7000-year human legacy of elevation-dependent European fire regimes

Variability in fire regime at the continental scale has primarily been attributed to climate change, often overshadowing the widely potential impact of human activities. However, human ignition modifies the rhythm of fire episodes occurrence (fire frequency), whereas land use alters vegetation composition and fuel load, and thus the amount of biomass burned. It is unclear, however, whether and how humans have exercised a significant influence over fire regimes at continental and millennial scales. Based on sedimentary charcoal records, we use new alternative estimate of fire frequency and biomass burned for the last 16000 years (here after 16 ky) that we evaluate with outputs from climate, vegetation, land use and population models. We find that pronounced regional-scale land use changes in southern Europe at the beginning of the Neolithic (8–6 ky), during the Bronze Age (5–4 ky) and the medieval period (1 ky) caused a doubling of fire frequency compared to the Holocene average (the last 11.5 ky). Despite anthropogenic influences, southern European biomass burned decreased from 7 ky, which is in line both with changes in orbital parameters leading climate cooling and also reductions in biomass availability because of land use. Our study underscores the role of elevation-dependent parameters, and particularly biomass and land management, as major drivers of fire regime variability. Results attest a determinant anthropogenic driving-force on fire regime and a decrease in fire-carbon emissions since 7 ky in Southern Europe.

Reconstruction of Holocene vegetation dynamics at Lac de Bretaye, a high-mountain lake in the Swiss Alps

A deeper understanding of past vegetation dynamics is required to better assess future vegetation responses to global warming in the Alps. Lake sediments from Lac de Bretaye, a small subalpine lake in the Northern Swiss Alps (1780 m a.s.l.), were analysed to reconstruct past vegetation dynamics for the entire Holocene, using pollen, macrofossil and charcoal analyses as main proxies. The results show that timberline reached the lake’s catchment area at around 10,300 cal. BP, supporting the hypothesis of a delayed postglacial afforestation in the Northern Alps. At the same time, thermophilous trees such as Ulmus, Tilia and Acer established in the lowlands and expanded to the altitude of the lake, forming distinctive boreo-nemoral forests with Betula, Pinus cembra and Larix decidua. From about 5000 to 3500 cal. BP, thermophilous trees declined because of increasing human land use, mainly driven by the mass expansion of Picea abies and severe anthropogenic fire activity. From the Bronze Age onwards (c. 4200–2800 cal. BP), grazing indicators and high values for charcoal concentration and influx attest an intensifying human impact, fostering the expansion of Alnus viridis and Picea abies. Hence, biodiversity in alpine meadows increased, whereas forest diversity declined, as can be seen in other regional records. We argue that the anticipated climate change and decreasing human impact in the Alps today will not only lead to an upward movement of timberline with consequent loss of area for grasslands, but also to a disruption of Picea abies forests, which may allow the re-expansion of thermophilous tree species.

Holocene vegetation and fire history of the mountains of Northern Sicily (Italy)

Knowledge about vegetation and fire history of the mountains of Northern Sicily is scanty. We analysed five sites to fill this gap and used terrestrial plant macrofossils to establish robust radiocarbon chronologies. Palynological records from Gorgo Tondo, Gorgo Lungo, Marcato Cixé, Urgo Pietra Giordano and Gorgo Pollicino show that under natural or near natural conditions, deciduous forests (Quercus pubescens, Q. cerris, Fraxinus ornus, Ulmus), that included a substantial portion of evergreen broadleaved species (Q. suber, Q. ilex, Hedera helix), prevailed in the upper meso-mediterranean belt. Mesophilous deciduous and evergreen broadleaved trees (Fagus sylvatica, Ilex aquifolium) dominated in the natural or quasi-natural forests of the oro-mediterranean belt. Forests were repeatedly opened for agricultural purposes. Fire activity was closely associated with farming, providing evidence that burning was a primary land use tool since Neolithic times. Land use and fire activity intensified during the Early Neolithic at 5000 bc, at the onset of the Bronze Age at 2500 bc and at the onset of the Iron Age at 800 bc. Our data and previous studies suggest that the large majority of open land communities in Sicily, from the coastal lowlands to the mountain areas below the thorny-cushion Astragalus belt (ca. 1,800 m a.s.l.), would rapidly develop into forests if land use ceased. Mesophilous Fagus-Ilex forests developed under warm mid Holocene conditions and were resilient to the combined impacts of humans and climate. The past ecology suggests a resilience of these summer-drought adapted communities to climate warming of about 2 °C. Hence, they may be particularly suited to provide heat and drought-adapted Fagus sylvatica ecotypes for maintaining drought-sensitive Central European beech forests under global warming conditions.

Grain size analyses, Ca/Ti and other selected elemental ratios from XRF core scanning of sediment cores from the Apulian Margin

An extensive, high-resolution, sedimentological-geochemical survey was done using geo-acoustics, XRF-core scans, ICP-AES, AMS 14C-dating and grain size analyses of sediments in 11 cores from the Gulf of Taranto, the southern Adriatic Sea, and the central Ionian Sea spanning the last 16 cal. ka BP. Comparable results were obtained for cores from the Gallipoli Shelf (eastern Gulf of Taranto), and the southern Adriatic Sea suggesting that the dominant provenance of Gallipoli Shelf sediments is from the western Adriatic mud belt. The 210Pb and 14C-dated high-accumulation-rate sediments permit a detailed reconstruction of climate variability over the last 16 cal. ka BP. Although, the Glacial-Interglacial transition is generally dry and stable these conditions are interrupted by two phases of increased detrital input during the Bølling-Allerød and the late Younger Dryas. The event during the Younger Dryas period is characterized by increased sediment inputs from southern Italian sources. This suggests that run-off was higher in southern- compared to northern Italy. At approximately ~ 7 cal. ka BP, increased detrital input from the Adriatic mud belt, related to sea level rise and the onset of deep water formation in the Adriatic Sea, is observed and is coincident with the end of sapropel S1 formation in the southern Adriatic Sea. During the mid-to-late Holocene we observed millennial-scale events of increased detrital input, e.g. during the Roman Humid Period, and of decreased detrital input, e.g., Medieval Warm Period. These dry/wet spells are consistent with variability in the North Atlantic Oscillation (NAO). A negative state of the NAO and thus a more advanced penetration of the westerlies into the central Mediterranean, that result in wet conditions in the research area concord with events of high detrital input e.g., during the Roman Humid Period. In contrast, a positive state of the NAO, resulting in dry conditions in the Mediterranean, dominated during events of rapid climate change such as the Medieval Warm Period and the Bronze Age.

Pollen records from Elbe-Weser Dreieck

A long-running interdisciplinary research project on the development of landscape, prehistoric habitation and the history of vegetation within a "siedlungskammer" (limited habitation areal from neolithic to modern times has been carried out in the NW German lowlands, The siedlungskammer Flögeln is situated between the rivers Weser and EIbe and comprises about 23.5 km^2. It is an isolated pleistocene area surrounded by bogs, the soils consisting mainly of poor sands. In this siedlungskammer large-seale archaeological excavations and mappings have been performed, parallel to pedological, historical and above all pollen analytical investigations. The aim of the project is to record the individual phases in time, to delimit the respective settlement areas and to reconstruct the conditions of life and economy for each time period. A dense network of 10 pollen diagrams has been constructed. Several of them derive from the marginal area and from the centre of the large raised bog north of the siedlungskammer. These diagrams reflect the history of vegetation and habitation of a large region; due to the large pollen source area the habitation phases in the diagrams are poorly defined. Even in the utmost marginal diagram of this woodless bog, a great village with adjoining fields, situated only 100 m away from it, is registered with only low values of anthropogenic indicators. In contrast to this, the numerous pollen diagrams from kettle-hole bogs inside the siedlungskammer yield an exact picture of the habitation of the siedlungskammer and their individual parts. Early traces of habitation can be identified in the pollen diagram soon after the elm decline (around 5190 BP). Some time later in the middle neolithic period there follows a marked habitation phase, which starts between 4500 and 4400 BP and reflects the immigration of the trichterbecher culture. It corresponds to the landnam phase of Iversen in Denmark and begins with a sharp decline of the pollen curves of lime and oak, followed by the increase of anthropogenic indicators pointing to arable and pastural farming. High values of wild grasses and Calluna witness extensive forest grazing. This middle to late neolithic habitation is also registered archaeologically by settlements and numerous graves. After low human activity during Bronze Age and Older Iron Age times the archaeological and pollen analytical records of Roman and Migration periods is again very strong. This is followed by a gap in habitation during the 6th and 7th centuries and afterwards in the western part of the siedlungskammer from about 700 AD until the 14th century by the activity of the medieval village of Dalem, that was also excavated and whose fields were recorded by phosphate mapping to a size of 117 hectares. This medieval settlement phase is marked by much cereal cultivation (mainly rye). The dense network of pollen diagrams offers an opportunity to register the dispersion of the anthropogenic indicators from the areas of settlement to different distances and thus to obtain quantitative clues for the assessment of these anthropogenic indicators in pollen diagrams. In fig. 4 the reflection of the neolithic culture in the kettle-hole bogs and the large raised bog is shown in 3 phases: a) pre landnam, b) TRB-landnam, c) post landnam. Among arboreal pollen the reaction of Quercus is sharp close to the settlement but is not found at more distant profiles, whilst in contrast to this Tilia shows a significant decline even far away from the settlements. The record of most anthropogenic indicators outside the habitation area is very low, in particular cereal pollen is poorly dispersed; much more certain as an indicator for habitation (also for arable farming!) is Plantago lanceolata. A strong increase of wild grasses (partly Calluna aswell) some distance from the habitation areas indicates far reaching forest grazing. Fig. 5 illustrates the reflection of the anthropogenie indicators from the medieval village Dalem. In this instance the field area could be mapped exactly using phosphate investigations, and it has been possible to indicate the precise distances of the profile sites from the medieval fields. Here also, there is a clear correlation between decreasing anthropogenic indicators and increasing distance. In a kettle-hole bog (FLH) a distance of 3000 m away this marked settlement phase is not registered. The contrast between the pollen diagrams SWK and FLH (fig. 2 + 3, enclosure), illustrates the strong differences between diagrams from kettlehole bogs close to and distant from the settlements, for the neolithic as well as for the medieval period. On the basis of the examples presented here, implications concerning the interpretation of pollen diagrams with respect to habitation phases are discussed.

Determination of ages and fossil Coleoptera fauna from eight sites in the London region

These data sets report the fossil beetle assemblages identified from the Mesolithic to Late Bronze Age at eight sites in the London region. All but one of the study sites are within 2 km of the modern course of the Thames. The sites produced 128 faunal assemblages that yielded 218 identified species in 41 families of Coleoptera (beetles).  Beetle faunas of Mesolithic age indicate extensive wetlands near the Thames, bordered by rich deciduous woodlands. The proportion of woodland species declined in the Neolithic, apparently because of the expansion of wetlands, rather than because of human activities. The Early Bronze Age faunas contained a greater proportion of coniferous woodland and aquatic (standing water) species. An increase in the dung beetle fauna indicates the presence of sheep, cattle and horses, and various beetles associated with crop lands demonstrate the local rise of agriculture, albeit several centuries after the beginnings of farming in other regions of Britain. Late Bronze Age faunas show the continued development of agriculture and animal husbandry along the lower Thames. About 33% of the total identified beetle fauna from the London area sites have limited modern distributions or are extinct in the U.K. Some of these species are associated with the dead wood found in primeval forests; others are wetland species whose habitat has been severely reduced in recent centuries. The third group is stream-dwelling beetles that require clean, clear waters and river bottoms.

World distribution of land cover changes, model in NetCDF format

The role of Pre- and Protohistoric anthropogenic land cover changes needs to be quantified i) to establish a baseline for comparison with current human impact on the environment and ii) to separate it from naturally occurring changes in our environment. Results are presented from the simple, adaptation-driven, spatially explicit Global Land Use and technological Evolution Simulator (GLUES) for pre-Bronze age demographic, technological and economic change. Using scaling parameters from the History Database of the Global Environment as well as GLUES-simulated population density and subsistence style, the land requirement for growing crops is estimated. The intrusion of cropland into potentially forested areas is translated into carbon loss due to deforestation with the dynamic global vegetation model VECODE. The land demand in important Prehistoric growth areas - converted from mostly forested areas - led to large-scale regional (country size) deforestation of up to 11% of the potential forest. In total, 29 Gt carbon were lost from global forests between 10 000 BC and 2000 BC and were replaced by crops; this value is consistent with other estimates of Prehistoric deforestation. The generation of realistic (agri-)cultural development trajectories at a regional resolution is a major strength of GLUES. Most of the pre-Bronze age deforestation is simulated in a broad farming belt from Central Europe via India to China. Regional carbon loss is, e.g., 5 Gt in Europe and the Mediterranean, 6 Gt on the Indian subcontinent, 18 Gt in East and Southeast Asia, or 2.3 Gt in subsaharan Africa.

Simulated transition to agropastoralism in the Indus valley 7500-3000 BC

The Indus Valley Civilization (IVC) was one of the first great civilizations in prehistory. This bronze age civilization flourished from the end of the fourth millennium BC. It disintegrated during the second millennium BC; despite much research effort, this decline is not well understood. Less research has been devoted to the emergence of the IVC, which shows continuous cultural precursors since at least the seventh millennium BC. To understand the decline, we believe it is necessary to investigate the rise of the IVC, i.e., the establishment of agriculture and livestock, dense populations and technological developments 7000-3000 BC. Although much archaeologically typed information is available, our capability to investigate the system is hindered by poorly resolved chronology, and by a lack of field work in the intermediate areas between the Indus valley and Mesopotamia. We thus employ a complementary numerical simulation to develop a consistent picture of technology, agropastoralism and population developments in the IVC domain. Results from this Global Land Use and technological Evolution Simulator show that there is (1) fair agreement between the simulated timing of the agricultural transition and radiocarbon dates from early agricultural sites, but the transition is simulated first in India then Pakistan; (2) an independent agropas- toralism developing on the Indian subcontinent; and (3) a positive relationship between archeological artifact richness and simulated population density which remains to be quantified.

Mineral and organic geochemistry from Lake Anterne sediments (North French Alps)

A high-resolution sedimentological and geochemical study was performed on a 20 m long core from the alpine Lake Anterne (2063 m a.s.l., NW French Alps) spanning the last 10 ka. Sedimentation is mainly of minerogenic origin. The organic matter quantity (TOC%) as well as its quality (hydrogen (HI) and oxygen (OI) indices) both indicate the progressive onset and subsequent stabilization of vegetation cover in the catchment from 9950 to 5550 cal. BP. During this phase, the pedogenic process of carbonate dissolution is marked by a decrease in the calcium content in the sediment record. Between 7850 and 5550 cal. BP, very low manganese concentrations suggest anoxic conditions in the bottom-water of Lake Anterne. These are caused by a relatively high organic matter (terrestrial and lacustrine) content, a low flood frequency and longer summer stratification triggered by warmer conditions. From 5550 cal. BP, a decrease in TOC, stabilization of HI and higher sedimentation rates together reflect increased erosion rates of leptosols and developed soils, probably due to a colder and wetter climate. Then, three periods of important soil destabilization are marked by an increased frequency and thickness of flood deposits during the Bronze Age and by increases in topsoil erosion relative to leptosols (HI increases) during the late Iron Age/Roman period and the Medieval periods. These periods are also characterized by higher sedimentation rates. According to palynological data, human impact (deforestation and/or pasturing activity) probably triggered these periods of increased soil erosion.