The representation of rainfall and fire intensity in fossil pollen and charcoal records from a South African savanna

Savanna ecosystems of southern Africa are strongly influenced by water availability and fire intensity, and this study aimed to show whether these two specific environmental variables are reflected in fossil pollen and charcoal records. Palaeoecological records of charcoal concentration from three short sedimentary sequences were used to reconstruct fire intensity (the rate of energy released along a fire front) over 50 yrs in the Kruger National Park (KNP), South Africa. Fossil pollen percentages from surface and core-sediment samples taken from water bodies were compared with the reconstructed fire intensity over space and time. Higher fire intensity led to increased herbaceous cover and decreased woody plant growth. Fossil pollen percentages and charcoal concentrations were also compared with rainfall records. Increased macroscopic charcoal abundances and percentages of Cyperaceae pollen corresponded to periods of increased rainfall. The results of this study have shown that fossil pollen and charcoal records from savanna environments can be used to reconstruct past fire intensity and its impact on terrestrial vegetation, as well as changes in rainfall.     

Vegetation and fire history of a Chinese site in southern tropical Xishuangbanna derived from phytolith and charcoal records from Holocene sediments

Aim The aims of this paper are to reconstruct the vegetation and fire history over the past 2000 years in a well‐preserved rain‐forest area, to understand interactions between climate, fire, and vegetation, and to predict how rain forest responds to global warming and increased intensity of human activity. Location Xishuangbanna, south‐west China, 21–22° N, 101–102° E. Methods Phytolith (plant opal silica bodies) morphotypes, assemblages, and indices were used to reconstruct palaeovegetation and palaeoclimate changes in detail. Micro‐charcoal particles found in phytolith slides, together with burnt phytoliths and highly weathered bulliform cells, were employed to reconstruct a record of past fire occurrence. A survey of field sediments, lithology, and ¹⁴C dating were also employed. Results Phytoliths were divided into 11 groups and classified into 33 well‐described morphotypes according to their shape under light microscopy and their presumed anatomical origins and ecological significance. The phytolith assemblages were divided into six significant zones that reveal a complete history of vegetation changes corresponding to climate variation and fire occurrence. Phytolith assemblages and indices show that the palaeoclimate in the study area is characterized by the alternation of warm–wet and cool–dry conditions. Phytolith and charcoal records reveal that 12 fire episodes occurred. Comparison of burnt phytoliths with an aridity index (Iph) shows that fire episodes have a strong relationship with drought events. Main conclusions Our results indicate that fire occurrence in the tropical rain forest of Xishuangbanna is predominantly under the control of natural climate variability (drought events). Nearly every fire episode is coupled with a climatic event and has triggered vegetation composition changes marked by a pronounced expansion of grasses. This indicates that drought interacts with fire to exert a strong influence on the ecological dynamics of the rain forest. However, the impact of human activity in recent centuries is also significant. Our results are important for understanding the interactions between climate, fire, and vegetation, and for predicting how rain forest responds to global warming and increased human activity.     

Does fuel type influence the amount of charcoal produced in wildfires? Implications for the fossil record

Charcoal occurrence is extensively used as a tool for understanding wildfires over geological timescales. Yet, the fossil charcoal literature to date rarely considers that fire alone is capable of creating a bias in the abundance and nature of charcoal it creates, before it even becomes incorporated into the fossil record. In this study we have used state‐of‐the‐art calorimetry to experimentally produce charcoal from 20 species that represent a range of surface fuels and growth habits, as a preliminary step towards assessing whether different fuel types (and plant organs) are equally likely to remain as charcoal post‐fire. We observe that charcoal production appears to be species specific, and is related to the intrinsic physical and chemical properties of a given fuel. Our observations therefore suggest that some taxa are likely to be overrepresented in fossil charcoal assemblages (i.e. needle‐shed conifers, tree ferns) and others poorly represented, or not preserved at all (i.e. broad shoot‐shed conifers, weedy angiosperms, shrub angiosperms, some ferns). Our study highlights the complexity of charcoal production in modern fuels and we consider what a bias in charcoal production may mean for our understanding of palaeowildfires.     

Observations of the structural changes that occur during charcoalification: implications for identifying charcoal in the fossil record

All of our current understanding of fossil charcoal structure comes from observations of modern wood charcoal produced in furnaces. These charcoals consistently show cell wall homogenization after prolonged heating (>325°C) and this is therefore considered to be a key identifying feature of fossil charcoal. Yet furnaces are unable to replicate the full combustion processes that occur during a wildfire. Here, for the first time, we have studied the microscopic structural evolution of charcoal produced using calorimetry, wherein the wood is ignited under controlled conditions and the heat release rate and other parameters measured, and the resulting charcoal studied using reflected light microscopy. We show that homogenization of cell walls is actually only a short‐lived phase of charcoal formation that occurs during the early heating stages as the pyrolysis front traverses through the wood. Cell wall homogenization is then rapidly overprinted by the thinning, distortion and breakdown of cell walls, and a notable visual increase in reflectance. Our preliminary study therefore suggests that we need to first improve our understanding of charcoal formation in order to better understand the fossil record of wildfires.     

Commerical reference shape standards use in the study of particle shape effect on laser diffraction particle size analysis

The purpose of this paper is to describe the use of LGC Promochem AEA 1001 to AEA 1003 monosized fiberanalog shape standards in the study of the effect of particle shape on laser diffraction (LD) particle size analysis (psa). The psa of the AEA standards was conducted using LD psa systems from Beckman Coulter, Horiba, and Malvern Instruments. Flow speed settings, sample refractive index values, and sample cell types were varied to examine the extent to which the shape effect on LD psa results is modified by these variables. The volume and number probability plots resulting from these measurements were each characterized by a spread in the particle size distribution that roughly extended from the breadth to the longest dimension of the particles. For most of the selected sample refractive index values, the volume probability plots were characterized by apparent bimodal distributions. The results, therefore, provide experimental verification of the conclusions from theoretical studies of LD psa system response to monosized elliptical particles in which this apparent bimodality was the predicted result in the case of flow-oriented particles. The data support the findings from previous studies conducted over the past 10 years that have called into question the verity of the tenets of, and therefore the value of the application of, the equivalent spherical volume diameter theory and the random particle orientation model to the interpretation of LD psa results from measurements made on nonspherical particles.     

Commercial reference shape standards use in the study of particle shape effect on laser diffraction particle size analysis

The purpose of this paper is to describe the use of LGC Promochem AEA 1001 to AEA 1003 monosized fiber-analog shape standards in the study of the effect of particle shape on laser diffraction (LD) particle size analysis (psa). The psa of the AEA standards was conducted using LD psa systems from Beckman Coulter, Horiba, and Malvern Instruments. Flow speed settings, sample refractive index values, and sample cell types were varied to examine the extent to which the shape effect on LD psa results is modified by these variables. The volume and number probability plots resulting from these measurements were each characterized by a spread in the particle size distribution that roughly extended from the breadth to the longest dimension of the particles. For most of the selected sample refractive index values, the volume probability plots were characterized by apparent bimodal distributions. The results, therefore, provide experimental verification of the conclusions from theoretical studies of LD psa system response to monosized elliptical particles in which this apparent bimodality was the predicted result in the case of flow-oriented particles. The data support the findings from previous studies conducted over the past 10 years that have called into question the verity of the tenets of, and therefore the value of the application of, the equivalent spherical volume diameter theory and the random particle orientation model to the interpretation of LD psa results from measurements made on nonspherical particles.     

火烧迹地木炭对兴安落叶松种子萌发的影响

通过对大兴安岭兴安落叶松火烧迹地木炭的野外调查和取样,分别选取不同来源（兴安落叶松,白桦,灌木,草本）的木炭,以及不同火烧时间（当年,1年,4年,5年）的木炭,研究不同种类木炭浸提液,以及相同种类不同火烧时间木炭浸提液对兴安落叶松种子萌发的影响。研究结果发现,不同来源、不同时间的木炭对兴安落叶松种子的萌发均有显著性的影响,但作用力的方向和大小也各不相同,这说明木炭对种子萌发的影响因素非常复杂。     

Late holocene human impact on two coastal environments in New South Wales,Australia: a comparison of Aboriginal and European impacts

There are few historical analyses quantifying impacts of human activity in Australia. This paper compares vegetation change, fire regime, erosion and eutrophication rates between the European period and the recent prehistoric past in two lake systems on the south coast of New South Wales. The variance in pollen abundance and hence species population changes increased markedly in the historical period, especially amongst understorey taxa, and this could be related to changes in the local fire regimes and to the effects of grazing. Local fire activity decreased from the prehistorical period at both sites. Erosion rates increased in the historical period and both organic and inorganic components were deposited in the lakes. Erosion episodes could be related to fire during some periods but are clearly controlled by forest disturbance and land-use at other periods. The trophic status of the lakes was increasing from before European settlement but accelerated in the recent past. This was in part due to the increased erosion rates and in part due to fertiliser application. The results suggest that lower rates of erosional and eutrophic change occur in catchments with basaltic than with Holocene sand substrata.     

Reducing chloramines in drinking water

Monochloramine is produced when drinking water containing ammonium is chlorinated. It has long been known that activated charcoal destroys monochloramine. However, exact data for the dimensioning of a dechloramination plant were lacking. Four different commercially available activated charcoals were characterized (size of particle, iodine number) and examined for their effectiveness in removing monochloramines. The degradation of monochloramine by active charcoal is based on a chemical reaction of first order between carbon and monochloramine. The types of activated charcoal considerably differ in terms of reaction velocity, due in part to the mean granular size. The final concentration of the monochloramines is influenced only by their length of stay in the activated carbon filter, the temperature and the inflow concentration. A mathematical model describes the dependence of the degradation rate of the monochloramines on various factors. With its aid a nomogram can be established with which, simply and quickly, the activated charcoal needed in a concrete case can be determined.     

Influence of Particle Size and Concentration on Rheological Behaviour of Reconstituted Apple Purees

This work investigates the impact of structural parameters on the rheological behaviour of apple purees. Reconstructed apple purees from 0 g/100 g up to 2.32 g/100 g of insoluble solids content and varying in particle size were prepared. Three different particle size distributions were obtained by mechanical treatment only, to modify both size and morphology of the particles without modifying the intrinsic rigidity of the cell walls. Rheological measurements showed that the insoluble solids content have a first order effect on the rheological behaviour of the suspensions: three concentrations domains were observed in both dynamic and flow measurements. A model is proposed for each domain. The existence of a weak network between particles is clearly shown over a critical concentration of insoluble solids (cell walls) depending on particle size distribution (semi-diluted domain). In a concentrated domain, particles are on close packing conditions and their apparent volume begin to shrink. Particle size and shape also play an important role on the rheological behaviour of reconstructed apple puree. Due to their irregular shape, cell clusters clog the medium at lower concentration compared to individual cells.     

运城盆地洪积扇全新世时期的野火与环境变化的初步探讨

通过对运城盆地典型黄土-古土壤剖面磁化率和炭屑含量的分析,研究了洪积扇全新世野火活动的规律及其与环境变化的关系。研究结果表明,在全新世早期(11500~8500 a B.P.), 气候向温湿过渡,但仍较干旱,炭屑含量较高,野火活动比较频繁,说明气候干旱是野火发生的重要原因。而全新世中期(8500~3100 a B.P.),除夏商文化时期外,炭屑含量在整个全新世时期居于最低,野火活动最为微弱,与此时期气候温暖湿润密切相关。但在夏商文化时期(3800~3500 a B.P.)炭屑浓度出现峰值,野火活动较为频繁,是人类生产和生活活动作用的结果。全新世晚期(3100~0 a B.P.)炭屑含量大幅度增加,野火活动最为频繁,一方面与气候向干旱化发展有关,另一方面与大范围的人类活动密切相关;在干旱的气候背景条件下, 人类活动加速了野火的发生频率和活动强度。     

A palaeobiological examination of the geological evidence for recurring outbreaks of the crown-of-thorns starfish,Acanthaster planci (L.)

Geological investigations of the crown-of-thorns starfish (COTS) have concluded that outbreaks are not only recent but also have occurred in the past. The evidence lies in the abundance of COTS skeletal elements found both on the sea floor and within the underlying sedimentary record. These studies are flawed in three respects. First, the processes of fossil preservation from the living population to the fossil assemblage have been ignored. Second, it has not been demonstrated that the fossil skeletal elements representing alleged outbreak populations of starfish are of the same age. Third, the existence of a relationship between the number of COTS skeletal elements sampled from the sedimentary record and the relative abundance of COTS in the once living population has not been substantiated. The limitations introduced when studying the fossil record need to be established through taphonomic analyses of the COTS. Techniques which will allow greater temporal resolution of skeletal element age include amino-acid geochronology, analysis of sedimentation mode and rate, and correlation among sub-surface cores. In order to establish a relationship between the number of fossil COTS elements and the original population size, methods must be developed which will relate the number of fossil skeletal elements to the relative abundance of starfish in both the fossil and death assemblages and then to relate the latter to the relative size of the original population. When these approaches are used together it may be possible to make some estimate of relative COTS abundances based on data contained in the fossil record.     

Evidence of recurrent wildfire from the Permian coal deposits of India: Petrographic,scanning electron microscopic and palynological analyses of fossil charcoal

In India hitherto fossil charcoal has been reported from Kashmir, Damodar Basin, and Mahanadi Basin. This work documents recurrent Cisuralian wildfire based on the occurrence of fossil charcoal from India. The authors used petrographical, palynological and SEM studies to analyze the anatomy of charred wood fragments and temperature of their formation. The fossil charcoal has been retrieved from the Cisuralian coal bearing subsurface sediments of Lower Barakar Formation (Artinskian) from Auranga Coalfield of Damodar Basin. Evidences of recurrent wildfire have been observed by the occurrence of charcoal at four levels of clastic sediments in Borehole 2N. The charcoal was subjected to petrographical, palynological and SEM studies to understand the burning temperature, fuel source and plant anatomy respectively. Petrographic studies indicate high frequency of semifusinite vis-à-vis fusinite having reflectance values ranging from 2.87% to 4.1%. The majority of the fusinite reflectance values fall in the range of 2.9%–3.5% indicating the temperature of formation of these charcoals to be at approximately 500°C. High temperature is also indicated by homogenization of cell walls under SEM. They also reveal fungal infestation and degradation in all charcoal samples. Moderate to high degree of preservation of charcoal indicates lesser transportation/post-depositional degradation suggesting a hypo-autochthonous nature. The botanical affinity of recovered spores and pollen suggest that the hinterland was dominated by gymnosperms and sub-dominated by filicopsids, sphenopsids, and lycopsids which contributed to the fuel source.     

Changes of the forest-savanna boundary in Brazilian Amazonia during the Holocene revealed by stable isotope ratios of soil organic carbon

The possibility of ecosystem boundary changes in northern Brazilian Amazonia during the Holocene period was investigated using soil organic carbon isotope ratios. Determination of past and present fluctuations of the forest-savanna boundary involved the measurement of natural ¹³C isotope abundance, expressed as ¹³C, in soil organic matter (SOM). SOM ¹³C analyses and radiocarbon dating of charcoal fragments were carried out on samples derived from soil profiles taken along transects perpendicular to the ecotonal boundary. SOM ¹³C values in the upper soil horizons appeared to be in equilibrium with the overlying vegetation types and did not point to a movement of the boundary during the last decades. However, ¹³C values obtained from deeper savanna and forest soil layers indicated that the vegetation type has changed in the past. In current savanna soil profiles, we observed the presence of mid-Holocene charcoals derived from forest species: fire frequency at that time was probably greater, and more extensive savanna may have resulted. Isotope data and the presence of these charcoals thus suggest that the forest-savanna boundary has shifted significantly in the recent Holocene period, forest being more extensive during the early Holocene than today. During the middle Holocene, the forest could have strongly regressed, and fires appeared, with a maximum development of the savanna vegetation. At the beginning of the late Holocene, the forest may have invaded a part of this savanna, and fires occurred again.     

A Monte Carlo simulation of the determination of mean particle volume using the Cavalieri estimator

BACKGROUND: A common morphometric problem is the determination of an estimate of the size of biological particles obtained from measurements made on a sample of profiles observed in sections. Results are reported typically in terms of mean caliper diameter or mean volume of the particle. METHODS: We have investigated the use of the Cavalieri estimator for obtaining estimates of mean particle volume using a Monte Carlo simulation. Samples of spherical and ellipsoidal particles were generated by computer and serially sectioned at a fixed mean thickness with a small, imposed random variation. The area of each profile was determined and the volume of the particle was calculated according to the Cavalieri estimator. The influence on the estimate of the mean particle volume and its 95% confidence interval was evaluated for several variables: the shape of the particles, the standard deviation of the particle volume in the population, the section thickness, and the standard deviation of the section thickness. RESULTS: The results obtained with the Cavalieri estimator correspond favorably with those obtained with previously reported alternative methods. This leads to a recommendation for the strong consideration for the use of the Cavalieri estimator in cases in which it is technically feasible to obtain at least three sections through the individual particles. Graphs are provided, which relate the confidence interval for the mean volume to the number of particles measured.     

Impact of hydrology on free-living and particle-associated microorganisms in a river floodplain system (Danube, Austria)

1. A floodplain segment of the Danube River downstream of Vienna was studied during the hydrologically most dynamic phase (spring–summer) to evaluate the significance of connection between the main channel and the floodplain segment for particle abundance and quality as well as for bacterial and viral parameters, both free‐living and attached to particles. 2. Hydrological connectivity between the main channel and its floodplain segment (expressed as water age) influenced particle abundance and quality. Polysaccharide‐containing particles [Alcian positive‐stained particles (ASP)] and protein‐containing particles [Coomassie positive‐stained particles (CSP)] each contributed a substantial fraction to total suspended solids and were both positively related to water age. ASP were about twice as abundant as CSP. 3. Water age influenced bacterial and viral abundance and the bacterioplankton productivity in the surrounding water. Free‐living bacterial abundance and their bacterial secondary production (BSP) increased continuously with water age, best described by a linear regression. Water age also significantly impacted BSP and per cell BSP of bacteria attached to particles. The abundance of attached bacteria and viruses was not influenced by water age. 4. Bacteria and viruses on particles were influenced by particle quality. Their abundance on particles was closely related to particle size. Particle‐attached bacteria accounted on average for 30.34% (± 3.09) of the total bacterial abundance. A variable and occasionally significant proportion of viruses, between 0.43% and 35.06%, were associated with particulate material. 5. Bacteria attached to particles were significantly more productive than their free‐living counterparts. Their per‐cell activity was on average 8.6 times higher than that of the free‐living fraction. 6. Hydrological connectivity between the Danube River and its floodplain is crucial not only for the exchange of water, sediment and nutrients, but also for microbiota, thus influencing microbial life, distribution and activity.     

Post‐fire vegetation and climate dynamics in low‐elevation forests over the last three millennia in Yellowstone National Park

Conifer forests of the western US are historically well adapted to wildfires, but current warming is creating novel disturbance regimes that may fundamentally change future forest dynamics. Stand‐replacing fires can catalyze forest reorganization by providing periodic opportunities for establishment of new tree cohorts that set the stage for stand development for centuries to come. Extensive research on modern and past fires in the Northern Rockies reveals how variations in climate and fire have led to large changes in forest distribution and composition. Unclear, however, is the importance of individual fire episodes in catalyzing change. We used high‐resolution paleoecologic and paleoclimatic data from Crevice Lake (Yellowstone National Park, Wyoming, USA), to explore the role of fire in driving low‐elevation forest dynamics over the last 2820 yr. We addressed two questions: 1) did low‐elevation forests at Crevice Lake experience abrupt community‐level vegetation changes in response to past fire events? 2) Did the interaction of short‐term disturbance events (fire) and long‐term climate change catalyze past shifts in forest composition? Over the last 2820 yr, we found no evidence for abrupt community‐level vegetation transitions at Crevice Lake, and no evidence that an interaction of climate and fire produced changes in the relative abundance of dominant plant taxa. In part, this result reflects limitations of the datasets to detect past event‐specific responses and their causes. Nonetheless, the relative stability of the vegetation to fires over the last 2820 yr provides a local baseline for assessing current and future ecological change. Observations of climate–fire–vegetation dynamics in recent decades suggest that this multi‐millennial‐scale baseline may soon be exceeded.     

Contrasting long‐term records of biomass burning in wet and dry savannas of equatorial East Africa

Rainfall controls fire in tropical savanna ecosystems through impacting both the amount and flammability of plant biomass, and consequently, predicted changes in tropical precipitation over the next century are likely to have contrasting effects on the fire regimes of wet and dry savannas. We reconstructed the long‐term dynamics of biomass burning in equatorial East Africa, using fossil charcoal particles from two well‐dated lake‐sediment records in western Uganda and central Kenya. We compared these high‐resolution (5 years/sample) time series of biomass burning, spanning the last 3800 and 1200 years, with independent data on past hydroclimatic variability and vegetation dynamics. In western Uganda, a rapid (<100 years) and permanent increase in burning occurred around 2170 years ago, when climatic drying replaced semideciduous forest by wooded grassland. At the century time scale, biomass burning was inversely related to moisture balance for much of the next two millennia until ca. 1750 ad , when burning increased strongly despite regional climate becoming wetter. A sustained decrease in burning since the mid20th century reflects the intensified modern‐day landscape conversion into cropland and plantations. In contrast, in semiarid central Kenya, biomass burning peaked at intermediate moisture‐balance levels, whereas it was lower both during the wettest and driest multidecadal periods of the last 1200 years. Here, burning steadily increased since the mid20th century, presumably due to more frequent deliberate ignitions for bush clearing and cattle ranching. Both the observed historical trends and regional contrasts in biomass burning are consistent with spatial variability in fire regimes across the African savanna biome today. They demonstrate the strong dependence of East African fire regimes on both climatic moisture balance and vegetation, and the extent to which this dependence is now being overridden by anthropogenic activity.     

黔西高原MIS3-MIS2期炭屑记录与火灾模式研究

火灾与气候、植被存在复杂的关系,搞清东亚季风区的火灾模式及其发生机制,对预测未来气候变化及火灾防治具有重要意义。通过对黔西高原MIS3—MIS2期间的古湖相沉积物进行炭屑分析并结合AMS~(14)C测年数据研究发现:MIS3晚期以来研究区的火灾主要发生于36.3—35 cal ka BP、26.2—17.6 cal ka BP期间,中粒炭屑和大炭屑分别在35、26.2、23.6 cal ka BP记录到3次地方火。研究区炭屑记录对冷干事件响应敏感,炭屑峰值区对应Heinrich事件(H事件)、末次冰盛期(LGM)等干旱事件,低值区对应DO事件,呈现千年旋回的特征。比对东亚地区的炭屑记录发现,在大范围的东亚季风区MIS2期比MIS3末期在火的强度和频率上都要高,与欧洲模式显著不同。火的发生机制可能受气候因素的控制,同时受植被类型的影响。     

Vegetation dynamics and anthropogenically forced changes in the Estanilles peat bog (southern Pyrenees) during the last seven millennia

Estanilles peat bog, located in the northeastern Iberian peninsula, was studied to determine the anthropogenic changes in the landscape over the past seven millennia. The pollen diagram and sedimentary charcoal analyses from this site permit us to reconstruct the landscape changes in an area of both Mediterranean and Atlantic influence. In addition, Montarenyo ombrotrophic peat bog was studied to strengthen the analysis of data from more recent centuries. This paper attempts a reconstruction of historical cultural landscapes using two complementary palaeobotanical proxies (pollen and charcoal) in high mountain environments. The macroscopic charcoal record shows a fire signal since 7500?cal. b.p. However, the relationship between fire frequency and human impact is not always linear. This divergence is linked to fuel availability and fire activity. Fire has been used repeatedly to clear ground and to maintain open areas, and has been a key tool for the management of these high mountain areas. The intensity of use of the landscape implies the expansion of agricultural areas into higher altitudes, including cereal cultivation above 2,200?m a.s.l., during the Middle Ages. The first clear human influence detected in the pollen percentage data is recorded between 6000 and 7000?cal. b.p. and, until present times, the greatest changes in vegetation and landscape history occurred during periods of particular specialization in socioeconomic activities during the Middle Ages.