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1.
We show how sedimentary charcoal records from multiple sites within a single landscape can be used to compare fire histories and reveal small scale patterns in fire regimes. Our objective is to develop strategies for classifying and comparing late-Holocene charcoal records in Midwestern oak- and pine-dominated sand plain ecosystems where fire regimes include a mix of surface and crown fires. Using standard techniques for the analysis of charcoal from lake sediments, we compiled 1000- to 4000-yr-long records of charcoal accumulation and charcoal peak frequencies from 10 small lakes across a sand plain in northwestern Wisconsin. We used cluster analysis to identify six types of charcoal signatures that differ in their charcoal influx rates, amount of grass charcoal, and frequency and magnitude of charcoal peaks. The charcoal records demonstrate that while fire histories vary among sites, there are regional patterns in the occurrence of charcoal signature types that are consistent with expected differences in fire regimes based on regional climate and vegetation reconstructions. The fire histories also show periods of regional change in charcoal signatures occurring during times of regional climate changes at ~ 700, 1000, and 3500 cal yr BP.  相似文献   

2.
Microscopic charcoal from varved Santa Barbara Basin sediments was used to reconstruct a 560-yr record (A.D. 1425 to 1985) of Santa Ana fires. Comparison of large (>3750 μm2) charcoal with documented fire records in the Santa Barbara Ranger District shows that high accumulations correspond to large fires (>20,000 ha) that occurred during Santa Ana conditions. The charcoal record reconstructed a minimum of 20 large fires in the Santa Barbara region during the study period. The average time between fires shows no distinct change across three different land use periods: the Chumash period, apparently characterized by frequent burning, the Spanish/Early American period with nominal fire control, and the 20th century with active fire suppression. Pollen data support the conclusion that the fire regime has not dramatically changed during the last 500 yr. Comparison of large charcoal particle accumulation rates and precipitation reconstructed from tree rings show a strong relationship between climate and fire history, with large fires consistently occurring at the end of wet periods and the beginning of droughts.  相似文献   

3.
A high‐resolution, multiproxy record encompassing the last glacial–interglacial transition is presented for Native Companion Lagoon, a coastal site in subtropical eastern Australia. Rates of aeolian sedimentation in the lake were established by trace element analyses of lacustrine sediments and used as a proxy for aridity. In conjunction with sediment moisture content, charcoal and pollen these provide a multi‐decadal record of palaeoenvironmental variability for the period 33–18 k cal. yr BP. Results indicate that the Last Glacial Maximum in eastern Australia spanned almost 10 k cal. yr, and was characterised by two distinct cold dry events at approximately 30.8 k cal. yr BP and 21.7 k cal. yr BP. Provenance of selected sediment samples by trace element geochemical fingerprinting shows that continental sourced aeolian sediments originated primarily from South Australia during these cold events and from sites in central Australia during the intervening time. Used in combination with a pollen record, the provenance of long‐travelled dust to mainland sites shows that the two cold events were characterised by frequent meridional dry southwesterly winds rather than zonal westerly airflow as previously believed. The intervening period was cool and humid, which we infer as being associated with more frequent southeasterly winds of maritime origin. These results lend support to previous research that indicates the Southern Hemisphere experienced a period of widespread climatic amelioration at the height of the last glacial known as the Antarctic Isotopic Maximum. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

4.
Previously only three terrestrial interglacial periods were known from southern Scandinavia, all of which could be relatively easily correlated within the central European stratigraphical framework. Here, we present a new interglacial–interstadial pollen, plant macrofossil and charcoal record from Trelde Klint, Denmark, and analyse its biostratigraphy, correlation with other European records, vegetation development, fire dynamics and absolute dating. Except for a slight truncation of the early part of the record, the pollen stratigraphy exhibits a full interglacial succession, including temperate trees (Quercus, Ulmus and Tilia) during its mesocratic stage. Macrofossil analysis allowed identification to species level for Quercus robur, Picea abies and two mosses. Conifers (Pinus and Picea) dominate the pollen record of the interglacial sequence, and the occurrence of Larix pollen in the top part of the interglacial record as well as in the interstadial sediments is especially indicative of this interglacial. The overall diversity of tree genera is rather low. These biostratigraphical features suggest that Trelde Klint is unique among Danish records, but it is similar to records from northern Germany. Numerical analyses (REVEALS and DCA) indicate that forests during the temperate stage were dense and that vegetation openness increased only towards the end of the interglacial, accompanied by increased fire occurrence. A short interstadial sequence with a dominance of Pinus and Betula and the presence of Larix is present above the interglacial deposit. We argue that lack of attention to differences in fire regimes may hamper understanding of between‐site correlations of interglacial pollen records. OSL dating, using a novel feldspar technique, yields an average age of 350±20 ka for the sandy sediments above the interglacial layers at Trelde Klint, suggesting that the whole interglacial–interstadial succession belongs to Marine Isotope Stage 11.  相似文献   

5.
High-resolution charcoal and pollen analyses were used to reconstruct a 12,000-yr-long fire and vegetation history of the Tumalo Lake watershed and to examine the short-term effects that tephra deposition have on forest composition and fire regime. The record suggests that, from 12,000 to 9200 cal yr BP, the watershed was dominated by an open Pinus forest with Artemisia as a common understory species. Fire episodes occurred on average every 115 yr. Beginning around 9200 cal yr BP, and continuing to the present, Abies became more common while Artemisia declined, suggesting the development of a closed forest structure and a decrease in the frequency of fire episodes, occurring on average every 160 yr. High-resolution pollen analyses before and after the emplacement of three distinct tephra deposits in the watershed suggest that nonarboreal species were most affected by tephra events and that recovery of the vegetation community to previous conditions took between 40 and 100 yr. Changes in forest composition were not associated with tephra depositional events or changes in fire-episode frequency, implying that the regional climate is the more important control on long-term forest composition and structure of the vegetation in the Cascade Range.  相似文献   

6.
We have compiled 223 sedimentary charcoal records from Australasia in order to examine the temporal and spatial variability of fire regimes during the Late Quaternary. While some of these records cover more than a full glacial cycle, here we focus on the last 70,000 years when the number of individual records in the compilation allows more robust conclusions. On orbital time scales, fire in Australasia predominantly reflects climate, with colder periods characterized by less and warmer intervals by more biomass burning. The composite record for the region also shows considerable millennial-scale variability during the last glacial interval (73.5–14.7 ka). Within the limits of the dating uncertainties of individual records, the variability shown by the composite charcoal record is more similar to the form, number and timing of Dansgaard–Oeschger cycles as observed in Greenland ice cores than to the variability expressed in the Antarctic ice-core record. The composite charcoal record suggests increased biomass burning in the Australasian region during Greenland Interstadials and reduced burning during Greenland Stadials. Millennial-scale variability is characteristic of the composite record of the sub-tropical high pressure belt during the past 21 ka, but the tropics show a somewhat simpler pattern of variability with major peaks in biomass burning around 15 ka and 8 ka. There is no distinct change in fire regime corresponding to the arrival of humans in Australia at 50 ± 10 ka and no correlation between archaeological evidence of increased human activity during the past 40 ka and the history of biomass burning. However, changes in biomass burning in the last 200 years may have been exacerbated or influenced by humans.  相似文献   

7.
In this study, we synthesized the fossil pollen data from 10 lake sediments and 2 land cores to integrate the alteration of forest covered areas in northern Taiwan with changes in humidity and temperature over the last 2000 years. The abundance of arboreal pollen, fern spores and Tsuga pollen in the pollen and spore assemblages were used as indicators. Our results suggested that the climate in northern Taiwan was stably cool and dry during 2000–1000 cal. yr BP, but changed to wet and warm during 1000–500 cal. yr BP, which corresponded to the Medieval Warm Period (MWP). In addition, an increased density and dispersal of Tsuga pollen corresponding to 500–200 cal. yr BP was observed, which corresponded to the Little Ice Age (LIA). In recent years, a decline in Tsuga pollen density and increased fern spore density has been observed, which indicates an increase in temperature associated with elevated rainfall. Based on the synthesized data set, we conducted GIS mapping of such changes in the north of Taiwan over time. The results revealed that the temporal and spatial climate changes could be inferred from the palynological GIS mapping method, and that the fluctuations in temperature over time matched well with the global climate events, including MWP, LIA and recent warming.  相似文献   

8.
We reconstructed a 10,500-yr fire and vegetation history of a montane site in the North Cascade Range, Washington State based on lake sediment charcoal, macrofossil and pollen records. High-resolution sampling and abundant macrofossils made it possible to analyze relationships between fire and vegetation. During the early Holocene (> 10,500 to ca. 8000 cal yr BP) forests were subalpine woodlands dominated by Pinus contorta. Around 8000 cal yr BP, P. contorta sharply declined in the macrofossil record. Shade tolerant, mesic species first appeared ca. 4500 cal yr BP. Cupressus nootkatensis appeared most recently at 2000 cal yr BP. Fire frequency varies throughout the record, with significantly shorter mean fire return intervals in the early Holocene than the mid and late Holocene. Charcoal peaks are significantly correlated with an initial increase in macrofossil accumulation rates followed by a decrease, likely corresponding to tree mortality following fire. Climate appears to be a key driver in vegetation and fire regimes over millennial time scales. Fire and other disturbances altered forest vegetation at shorter time scales, and vegetation may have mediated local fire regimes. For example, dominance of P. contorta in the early Holocene forests may have been reinforced by its susceptibility to frequent, stand-replacing fire events.  相似文献   

9.
Lynch's Crater preserves a continuous, high‐resolution record of environmental changes in north Queensland. This record suggests a marked increase in burning that appears to be independent of any known major climatic boundaries. This increase is accompanied, or closely followed, by the virtually complete replacement of rainforest by sclerophyll vegetation. The absence of any major climatic shift associated with this increase in fire frequency therefore has been interpreted as a result of early human impact in the area. The age for this increase in burning, on the basis of conventional radiocarbon dating, was previously thought to be approximately 38 000 14C yr BP, supporting the traditional model for human arrival in Australia at 40 000 14C yr BP Here we have applied a more rigorous pre‐treatment and graphitisation procedure for radiocarbon dating samples from the Lynch's Crater sequence. These new dates suggest that the increase in fire frequency occurred at 45 000 14C yr BP, supporting the alternative view that human occupation of Australia occurred by at least 45 000–55 000 cal. yr BP. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

10.
A new extended pollen and charcoal record is presented from Lake Euramoo, Wet Tropics World Heritage rainforest of northeast Queensland, Australia. The 8.4-m sediment core taken from the center of Lake Euramoo incorporates a complete record of vegetation change and fire history spanning the period from 23,000 cal yr B.P. to present. The pollen record is divided into five significant zones; 23,000–16,800 cal yr B.P., dry sclerophyll woodland; 16,800–8600 cal yr B.P., wet sclerophyll woodland with marginal rainforest in protected pockets; 8600–5000 cal yr B.P., warm temperate rainforest; 5000–70 cal yr B.P., dry subtropical rainforest; 70 cal yr B.P.–AD 1999, degraded dry subtropical rainforest with increasing influence of invasive species and fire.The process of rainforest development appears to be at least partly controlled by orbital forcing (precession), though more local environmental variables and human activity are also significant factors. This new record provides the opportunity to explore the relationship between fire, drought and rainforest dynamics in a significant World Heritage rainforest region.  相似文献   

11.
A 2000-year accumulation of varved sediments from Hell's Kitchen Lake in north-central Wisconsin was analyzed for pollen, charcoal, and seeds. The varves provided an accurate time scale for the study. The pollen record indicates changes on two different time scales. Short-term changes lasting several decades appear to be superimposed on long-term changes lasting several centuries. The short-term changes are related to individual fires, and the long-term changes result from increases or decreases in the frequency of these perturbations. From 2000 to 1150 years ago the average interval between fires was about 100 years, and from 1150 to 120 years ago the interval increased to about 140 years. Evidence from pollen, seeds, and charcoal at Hell's Kitchen Lake suggests that at least two “moist” intervals occurred during the past 2000 years, one between 2000 and 1700 years ago and the other between 600 and 100 years ago. A third but minor “moist” period occurred about 1150 to 850 years ago. A pollen and seed diagram shows that these intervals are characterized by increased percentages of white pine pollen, hemlock pollen, and yellow birch seeds, and by decreased levels of charcoal. The “dry” interval of 1700 to 1150 years ago is characterized by increased percentages of paper birch seeds, oak pollen, and aspen pollen, along with high levels of charcoal. The times of climatic change indicated at Hell's Kitchen Lake are nearly synchronous with those based on studies of tree rings, soils, glacial activity, and other pollen studies from various regions of North America, but the direction of these inferred changes is not always the same. This result suggests that the long-wave pattern of the general circulation has been variable during the past 2000 years.  相似文献   

12.
《Quaternary Science Reviews》2007,26(19-21):2631-2643
In order to link the charcoal record from sedimentary archives with the combustion processes that reflect past anthropogenic activity, a novel method based on automated image analysis was developed. It allows a detailed quantification and morphological analysis of the combustion-derived products that were emitted in the area of Lake Lucerne (Central Europe) throughout the last 7200 years.Charcoal-particle distribution reconstructed from the composite sedimentary record shows that the charcoal input is primarily linked to redistribution of detrital μm-size charcoal degradation products from surface runoff into the large lake basin. However, the independent distribution of the coarser charcoal fraction (>38 μm) exhibits four major periods of large-scale fire activity around 5500, 3300, 2400, and 530 cal. BP. These events are synchronous with major anthropogenic changes (lake-dwellings, land-use changes, technological innovations), although it is possible that these major fire episodes could have been indirectly triggered by climatic deterioration and unfavorable environmental conditions. During the late-nineteenth-century, a great increase in slag particles and magnetic spherules of fly-ash occurred due to the steamboat navigation on Lake Lucerne. The successive burning of wood (after AD 1838), coal (after AD 1862), and diesel (after AD 1931) by the steamboat traffic produced specific particle shapes, providing valuable chronological markers for dating the recent sediments and a proxy for fossil fuel combustion.  相似文献   

13.
A combined pollen, charcoal and climatic record is presented from Cranes Moor, southern England, covering the period c. 10 500–5850 cal a BP. It is shown that the occurrence of burning is closely related to natural processes, including prevailing climatic conditions and vegetation composition. These burning events are often linked to an increase in the summer moisture deficit, implying that the timing of burning events is linked to periods of warmer/drier climate during the Holocene Thermal Maximum (c. 11 000–5000 cal a BP). These events play an important role in the vegetation composition and succession around the site. The nature of the burning recorded at the site shows strong similarities with other records from northern Europe. This study throws caution on suggestions that fire in the Holocene record from areas such as the British Isles is linked only to human activity, and enhances the possibility that natural fire incidence played an important role in natural woodland structure dynamics.  相似文献   

14.
Charcoal particles are widespread in terrestrial and lake environments of the northern temperate and boreal biomes where they are used to reconstruct past fire events and regimes. In this study, we used botanically identified and radiocarbon-dated charcoal macrofossils in mineral soils as a paleoecological tool to reconstruct past fire activity at the stand scale. Charcoal macrofossils buried in podzolic soils by tree uprooting were analyzed to reconstruct the long-term fire history of an old-growth deciduous forest in southern Québec. Charcoal fragments were sampled from the uppermost mineral soil horizons and identified based on anatomical characters. Spruce (Picea spp.) fragments dominated the charcoal assemblage, along with relatively abundant wood fragments of sugar maple (Acer saccharum) and birch (Betula spp.), and rare fragments of pine (Pinus cf. strobus) and white cedar (Thuja canadensis). AMS radiocarbon dates from 16 charcoal fragments indicated that forest fires were widespread during the early Holocene, whereas no fires were recorded from the mid-Holocene to present. The paucity of charcoal data during this period, however, does not preclude that a fire event of lower severity may have occurred. At least eight forest fires occurred at the study site between 10,400 and 6300 cal yr B.P., with a dominance of burned conifer trees between 10,400 and 9000 cal yr B.P. and burned conifer and deciduous trees between 9000 and 6300 cal yr B.P. Based on the charcoal record, the climate at the study site was relatively dry during the early Holocene, and more humid from 6300 cal yr B.P. to present. However, it is also possible that the predominance of conifer trees in the charcoal record between 10,400 and 6300 cal yr B.P. created propitious conditions for fire spreading. The charcoal record supports inferences based on pollen influx data (Labelle, C., Richard, P.J.H. 1981. Végétation tardiglaciaire et postglaciaire au sud-est du Parc des Laurentides, Québec. Géographie Physique et Quaternaire 35, 345-359) of the early arrival of spruce and sugar maple in the study area shortly after deglaciation. We conclude that macroscopic charcoal analysis of mineral soils subjected to disturbance by tree uprooting may be a useful paleoecological tool to reconstruct long-term forest fire history at the stand scale.  相似文献   

15.
Analyses of pollen, charcoal and organic content in a lake sediment core from Wildwood Lake, Long Island, New York, provide insights into the ecological and environmental history of this region. The early Holocene interval of the record (ca. 9800–8800 cal. a BP) indicates the presence of Pinus rigida–Quercus ilicifolia woodlands with high fire activity. A layer of sandy sediment dating to 9200 cal. a BP may reflect a brief period of reduced water depth, consistent with widespread evidence for cold, dry conditions at that time. Two other sandy layers, bracketed by 14C dates, represent a sedimentary hiatus from ca. 8800 to 4500 cal. a BP. This discontinuity may reflect the removal of some sediment during brief periods of reduced water depth at 5300 and 4600 cal. a BP. In the upper portion of the record (<4500 cal. a BP), subtle changes at ca. 3000 cal. a BP indicate declining prevalence of Quercus–Fagus–Carya forests and increasing abundance of Pinus rigida, perhaps due to reduced summer precipitation. Elevated percentages of herbaceous taxa in the uppermost sediments represent European agricultural activities. However, unlike charcoal records from southern New England, fire activity does not increase dramatically with European settlement. These findings indicate that present‐day Pinus rigida–Quercus ilicifolia woodlands on eastern Long Island are not a legacy of recent, anthropogenic disturbances. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

16.
Paleoenvironments of the Torrey Pines State Reserve were reconstructed from a 3600-yr core from Los Peñasquitos Lagoon using fossil pollen, spores, charcoal, chemical stratigraphy, particle size, and magnetic susceptibility. Late Holocene sediments were radiocarbon dated, while the historical sediments were dated using sediment chemistry, fossil pollen, and historical records. At 3600 yr B.P., the estuary was a brackish-water lagoon. By 2800 yr B.P., Poaceae (grass) pollen increased to high levels, suggesting that the rising level of the core site led to its colonization by Spartina foliosa (cord-grass), the lowest-elevation plant type within regional estuaries. An increase in pollen and spores of moisture-dependent species suggests a climate with more available moisture after 2600 yr B.P. This change is similar to that found 280 km to the north at 3250 yr B.P., implying that regional climate changes were time-transgressive from north to south. Increased postsettlement sediment input resulted from nineteenth-century land disturbances caused by grazing and fire. Sedimentation rates increased further in the twentieth century due to closure of the estuarine mouth. The endemic Pinus torreyana (Torrey pine) was present at the site throughout this 3600-yr interval but was less numerous prior to 2100 yr B.P. This history may have contributed to the low genetic diversity of this species.  相似文献   

17.
A 3.5-m-long sediment sequence from a lake on Raffles Ø, off Liverpool Land, East Greenland, was investigated for chronology, lithology, palynology and biogeochemistry. Radiocarbon-dating of plant remains and the lithology of the sediment succession indicate continuous sedimentation since deglaciation of the area prior to 10000 cal. yr BP. The postglacial palynological record shows little variation and evidence of a wind-transported pollen supply, both resulting from the geographical characteristics of Raffles Ø. Significant variations in the biogeochemical data reflect changes in aquatic bioproduction. These changes depend to some extent on climatic changes; however, they are mainly due to variations in seabird breeding colonies in the catchment which influence nutrient and cadmium supply to the lake. Large seabird breeding colonies were present between 7500 and 1900, from 1000 to 500, and since c. 100 cal. yr BP. Their absence prior to 7500 cal. yr BP may be the result of unsuitable feeding conditions close to Raffles Ø caused by a too dense or too open sea-ice cover. In contrast, between 1900 and 1000 and from 500 to 100 cal. yr BP, the seabird settlement was probably restricted by an insufficiently long breeding season due to cold climate conditions in East Greenland.  相似文献   

18.
Holocene fire-climate-vegetation linkages are mostly understood at individual sites by comparing charcoal and pollen records with other paleoenvironmental proxy and model simulations. This scale of reconstruction often obscures detection of large-scale patterns in past fire activity that are related to changes in regional climate and vegetation. A network of 31 charcoal records from southern South America was examined to assess fire history along a transect from subtropic to subantarctic biomes. The charcoal data indicate that fire activity was greater than present at ca. 12,000 cal yr BP and increased further and was widespread at 9500 cal yr BP. Fire activity decreased and became more spatially variable by 6000 cal yr BP, and this trend continued to present. Atmospheric circulation anomalies during recent high-fire years show a southward shift in westerlies, and paleoclimate model simulations and data syntheses suggest that such conditions may have prevailed for millennia in the early Holocene when the pole-to-equator temperature gradients were weaker and annual temperatures were higher than present, in response to orbital-time-scale insolation changes.  相似文献   

19.
We compare high-resolution pollen and chironomid records from the last 15,000 yr in Laguna Facil, southern Chile. Major vegetation and chironomid changes are recorded between ca 14,900 and 14,700 cal. yr BP. During the Lateglacial, changes in the chironomid stratigraphy lag behind changes in the pollen stratigraphy suggesting that the chironomids are responding to changes in the tree canopy or in soil chemistry brought about by vegetational development. At about 7200 cal. yr BP there is a change in the chironomid stratigraphy in advance of changes in the vegetation. This suggests that the response is to regional climatic change. The relatively close correlation of the chironomid and pollen stratigraphies with changes in charcoal concentrations also implicates the importance of fire and/or vulcanism in influencing the dynamics of forest and limnological systems. There is no clear evidence of cooling during the Younger Dryas chronozone in Laguna Facil.  相似文献   

20.
Here, we present two high-resolution records of macroscopic charcoal from high-elevation lake sites in the Sierra Nevada, California, and evaluate the synchroneity of fire response for east- and west-side subalpine forests during the past 9200 yr. Charcoal influx was low between 11,200 and 8000 cal yr BP when vegetation consisted of sparse Pinus-dominated forest and montane chaparral shrubs. High charcoal influx after ∼ 8000 cal yr BP marks the arrival of Tsuga mertensiana and Abies magnifica, and a higher-than-present treeline that persisted into the mid-Holocene. Coeval decreases in fire episode frequency coincide with neoglacial advances and lower treeline in the Sierra Nevada after 3800 cal yr BP. Independent fire response occurs between 9200 and 5000 cal yr BP, and significant synchrony at 100- to 1000-yr timescales emerges between 5000 cal yr BP and the present, especially during the last 2500 yr. Indistinguishable fire-return interval distributions and synchronous fires show that climatic control of fire became increasingly important during the late Holocene. Fires after 1200 cal yr BP are often synchronous and corroborate with inferred droughts. Holocene fire activity in the high Sierra Nevada is driven by changes in climate linked to insolation and appears to be sensitive to the dynamics of the El Niño-Southern Oscillation.  相似文献   

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