Prehistoric Fires Research Articles

Examining the effects of climate change and human impacts on a high-resolution, late Holocene paleofire record from South Africa's winter rainfall zone

Fire is central to the Cape Floristic Region's highly biodiverse and disturbance-adapted Fynbos Biome. However, prehistoric fire regimes, their ecological consequences, and their relationships with large-scale climate drivers and human activities remain poorly understood. Here, we use a high-resolution sedimentary charcoal record from Verlorenvlei, a coastal lake situated on the west coast, to interrogate links between fire, climate, and pastoralism in the Fynbos Biome. Our record has a robust chronology supported by 24 radiocarbon dates and provides a continuous sedimentary sequence spanning the last 4200 years, documenting fire activity before and after the local arrival of pastoralists in the Verlorenvlei area ∼1500 cal years BP. Fire at Verlorenvlei over the last 4200 years is variable, with relatively low activity until ∼2000 cal years BP, after which variable but generally higher fire activity occurs until the highest period of fire activity from ∼1450 to 1800 CE (∼500–150 cal years BP). The increase in fire activity ∼2000 years ago corresponds with a shift in the diatom assemblage at Verlorenvlei from marine towards brackish and freshwater species, reflecting increased precipitation derived from a strengthening of the southern westerly winds. The peak in fire activity beginning ∼1450 CE (∼500 cal years BP), near the onset of the Little Ice Age, tracks a second diatom-inferred strengthening of the westerly winds. Other southern hemisphere and Antarctic records further corroborate this increased westerly influence after ∼2000 years. Linear regression modeling on the fire record indicates that moisture availability is the primary driver of fire at Verlorenvlei, with little evidence that human populations influenced fire. Our reconstruction suggests that fire activity at Verlorenvlei is limited by moisture availability and that wetter conditions facilitate increased vegetation (i.e., fuel) and intensified fire at this otherwise fuel-limited site. This work has implications for management and conservation decisions in response to future predictions of a warmer and drier climate along South Africa's west coast.

The applicability of Raman spectroscopy in the assessment of palaeowildfire intensity

Evidence of wildfires in deep time is preserved as fossilised charcoal fragments in the rock record and inertinite macerals in coal. Historically, charcoal reflectance has been utilised to assess the formation temperature of these charcoals, and thus burning intensities of prehistoric fires. This is achieved by quantifying reflectance variability as a function of changes in charcoal microstructure with temperature. Raman spectroscopy been shown to similarly assess microstructure in carbonaceous organic matter with thermal maturation. However, there have been few applications of Raman spectroscopy to wildfire-derived charcoals, modern or prehistoric. Little consideration has also been paid to the nature and applicability of derived parameters in assessing intensity. This study presents a novel assessment of Raman spectroscopy as a method for interpreting palaeowildfire burning intensity. Spectra were obtained from experimentally pyrolysed Calluna vulgaris material, generated across a range of natural wildfire temperatures, and subsequent derived parameters were compared with established principles. For assessing changes in palaeowildfire intensity, this study has found the best correlations between thermal maturity and; D-band full-width at half-maximum (D-FWHM) and the D−/G-band full-width at half-maximum ratio (D-FWHM/G-FWHM). Additional parameters, commonly applied to Raman studies of charcoal, are otherwise influenced by non-linearity. The influence of precursor material on charcoal microstructure has also been derived, indicating further complexity when assessing heterogenous samples. Our results indicate that, whilst Raman spectroscopy offers extraordinary potential for understanding prehistoric and modern wildfire intensity, parameters and further analyses used require measured consideration.

Magnetic fabric and archaeomagnetic analyses of anthropogenic ash horizons in a cave sediment succession (Crvena Stijena site, Montenegro)

SUMMARY An archaeomagnetic, rock magnetic and magnetic fabric study has been carried out on seven anthropogenic ash horizons in the Middle Palaeolithic sedimentary level XXIV at the rock shelter of Crvena Stijena (‘Red Rock’), Montenegro. The study has multiple goals, including the identification of iron bearing minerals formed during combustion, assessment of the suitability of these combustion features for recording the Earth´s magnetic field direction, revelation of the magnetic fabric and its significance in the characterization of cave (rock shelter) burnt facies, and identification of post-burning alteration processes. Magnetite has been identified as the main ferromagnetic component of the ash. The ash layers exhibit a high thermomagnetic reversibility in contrast to the irreversible behaviour of their subjacent burnt black layers which is related to the different temperatures attained. Seven mean archaeomagnetic directions were obtained with acceptable statistical values indicating that these features recorded the field direction at the time of burning. However, some of them are out of the expected range of secular variation for mid-latitude regions suggesting post-burning alterations. The magnetic fabric of the ash was characterized by anisotropy of low field magnetic susceptibility measurements. Statistical analysis (box and whisker plot) of the basic anisotropy parameters, such as foliation, lineation, degree of anisotropy and the shape parameter, along with the alignment of the principal susceptibilities on stereoplots, revealed variation among the ash units. The diverse, oblate to prolate, lineated or strongly foliated, quasi-horizontally and vertically oriented fabrics of the units may indicate different slope processes, such as orientation by gravity, solifluction, run-off water, quasi-vertical migration of groundwater and post-burning/post-depositional alteration of the fabric by rockfall impact. In sum, the magnetic characterization of the ash layers has shown the occurrence of different post-burning alteration processes previously not identified at the site. Alteration processes in prehistoric combustion features are often identified from macroscopic observations but our study demonstrates that multiple processes can affect them and are usually unnoted because they take place on a microscopic scale. Their identification is critical for a correct chronological and cultural interpretation of a site (e.g. collection of samples for dating, stratigraphic displacement of remains), especially if significant alterations are involved. Magnetic methods are therefore a powerful but underutilized tool in palaeolithic research for the identification and evaluation of taphonomic processes affecting prehistoric fires.

Using phytolith analysis to reconstruct prehistoric fire regimes in central coastal California

Over the last century, northern coastal scrub has encroached into open grasslands along the central California coast, increasing fire risk in coastal wildland–urban interfaces. Understanding prehistoric ecological conditions is crucial for fire mitigation projects. Current estimates of these conditions in coastal California grasslands and shrublands are largely speculative because tree ring data, lake sediment evidence and ethnographic information are sparse. Phytolith analysis is an alternative palaeoecological tool that has been successfully used to reconstruct the extent of prehistoric grass cover in California. Our study uses phytolith analysis of soil samples from the East Bay hills of the San Francisco Bay region as a novel approach to estimate prehistoric grassland distribution and infer fire frequency in central coastal California. Our data strongly indicate that many areas in the region were dominated by perennial bunchgrasses for at least several hundred years before European contact. Because grass-dominated grasslands in the East Bay hills are disturbance-dependent, our data suggest prehistoric fire frequency was of the order of 5 years or less in the region. Phytolith analysis is a useful technique for prehistoric fire regime reconstruction for grasslands and shrublands worldwide, leading to improved, data-based land management.

The organic signature of an experimental meat-cooking fireplace: The identification of nitrogen compounds and their archaeological potential

A better understanding of the operation and use of prehistoric fires is fundamental to interpreting the organization of living spaces. Following a previous study that focused on the organic signatures of fireplaces fueled with wood and/or bones, this study targeted the completion of an experimental reference database through the addition of a wood-fueled fireplace dedicated to the cooking of meat. Different sedimentary features of this experimental fireplace were visually identified (e.g. darkening, reddening), sampled, and subjected to geochemical analysis. Corg and N contents were quantified, samples were extracted with organic solvents and analyzed through GC–MS and bulk organic matter was characterized through py(TMAH)-GC–MS. Five different samples were studied and compared with a control sample, representative of the local background. A significant increase of Corg and N contents was measured for the three samples presenting darkened or charred caracteristics. The meat-cooking fireplace seems to be characterized by the strong contribution of nitrogen, which was visible in elementary analyses as well as in the molecular composition of solvent extracts, and bulk organic matter. More specifically, compounds containing nitrile functions, amides, N-heterocyclic and N-aromatic compounds could be detected in solvent extracts. Amines, amides, N-heterocyclic and N-aromatic compounds could be identified in py(TMAH)-GC–MS. Some of these compounds present a relative stability in soils and could therefore aid in our comprehension and functional interpretations of archaeological fireplaces, and may, more particularly, make it possible to highlight the use of fireplaces for the cooking of meat.

Identifying natural and anthropogenic drivers of prehistoric fire regimes through simulated charcoal records

Archaeological and paleoecological studies demonstrate that human-caused fires have long-term influences on terrestrial and atmospheric systems, including the transformation of “wild” landscapes into managed, agricultural landscapes. Sedimentary charcoal accumulations alone provide only limited information about the influence of human-caused fires on long-term fire regimes. Computational modeling offers a new approach to anthropogenic fire that links social and biophysical processes in a “virtual laboratory” where long-term scenarios can be simulated and compared with empirical charcoal data. This paper presents CharRec, a computational model of landscape fire, charcoal dispersion, and deposition that simulates charcoal records formed by multiple natural and anthropogenic fire regimes. CharRec is applied to a case study in the Canal de Navarrés region in eastern Spain to reveal the role of human-driven fire regimes during the early and middle Holocene. A statistical comparison of simulated charcoal records and empirical charcoal data from the Canal de Navarrés indicates that anthropogenic burning, following the Neolithic transition to agro-pastoral subsistence, was a primary driver of fire activity during the middle Holocene.

Fire in the Early Palaeolithic: Evidence from burnt small mammal bones at Cueva Negra del Estrecho del Río Quípar, Murcia, Spain

The development of pyrotechnology is a hallmark of human history, providing our ancestors with warmth, security and cooked food. Evidence for fire use before 400 thousand years ago (kya) remains contentious due largely to the taphonomically fragile nature of charcoal and ash. As such, it is imperative to the study of prehistoric fire that we develop techniques and methodologies for identifying anthropogenic fire use via more robust materials. A new methodology described by Fernández-Jalvo and Avery (2015) based on small mammal taphonomy to identify high intensity fire events from the distant past is replicated herein. When we applied this method to assemblages from Cueva Negra del Estrecho del Río Quípar, an upland rock-shelter in southeastern Spain, dated to between 780kya and 980kya, we recognized a spatial relationship between highly heat modified micromammal specimens and a previously reported delineated feature of thermally altered and carbonate rich sediment which also includes heat-fractured chert and calcined bone (the fire feature). The proportion of heavily heat-modified specimens (charred and/or calcined specimens) identified within the stratigraphic context associated with the fire feature proved statistically significant (x2=169.18, p<0.001) when compared with the proportion of similarly modified specimens from overlying deposits (within other stratigraphic layers). The degree of discolouration seen on the micromammal remains within the fire feature has been linked to temperatures exceeding 600°C (Shipman et al., 1984), and as such supports claims that the fire feature may have an anthropogenic origin. Environmental scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) of bone specimens confirms that this discolouration is due to burning rather than post-depositional mineral staining. This confirms that methodology, which represents a novel line of evidence for identifying pyrotechnical events at early Palaeolithic sites, can be used to identify potentially anthropogenic fire events from the distant past when alternative scenarios are excluded. Furthermore, studies of this type showcase the value of including detailed taphonomic studies of microfauna assemblages within multidisciplinary research projects.

Neolithic to Bronze Age (4850–3450 cal. BP) fire management of the Alpine Lower Engadine landscape (Switzerland) to establish pastures and cereal fields

Agro-pastoral activities in the past act as environmental legacy and have shaped the current cultural landscape in the European Alps. This study reports about prehistoric fire incidents and their impact on the flora and vegetation near the village of Ardez in the Lower Engadine Valley (Switzerland) since the Late Neolithic Period. Pollen, charcoal particles and non-pollen palynomorphs preserved in the Saglias and Cutüra peat bog stratigraphies were quantified and the results compared with the regional archaeological evidence. Anthropogenic deforestation using fire started around 4850 cal. BP at Saglias and aimed at establishing first cultivated crop fields (e.g. cereals) and small pastoral areas as implied by the positive correlation coefficients between charcoal particles and cultural and pastoral pollen indicators, as well as spores of coprophilous fungi. Pressure on the natural environment by humans and livestock continued until 3650 cal. BP and was followed by reforestation processes until 3400 cal. BP because of climatic deterioration. Thereafter, a new, continuous cultivation/pastoral phase was recorded for the Middle to Late Bronze Age (3400–2800 cal. BP). After rather minor human impact during the Iron Age and Roman Period, intensive agriculture was recorded for the Medieval Period. The area around Ardez was used for crop cultivation from about 1000 cal. BP until the start of the ‘Little Ice Age’ (600 cal. BP). Despite a land-use reorganisation, the following gradual decrease in agricultural activities led to the extant mixture of a cultivated, grazed and forested landscape in the Lower Engadine. In addition, this study demonstrates the excellent value of the fungus Gelasinospora as a highly local marker of past and today’s fire incidents, as well as of the use of micro-charcoals from pollen slides and macro-charcoals (&gt;150 µm) from pollen sample residues for the reconstruction of short- and long-term fire histories.

Primary Succession on a Hawaiian Dryland Chronosequence.

We used measurements from airborne imaging spectroscopy and LiDAR to quantify the biophysical structure and composition of vegetation on a dryland substrate age gradient in Hawaii. Both vertical stature and species composition changed during primary succession, and reveal a progressive increase in vertical stature on younger substrates followed by a collapse on Pleistocene-aged flows. Tall-stature Metrosideros polymorpha woodlands dominated on the youngest substrates (hundreds of years), and were replaced by the tall-stature endemic tree species Myoporum sandwicense and Sophora chrysophylla on intermediate-aged flows (thousands of years). The oldest substrates (tens of thousands of years) were dominated by the short-stature native shrub Dodonaea viscosa and endemic grass Eragrostis atropioides. We excavated 18 macroscopic charcoal fragments from Pleistocene-aged substrates. Mean radiocarbon age was 2,002 years and ranged from < 200 to 7,730. Genus identities from four fragments indicate that Osteomeles spp. or M. polymorpha once occupied the Pleistocene-aged substrates, but neither of these species is found there today. These findings indicate the existence of fires before humans are known to have occupied the Hawaiian archipelago, and demonstrate that a collapse in vertical stature is prevalent on the oldest substrates. This work contributes to our understanding of prehistoric fires in shaping the trajectory of primary succession in Hawaiian drylands.

Amazonia and the Anthropocene: What was the spatial extent and intensity of human landscape modification in the Amazon Basin at the end of prehistory?

The nature and spatial scale of prehistoric human landscape modifications in Amazonia are enduring questions. Original conceptions of the issues by archaeologists published more than 40 years ago posited little human influence because of putative environmental constraints. Empirical data accumulated more recently demonstrated dense, permanent settlements along major watercourses of the central and southern Amazon, and profound landscape alterations in seasonally flooded savanna regions of Bolivia. These results led some investigators to propose that most to all of Amazonia was heavily populated and modified before European arrival, and that prehistoric fires and forest clearing were of such a massive scale that post-Columbian reforestation was a significant contributor to decreasing atmospheric CO2 levels and the onset of the ‘Little Ice Age’. Recent data generated from investigations of soils sampled from underneath standing terra firme forests in parts of the western Amazon indicate ephemeral ancient human occupation and little vegetation disturbance there. These issues are central to ongoing discussions surrounding the classification and timing of the Anthropocene, because a geological epoch proposed on the basis of profound human alteration of environments and considerations of when during the Holocene it should begin, require robust paleo-environmental and archaeological data from major, critically important zones such as the Amazon Basin. This paper reviews debates and existing information on prehistoric human influences in Amazonia, provides new data from the western Amazon, and attempts to arrive at reasonable conclusions based on the available empirical data.

Prehistoric fires and the shaping of colonial transported landscapes in southern California: A paleoenvironmental study at Dune Pond, Santa Barbara County

Using a novel combination of paleoecologic proxies including pollen, non-pollen palynomorphs (NPPs), macroscopic charcoal, and Spheroidal Carbonaceous Particles (SCPs), 5000 years of landscape change, fire history and land-use have been reconstructed from Dune Pond, Santa Barbara County, California. The pond was sensitive to Holocene regional climatic variability, showing different phases of lower (4600–3700 cal yr BP, 2100–700 cal yr BP, historical period) and higher (3700–2100 cal yr BP, 700–150 cal yr BP) local moisture availability. During this period the landscape was dominated by a coastal mosaic vegetation including dune mats, coastal scrub and salt marshes on the dunes and backdunes, with chaparral and oak woodland growing in the valley plains and foothills. Fire was intimately linked with such dominating mosaic vegetation, and the combination of wet conditions and the presence of nearby human settlement were a trigger favoring coastal fires for at least two periods: from 3100 to 1500 cal yr BP and from 650 cal yr BP until the 18th century. In both cases fire was an important tool to keep an open coastal landscape attractive to hunting wildlife. Finally, matching this varied range of high-resolution paleoecological proxies with historical records we could characterize the development of colonial transported landscapes following the Euro-American settlement of Santa Barbara. The introduction of livestock grazing by Spanish colonists favored erosive processes and the introduction of fecal-borne parasites in freshwater bodies, negatively impacted salt and brackish coastal marshes, and promoted the invasion of alien grasses and ruderals. This agro-pastoral landscape was consolidated during the American period, with a greater role for cultivation, the development of industrial activities and increased population. Despite negative environmental consequences such as the loss of native habitats, exotic land-uses and plants introduced during the historical period significantly contributed to the configuration of a cultural landscape which forms part of the cultural heritage of California.

Past and Present Vulnerability of Closed-Canopy Temperate Forests to Altered Fire Regimes: A Comparison of the Pacific Northwest, New Zealand, and Patagonia

The relative importance of people and climate in shaping prehistoric fire regimes is debated around the world, and this discussion has helped inform our understanding of past and present ecosystem dynamics. Evidence for extensive anthropogenic burning of temperate closed-canopy forests prior to European settlement is geographically variable, and the factors responsible for this variability are not well resolved. We set out to explain the differences in the influence of prehistoric human-set fires in seasonally dry forest types in the Pacific Northwest, New Zealand, and northern Patagonia by comparing the fire traits of dominant taxa, postfire vegetation recovery, long-term climate trends, and human activities that may have motivated burning. Our analysis suggests that ecological and climatic factors explain much of the differences in how these mesic–dry forests responded to prehistoric anthropogenic burning. Understanding past human–environment interactions at regional scales is an important step for assessing the impact of biomass burning at all scales.

Experimental Micromorphology on Burnt Shells of Anomalocardia brasiliana (Gmelin 1791) (Bivalvia, Veneridae) and Its Potential for Identification of Combustion Features on Shell‐Matrix Sites

The identification of in situ or reworked hearths in archaeological sediments is currently one of the main topics in archaeological micromorphology. In the case of shell‐matrix sites (shell mounds and middens), the clast‐supported matrix and high porosity can hamper the clear identification of combustion features. Previous experimental approaches were useful to identify in thin section the transformations induced by heating in mollusk shells, which are related to its mineralogy. Since different species of mollusks contain diverse mineralogy (aragonite, calcite, or both), it is expected that each species follows a specific thermal behavior, although similar general trends exist. In this short contribution, a set of valves of the mollusk Anomalocardia brasiliana (Gmelin 1791) (Bivalvia, Veneridae), the most important component of Brazilian shell mounds, was heated in a muffle furnace at temperatures from 200°C to 800°C. Thin sections were made and their description is presented for the identification of burnt shell of A. brasiliana. This information can help to infer the temperature of prehistoric fires and can assist in the identification of in situ versus reworked hearths in shell‐matrix sites.

Different mechanisms of magnetisation recorded in experimental fires: Archaeomagnetic implications

We present here the archaeomagnetic and rock-magnetic results obtained from the experimental recreation of prehistoric fires on a clayish soil substratum. By using a system of thermocouples that allows the control of temperatures and heat penetration with depth, the magneto-mineralogical transformations as well as the ability to acquire magnetic remanences are studied. A detailed set of rock-magnetic analyses – carried out both on surface and depth with a millimetre scale resolution– shows the creation of post-burn magnetite over the entire surface of the hearth, thus promoting a distinguishable magnetic enhancement. On the basis of a detailed control of temperatures, interesting differences between areas (centre vs. periphery) were observed and two different mechanisms of magnetisation have been recorded. The central area which exceeded 600 °C acquired a thermal remanent magnetisation (TRM) and the periphery, which was heated up to 300 °C, recorded a thermo-chemical (TCRM) remanent magnetisation. The most noticeable mineralogical changes are focused to the first centimetre of the central area, where single-domain magnetite has been created. The implications of these results for archaeomagnetic and palaeointensity studies as well as their utility for the detection of fire in archaeological sites are discussed.

Late Holocene geomorphic record of fire in ponderosa pine and mixed-conifer forests, Kendrick Mountain, northern Arizona, USA

Long-term fire history reconstructions enhance our understanding of fire behaviour and associated geomorphic hazards in forested ecosystems. We used 14C ages on charcoal from fire-induced debris-flow deposits to date prehistoric fires on Kendrick Mountain, northern Arizona, USA. Fire-related debris-flow sedimentation dominates Holocene fan deposition in the study area. Radiocarbon ages indicate that stand-replacing fire has been an important phenomenon in late Holocene ponderosa pine (Pinus ponderosa) and ponderosa pine–mixed conifer forests on steep slopes. Fires have occurred on centennial scales during this period, although temporal hiatuses between recorded fires vary widely and appear to have decreased during the past 2000 years. Steep slopes and complex terrain may be responsible for localised crown fire behaviour through preheating by vertical fuel arrangement and accumulation of excessive fuels. Holocene wildfire-induced debris flow events occurred without a clear relationship to regional climatic shifts (decadal to millennial), suggesting that interannual moisture variability may determine fire year. Fire-debris flow sequences are recorded when (1) sufficient time has passed (centuries) to accumulate fuels; and (2) stored sediment is available to support debris flows. The frequency of reconstructed debris flows should be considered a minimum for severe events in the study area, as fuel production may outpace sediment storage.

What Constitutes a Natural Fire Regime? Insight from the Ecology and Distribution of Coniferous Forest Birds in North America

Bird species that specialize in the use of burned forest conditions can provide insight into the prehistoric fire regimes associated with the forest types that they have occupied over evolutionary time. The nature of their adaptations reflects the specific post-fire conditions that occurred prior to the unnatural influence of humans after European settlement. Specifically, the post-fire conditions, nest site locations, and social systems of two species (Bachman’s sparrow [Aimophila aestivalis] and red-cockaded woodpecker [Picoides borealis]) suggest that, prehistorically, a frequent, low-severity fire regime characterized the southeastern pine system in which they evolved. In contrast, the patterns of distribution and abundance for several other bird species (black-backed woodpecker [Picoides arcticus], buff-breasted flycatcher [Empidonax fulvifrons], Lewis’ woodpecker [Melanerpes lewis], northern hawk owl [Surnia ulula], and Kirtland’s warbler [Dendroica kirtlandii]) suggest that severe fire has been an important component of the fire regimes with which they evolved. Patterns of habitat use by the latter species indicate that severe fires are important components not only of higher-elevation and high-latitude conifer forest types, which are known to be dominated by such fires, but also of mid-elevation and even low-elevation conifer forest types that are not normally assumed to have had high-severity fire as an integral part of their natural fire regimes. Because plant and animal adaptations can serve as reliable sources of information about what constitutes a natural fire regime, it might be wise to supplement traditional historical methods with careful consideration of information related to plant and animal adaptations when attempting to restore what are thought to be natural fire regimes.

Where were the hearths: an experimental investigation of the archaeological signature of prehistoric fire technology in the alluvial gravels of the Southern Plains

The interpretation that a rock has been subjected to cultural utilization is a basic element of hunter-gatherer research. The fracture mechanics of the flaked stone tool production process are well understood and the material residues are routinely identified during fieldwork. Conversely, non-percussion processes such as hot-rock technology, which can result in rock fracture, are less well understood. An experimental study has been developed to examine the fractured gravels observed at a prehistoric site on the Southern Plains (USA). The experiment has sought to determine whether cultural or natural agencies were responsible for the production of the angularly fractured rocks. The positive results of the experiment indicate that not only were humans most likely responsible for the breakages, but also that the fractured rocks often exhibit distinctive morphologies that may be identified during fieldwork. This simple experimental methodology is applicable to other hunter-gatherer sites where the depositional environment is not conducive to the structural preservation of features such as hearths.

PHYTOLITH EVIDENCE FOR THE LACK OF A GRASS UNDERSTORY IN A SEQUOIADENDRON GIGANTEUM (TAXODIACEAE) STAND IN THE CENTRAL SIERRA NEVADA, CALIFORNIA

ABSTRACT Tree ring fire-scars in Sequoiadendron giganteum (giant sequoia) stands record a high frequency, low intensity, prehistoric fire regime. Difficulties achieving short prehistoric fire return intervals with prescribed burns at a S. giganteum stand in Calaveras Big Trees State Park, California, currently characterized by dense tree cover with little understory vegetation due to over a century of fire suppression, suggest that a prehistoric grass understory provided fine fuel required for frequent fire spread. We used phytolith analysis to test this hypothesis. Phytoliths, microscopic silica bodies found in many plants but produced in large quantities with distinctive morphotypes in grasses, are preserved for thousands of years in the soil. Soils under vegetation with extensive prehistoric grass cover retain a high concentration of grass phytoliths regardless of historic vegetation changes. Phytoliths were extracted from soil samples taken from pits dug at 14 plots throughout a S. giganteum stand in ...

Age of A2 Horizon Charcoal and Forest Structure near Porto Trombetas, Pará, Brazil1

ABSTRACTTo study the structure and composition of old‐growth forest in the Saracá‐Taquera National Forest near Porto Trombetas, Brazil, we established 36 0.25 ha plots and described the vegetation. We collected charcoal from the A2 soil horizon of each plot for radiocarbon dating. Although fires have been very rare in this forest during historic times, the presence of charcoal in these soils indicates fire at some earlier period. The ages (conventional radiocarbon age adjusted to 1997) of the charcoal ranged from 177 to 1547 years. These ages, however, did not correlate significantly with any of several measures of biodiversity or stand characteristics. The relative uniformity of the current old‐growth forest indicates that either the prehistoric fires were of such low intensity that they had little long‐term effect on the vegetation or that the present stands have progressed to near steady state.

Age of A2 Horizon Charcoal and Forest Structure near Porto Trombetas, Pará, Brazil1

To study the structure and composition of old-growth forest in the Saracá-Taquera National Forest near Porto Trombetas, Brazil, we established 36 0.25 ha plots and described the vegetation. We collected charcoal from the A2 soil horizon of each plot for radiocarbon dating. Although fires have been very rare in this forest during historic times, the presence of charcoal in these soils indicates fire at some earlier period. The ages (conventional radiocarbon age adjusted to 1997) of the charcoal ranged from 177 to 1547 years. These ages, however, did not correlate significantly with any of several measures of biodiversity or stand characteristics. The relative uniformity of the current old-growth forest indicates that either the prehistoric fires were of such low intensity that they had little long-term effect on the vegetation or that the present stands have progressed to near steady state.