomorph (NPP) composition. The frequencies of 15 NPPs and three aquatic pollen types were determined in 160 samples. Since the origin of several NPP types is still unknown, multivariate analysis, supported by findings from the corresponding fossil pollen flora, was carried out to extract information about their ecological environments. The analysis allowed a classification of all microfossils in four groups of environmental response, which provided an approach to tracing lake history and palaeoclimatic changes in the area since the Late Glacial (since 17,700 cal years b.p.). Unstable lake conditions and a low organic productivity were reconstructed for the Late Glacial before 14,600 cal years b.p. with high inputs of terrestrial material. Climate conditions became wetter during the Bølling/Allerød interval indicated by high productivity in the lake. After a short climate deterioration (12,500–11,500 cal years b.p.), stable lake conditions were inferred from the record. During the late Holocene (since 2,700 cal years b.p.) changes in the NPP composition might be related to human impact, the latter being inferred from the pollen data through the presence of grazing indicators.     

Sensitivity of Bolivian seasonally-dry tropical forest to precipitation and temperature changes over glacial–interglacial timescales

We used fossil pollen to investigate the response of the eastern Chiquitano seasonally-dry tropical forest (SDTF), lowland Bolivia, to high-amplitude climate change associated with glacial–interglacial cycles. Changes in the structure, composition and diversity of the past vegetation are compared with palaeoclimate data previously reconstructed from the same record, and these results shed light on the biogeographic history of today’s highly disjunct blocks of SDTF across South America. We demonstrate that lower glacial temperatures limited tropical forest in the Chiquitanía region, and suggest that SDTF was absent or restricted at latitudes below 17°S, the proposed location of the majority of the hypothesized ‘Pleistocene dry forest arc’ (PDFA). At 19500 yrs b.p., warming supported the establishment of a floristically-distinct SDTF, which showed little change throughout the glacial–Holocene transition, despite a shift to significantly wetter conditions beginning ca. 12500–12200 yrs b.p. Anadenanthera colubrina, a key SDTF taxon, arrived at 10000 yrs b.p., which coincides with the onset of drought associated with an extended dry season. Lasting until 3000 yrs b.p., Holocene drought caused a floristic shift to more drought-tolerant taxa and a reduction in α-diversity (shown by declining palynological richness), but closed-canopy forest was maintained throughout. In contrast to the PDFA, the modern distribution of SDTF most likely represents the greatest spatial coverage of these forests in southern South America since glacial times. We find that temperature is a key climatic control upon the distribution of lowland South American SDTF over glacial-interglacial timescales, and seasonality of rainfall exerts a strong control on their floristic composition.     

The Iron Age in the Mrągowo Lake District,Masuria, NE Poland: the Salęt settlement microregion as an example of long-lasting human impact on vegetation

Pollen, non-pollen palynomorphs, charcoal and geochemical analyses of sediments from Lake Sal?t (NE Poland) were used to reconstruct vegetation changes related to the activity of the West Balt tribes during the Iron Age, in the period between the second half of the 7th century bc and the beginning of the 10th century ad. We distinguished five phases of human impact on environment. Woodland clearing around the studied lake started at the end of the 7th century bc. The most characteristic feature of this area during the whole Iron Age was a very high representation of semi-natural Betula woodlands, which was probably linked to a shifting agriculture. This type of land use lasted for over 1,500 years, until the second half of the 9th century ad. The greatest reduction in Betula woodlands took place between cal. years 650 and 450 bc. Its regeneration took place after ca. ad 830 when human activity decreased.     

Inter-proxy evidence for the development of the Amazonian mangroves during the Holocene

The dynamics of mangrove forest on the island of Marajó (Ilha de Marajó) at the mouth of the river Amazon during the past ~7,500 cal. b.p. were studied using multiple proxies, including sedimentary facies, pollen, δ¹³C, δ¹⁵N and C/N ratio, related to 15 sediment samples by ¹⁴C dating. The results allow us to propose a scheme of palaeogeographical development, with changes in vegetation, hydrology and organic matter dynamics. Today, the interior of the island is occupied by várzea freshwater herbaceous vegetation, but during the early to middle Holocene, mangroves with accumulations of estuarine organic matter colonized the tidal mud flats. This spread of mangroves was caused by post-glacial sea-level rise, which combined with tectonic subsidence, produced a marine transgression. It is likely that the relatively greater marine influence at the studied area was favoured by reduced discharge from the river Amazon, which was itself caused by a dry period that occurred during the early and mid Holocene. During the late Holocene, there was a reduction of mangrove vegetation and the contribution of freshwater organic matter to the area was higher than during the early and mid Holocene. This suggests a decrease in marine influence during the late Holocene which led to a gradual migration of mangrove vegetation from the central region to the northeastern littoral zone of the island, and, consequently, its isolation since at least ~1,150 cal. b.p. This was probably a result of lower tidal water salinity caused by a wet period that resulted in greater river discharge during the late Holocene. This work details the contraction of mangrove forest from the northeastern part of the island of Marajó under the influence of Amazon climatic changes, chronologically and spatially. This allows us to propose a model of successive phases of sediment accumulation and vegetation change, according to the marine-freshwater influence gradient. As demonstrated by this work, the use of a combination of proxies is efficient for establishing a relationship between the changes in estuarine salinity gradient and depositional environment/vegetation.