Olive (Olea europaea L.) was one of the most important fruit trees in the ancient Mediterranean region and a founder species of horticulture in the Mediterranean Basin. Different views have been ...expressed regarding the geographical origins and timing of olive cultivation. Since genetic studies and macro-botanical remains point in different directions, we turn to another proxy – the palynological evidence. This study uses pollen records to shed new light on the history of olive cultivation and large-scale olive management. We employ a fossil pollen dataset composed of high-resolution pollen records obtained across the Mediterranean Basin covering most of the Holocene. Human activity is indicated when Olea pollen percentages rise fairly suddenly, are not accompanied by an increase of other Mediterranean sclerophyllous trees, and when the rise occurs in combination with consistent archaeological and archaeobotanical evidence. Based on these criteria, our results show that the southern Levant served as the locus of primary olive cultivation as early as ~6500 years BP (yBP), and that a later, early/mid 6th millennium BP cultivation process occurred in the Aegean (Crete) – whether as an independent large-scale management event or as a result of knowledge and/or seedling transfer from the southern Levant. Thus, the early management of olive trees corresponds to the establishment of the Mediterranean village economy and the completion of the ‘secondary products revolution’, rather than urbanization or state formation. From these two areas of origin, the southern Levant and the Aegean olive cultivation spread across the Mediterranean, with the beginning of olive horticulture in the northern Levant dated to ~4800 yBP. In Anatolia, large-scale olive horticulture was palynologically recorded by ~3200 yBP, in mainland Italy at ~3400 yBP, and in the Iberian Peninsula at mid/late 3rd millennium BP.
Long-term perspective on wildfires in the western USA Marlon, Jennifer R; Bartlein, Patrick J; Gavin, Daniel G ...
Proceedings of the National Academy of Sciences,
02/2012, Letnik:
109, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Understanding the causes and consequences of wildfires in forests of the western United States requires integrated information about fire, climate changes, and human activity on multiple temporal ...scales. We use sedimentary charcoal accumulation rates to construct long-term variations in fire during the past 3,000 y in the American West and compare this record to independent fire-history data from historical records and fire scars. There has been a slight decline in burning over the past 3,000 y, with the lowest levels attained during the 20th century and during the Little Ice Age (LIA, ca. 1400–1700 CE Common Era). Prominent peaks in forest fires occurred during the Medieval Climate Anomaly (ca. 950–1250 CE) and during the 1800s. Analysis of climate reconstructions beginning from 500 CE and population data show that temperature and drought predict changes in biomass burning up to the late 1800s CE. Since the late 1800s , human activities and the ecological effects of recent high fire activity caused a large, abrupt decline in burning similar to the LIA fire decline. Consequently, there is now a forest "fire deficit" in the western United States attributable to the combined effects of human activities, ecological, and climate changes. Large fires in the late 20th and 21st century fires have begun to address the fire deficit, but it is continuing to grow.
In the Mediterranean region, Corsica represents one of the most important hotspots of biodiversity, partly due to the high number of endemics species. This region is also one of the most affected by ...forest fires worldwide. The present vegetation is adapted to a wide range of disturbance regimes, but a change in fire frequency or intensity in the future may severely affect ecological resources and other socio-economical aspects. Here, we study the dynamics of vegetation–human–fire interactions for the past 12,000 years as recorded by Lake Bastani (Corsica, France). We used well-dated sedimentary records of charcoal, pollen and fungal spores to infer past fire regime, land cover and pastoral activities, respectively, and we compared our results with charcoal records from two other Corsican lakes (Nino and Creno, respectively). Our results suggest that climate and natural fires were the main factors shaping the landscape before 5000 cal. BP. Then, the extraordinary diversity of the current Corsican vegetation has been mainly promoted by human activities on the island (i.e. deforestation and pastoralism) at least from the Bronze Age (3500 cal. BP). The top of our record shows a sharp decrease in fungal remains (Sporormiella-type), usually associated with pastoral activities, which could be attributed to the land abandonment occurring since a few decades.
The study of fire history and driving mechanisms at long time scales can provide a theoretical background for future fire management in forested regions. The alpine lake sediments from Daye Lake in ...the Qinling Mountains, east‐central China, were used to explore the influence of climate, vegetation and human activity on fires since the LGM, based on charcoals and black carbon. During the last glacial period, fire activity was mostly controlled by regional aridity under a weak East Asian summer monsoon, while human‐induced fires were commonly dominated in the late Holocene. Fire activity was found to be linked to biomass through temperature variability. The biofuel dominated by conifers induced high intensity fires in the last glacial, and herbs contributed more to the high fire frequency over the mid‐late Holocene. With predicted future rising temperatures, increased vegetation cover and extreme climate events may increase the fire risk in the region.
Plain Language Summary
Fire activity has an important influence on climate changes and carbon cycling. Understanding past fire history and its driving mechanisms are essential to mitigate the impact of fires. Here, we present fire records from alpine lake sediments in the Qinling Mountains since the LGM. Results indicate that climatological drought under a prevailing weak East Asian summer monsoon increased fire activity during 21.6–11.7 cal ka BP, while human‐induced fires became more common in the late Holocene due to land use, for example, the forest clearing for agriculture and the warfare. And high temperature increases fuel loads, resulting in more fires. Moreover, vegetation types with varying biofuel supply also influence fire activity. We suggest that fire risk may increase in the region with future rising temperature. Our results have implications for understanding fire history and management in other transitional vegetation zones globally.
Key Points
The prevailing weak East Asian summer monsoon mostly controlled fire activity during the last glacial, whilst human activity became common through the Holocene
The conifers induced high intensity fires in the last glacial and herbs contributed more to high fire frequency over the mid‐late Holocene
Forest resources in east‐central China will face the increased fire risks in the context of global warming and increasing vegetation cover
Fire regime changes are considered a major threat to future biodiversity in the Mediterranean Basin. Such predictions remain uncertain, given that fire regime changes and their ecological impacts ...occur over timescales that are too long for direct observation. Here we analyse centennial- and millennial-scale shifts in fire regimes and compositional turnover to track the consequences of fire regime shifts on Mediterranean vegetation diversity. We estimated rate-of-change, richness and compositional turnover (beta diversity) in 13 selected high-resolution palaeoecological records from Mediterranean Iberia and compared these with charcoal-inferred fire regime changes. Event sequence analysis showed fire regime shifts to be significantly temporally associated with compositional turnover, particularly during the last three millennia. We find that the timing and direction of fire and diversity change in Mediterranean Iberia are best explained by long-term human–environment interactions dating back perhaps 7500 years. Evidence suggests that Neolithic burning propagated a first wave of increasing vegetation openness and promoted woodland diversity around early farming settlements. Landscape transformation intensified around 5500 to 5000 cal. yr BP and accelerated during the last two millennia, as fire led to permanent transitions in ecosystem state. These fire episodes increased open vegetation diversity, decreased woodland diversity and significantly altered richness on a regional scale. Our study suggests that anthropogenic fires played a primary role in diversity changes in Mediterranean Iberia. Their millennia-long legacy in today’s vegetation should be considered for biodiversity conservation and landscape management.
Fire is a primary mode of natural disturbance in the forests of the Pacific Northwest. Increased fuel loads following fire suppression and the occurrence of several large and severe fires have led to ...the perception that in many areas there is a greatly increased risk of high-severity fire compared with presettlement forests. To reconstruct the variability of the fire regime in the Siskiyou Mountains, Oregon, we analyzed a 10-m, 2,000-y sediment core for charcoal, pollen, and sedimentological data. The record reveals a highly episodic pattern of fire in which 77% of the 68 charcoal peaks before Euro-American settlement cluster within nine distinct periods marked by a 15-y mean interval. The 11 largest charcoal peaks are significantly related to decadal-scale drought periods and are followed by pulses of minerogenic sediment suggestive of rapid sediment delivery. After logging in the 1950s, sediment load was increased fourfold compared with that from the most severe presettlement fire. Less severe fires, marked by smaller charcoal peaks and no sediment pulses, are not correlated significantly with drought periods. Pollen indicators of closed forests are consistent with fire-free periods of sufficient length to maintain dense forest and indicate a fire-triggered switch to more open conditions during the Medieval Climatic Anomaly. Our results indicate that over millennia fire was more episodic than revealed by nearby shorter tree-ring records and that recent severe fires have precedents during earlier drought episodes but also that sediment loads resulting from logging and road building have no precedent in earlier fire events.
1 A Holocene sedimentary sequence from a coastal lake in the Mediterranean area (Lago di Massaciuccoli, Tuscany, Italy, 0 m a.s.l.) was sampled for pollen and microscopic charcoal analyses. ...Contiguous 1-cm samples represent an estimated time interval of c. 13 years, thus providing a high-resolution sequence from 6100 to 5400 cal. years bp. 2 Just before 6000 cal. years bp, sub-Mediterranean and Mediterranean forests were present together with fir (Abies alba), a submontane species that is today absent at low altitudes in the Mediterranean. A sharp vegetational change occurred after 6000 cal. years bp involving a drastic decline of Abies alba around the site. 3 Time-series analyses suggest that increased fire activity at this time caused a strong decline in Abies alba, a highly fire-sensitive species. During 100 years of higher fire incidence, diverse (predominantly evergreen) forest communities were converted to low-diversity fire-prone shrub communities. 4 Cross-correlations reveal that fire during the mid-Holocene hindered the expansion of holm oak (Quercus ilex), the most common tree species today in Mediterranean environments. While the factors that triggered the Holocene expansion of this species in the Mediterranean area are unclear, our results do not support the hypothesis that fire was key for holm oak expansion. 5 Diatom analyses of the same sediment core provide an independent palaeoenvironmental proxy for palaeoclimatic reconstruction. A change in the eutrophy and salinity of the lake occurred just before 6000 cal. years bp, suggesting that a climatic shift towards aridity may have triggered the observed change in hydrology and possibly also in fire regime. 6 Over the millennia fire has decisively contributed to the establishment of the present fire-adapted vegetation type (macchia). Native fire-sensitive species were displaced or repressed, and arboreal vegetation became less diverse. Combined ecological and palaeoecological data may help to assess possible future scenarios of biosphere responses to global change. Our results imply that the forecasted global warming and fire increase may trigger irrecoverable biodiversity losses and shifts in vegetational composition within a few decades or centuries at most. In particular, fire and drought-sensitive vegetation types, such as the relict forests of Abies alba in the Apennines, seem particularly threatened by large-scale displacement.
Aim: We provide the first European-scale geospatial training set relating the charcoal signal in surface lake sediments to fire parameters (number, intensity and area) recorded by satellite moderate ...resolution imaging spectroradiometer (MODIS) sensors. Our calibration is intended for quantitative reconstructions of key fire-regime parameters by using sediment sequences of microscopic (MIC from pollen slides, particles 10–500 μm) and macroscopic charcoal (MAC from sieves, particles > 100 μm). Location: North–south and east–west transects across Europe, covering the mediterranean, temperate, alpine, boreal and steppe biomes. Time period: Lake sediments and MODIS active fire and burned area products were collected for the years 2012–2015. Methods: Cylinder sediment traps were installed in lakes to annually collect charcoal particles in sediments. We quantitatively assessed the relationships between MIC and MAC influx (particles/cm2/year) and the MODIS-derived products to identify source areas of charcoal and the extent to which lake-sediment charcoal is linked to fire parameters across the continent. Results: Source area of sedimentary charcoal was estimated to a 40-km radius around sites for both MIC and MAC particles. Fires occurred in grasslands and in forests, with grass morphotypes of MAC accurately reflecting the burned fuel-type. Despite the lack of local fires around the sites, MAC influx levels reached those reported for local fires. Both MIC and MAC showed strong and highly significant relationships with the MODIS-derived fire parameters, as well as with climatic variation along a latitudinal temperature gradient. Main conclusions: MIC and MAC are suited to quantitatively reconstructing fire number and fire intensity on a regional scale. However, burned area may only be estimated using MAC. Local fires may be identified by using several lines of evidence, e.g. analysis of large particles (> 600 μm), magnetic susceptibility and sedimentological data. Our results offer new insights and applications to quantitatively reconstruct fires and to interpret available sedimentary charcoal records.
Mediterranean rear-edge populations of Betula, located at the southwestern Eurasian margin of the distribution range, represent unique reservoirs of genetic diversity. However, increasing densities ...of wild ungulates, enhanced dryness, and wildfires threaten their future persistence. A historical perspective on the past responses of these relict populations to changing herbivory, fire occurrence and climatic conditions may contribute to assessing their future responses under comparable scenarios. We have reconstructed vegetation and disturbance (grazing, fire) history in the Cabañeros National Park (central-southern Spain) using the paleoecological records of two small mires. We particularly focused on the historical range of variation in disturbance regimes, and the dynamics of rear-edge Betula populations and herbivore densities. Changes in water availability, probably related to the North Atlantic Oscillation (NAO) index, and land-use history have played a crucial role in vegetation shifts. Our data suggest that heathlands (mainly Erica arborea and E. scoparia) and Quercus woodlands dominated during dry phases while Sphagnum bogs and Betula stands expanded during wet periods. Betula populations survived past moderately dry periods but were unable to cope with enhanced land use, particularly increasing livestock raising since ~1,100–900 cal. yr BP (850–1,050 CE), and eventually underwent local extinction. High herbivore densities not only contributed to the Betula demise but also caused the retreat of Sphagnum bogs. Ungulate densities further rose at ~200–100 cal. yr BP (1750–1850 CE) associated with the historically documented intensification of land use around the Ecclesiastical Confiscation. However, herbivory reached truly unprecedented values only during the last decades, following rural depopulation and subsequent promotion of big game hunting. For the first time in temperate and Mediterranean Europe, we have used the abundances of fossil dung fungal spores to assess quantitatively that current high herbivore densities exceed the historical range of variation. In contrast, present fire activity lies within the range of variation of the last millennia, with fires (mainly human-set) mostly occurring during dry periods. Our paleodata highlight the need of controlling the densities of wild ungulates to preserve ecosystem composition and functioning. We also urge to restore Betula populations in suitable habitats where they mostly disappeared because of excessive human activities.
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