Phytolith Assemblages Research Articles

The missing crop: investigating the use of grasses at Els Trocs, a Neolithic cave site in the Pyrenees (1564 m asl)

The issue of resource exploitation, both plants and animals, by Neolithic communities has always attracted vast interest. In particular, resource exploitation at mountain cave sites is still being widely discussed. This paper explores the use of grass resources at the archaeological site of Els Trocs (Aragón, Spain), a Neolithic mountain site in the Pyrenees. The analysis of phytolith samples suggests that grasses growing in the surrounding of the site were widely used. The morphological assemblages identified, and their spatial distribution, indicate that wild grasses were probably used as floor spread. The integrated approach used in this study, combining phytolith, spherulite and micromorphological analyses, confirms this hypothesis. Furthermore, the analysis of phytolith assemblages and micromorphological traits indicate the seasonal occupation of the site, placing human frequentation at this location during late spring/early summer. Several studies have highlighted the presence of charred seeds of domesticated cereals in the archaeological record of mountain cave sites however, in many instances, whether these crops were cultivated near the sites or whether the grains were transported to the cave from the valley bottom remains under debate. This paper also contributes to this debate by showing that no crop-processing activities were taking place at the site.

Análisis Fitolítico de la Formación Tezanos Pinto (Pleistoceno Tardío—Holoceno Temprano) en el Sector Sudoeste de la Provincia de Entre Ríos (Argentina)

Abstract. PHYTOLITH ANALYSIS OF TEZANOS PINTO FORMATION (LATE PLEISTOCENE-HOLOCENE) IN THE SOUTHWESTERN REGION OF ENTRE RIOS PROVINCE (ARGENTINA). Loess deposits are the main component of the Late Quaternary sequences of the Pampa plains (South America). The Last Glacial Maximum loess represents a depositional unit of the Pampean Aeolian System that evidences the expansion of semiarid conditions to the northeast of the region. The Tezanos Pinto Formation is the typical loessic unit of the late Pleistocene—early Holocene of the northeastern Pampa region. Advances in the knowledge of the micropaleobotanical content of this geologic formation are presented in this work, especially the obtained results of the Southweastern area of Entre Rios Province. The analyzed phytolith assemblages show a high homogeneity with some variations that allowed their quantitative differentiation across the analyzed sedimentary profiles. The presence of grass phytoliths jointly with palm, podostemoid and ciperoid elements allowe...

Multivariate analysis of modern and fossil pollen data from the central Tianshan Mountains, Xinjiang, NW China

To interpret past vegetation and climate changes from pollen data, we need to reveal the degree of similarity between modern analogues and fossil pollen spectra, which would help us predict the future climate and vegetation. Ninety surface pollen samples across six vegetation zones along an altitudinal gradient from 460 to 3510 m and 44 fossil samples at Caotan Lake were collected in the central Tianshan Mountains, northern Xinjiang, China. Discriminant analyses results, fossil pollen and phytolith assemblages were then used to reconstruct palaeovegetation and palaeoclimate in the area. The 90 surface samples were divided into six pollen zones (alpine cushion, alpine and subalpine meadow, montane Tianshan spruce forest, forest-steppe ecotone, Artemisia desert, typical desert), corresponding to the major vegetation types in the area. These zones follow a climatic gradient of increasing precipitation with increasing elevation. Paleovegetation reconstructed from 44 fossil pollen assemblages through discriminant analysis reflects the regional vegetation shifted from typical desert to Artemisia desert since 4640 cal. year BP in the Caotan Lake wetland. The fossil pollen and phytolith record also reveal the arid climate has not fundamentally changed in the period. But a dry-wet-dry local climate oscillation since 2700 cal. year BP has a fundamental influence on local wetland vegetation dynamics and peat accumulation of the Caotan wetland. Modern wetland landscape and surface pollen assemblages from the Ebinur Lake Wetland Nature Reserve provide further evidence for ferns and Betula growing in the Caotan Lake wetland during the historical period.

Archaeobotanical implications of phytolith assemblages from cultivated rice systems, wild rice stands and macro-regional patterns

Rice can be cultivated in a range of arable systems, including upland rainfed, lowland rainfed or irrigated, flooded or décrue, and deep water cultivation. These agricultural regimes represent ecosystems controlled to large degree by agricultural practices, and can be shown to produce different weed flora assemblages. In order to reconstruct early rice cultivation systems it is necessary to better establish how ancient rice farming practices may be seen using archaeobotanical data. This paper focuses on using modern analogue phytolith assemblages of associated crop weeds found within cultivation regimes, as well as in wild rice stands (unplanted stands of Oryza nivara or Oryza rufipogon), as a means of interpreting archaeobotanical assemblages. Rice weeds and sediment samples have been recorded and collected from a range of arable systems and wild stands in India. The husks, leaves and culms of associated weeds were processed for phytolith reference samples, and sediment samples were processed for phytoliths in order to establish patterns identifiable to specific systems. The preliminary results of the phytolith analysis of samples from these modern fields demonstrate that phytolith assemblage statistics show correlation with variation in rice cultivation systems on the basis of differences in environmental conditions and regimes, with wetness being one major factor. Analysis of phytoliths from archaeological samples from contrasting systems in Neolithic China and India demonstrate how this method can be applied to separate archaeological regions and periods based on inferred differences in past agricultural practices, identifying wet cultivation systems in China, dry millet-dominated agriculture of north China and rainfed/dry rice in Neolithic India.

Phytoliths of Southeastern Vancouver Island, Canada, and their potential use to reconstruct shifting boundaries between Douglas-fir forest and oak savannah

Phytolith assemblages in terrestrial soils have the potential to reveal local shifts between open savannah and conifer forests in the past. On southeastern Vancouver Island, this could help quantify the range of variability of Garry oak savannahs prior to European colonization, and the degree of influence of indigenous people in maintaining open savannahs. We catalogued the phytolith morphotypes found in 72 of the most common plant species in this system, and extracted phytoliths from two soil cores on either side of the boundary between a conifer forest and an oak savannah. Grasses are the most prolific producers of phytoliths in savannahs. In forests, Douglas-fir (Pseudotsuga menziesii) produces large, distinctive asterosclereid phytoliths. Phytolith assemblages from soil cores showed that phytoliths from grasses dominated, even in soils from the forest, where grasses are rare. However, the presence of asterosclereid phytoliths reliably distinguished between Douglas-fir forest and Garry oak savannah habitats within 20m of the vegetation boundary. This finding may be useful for reconstructing past vegetation not only on Vancouver Island, but also across a large geographic area in North America where grasslands tend to be invaded by Douglas-fir following fire suppression. The use of the phytolith record from terrestrial soils at local sites where the history of human occupation is well-known could help establish the degree of influence of indigenous peoples in maintaining open savannahs on southeastern Vancouver Island.

Application of non-grass phytoliths in reconstructing deltaic environments: A study from the Indian Sunderbans

Phytoliths have been proved as reliable indicators of an ecosystem's structure in both modern days as well as in the past. Quantitative phytolith studies from modern plants in India are negligible and most of the data comes from grasses excepting few pteridophytes. Data on non-grass angiospermous phytoliths in India is however completely lacking. In order to interpret the fossil phytolith assemblages and their depositional sub-environments from the deltaic Sunderbans, the largest mangrove vegetation of the world, modern analogue is a prerequisite. The objectives of this study are to establish a relationship between modern deltaic non-grass plant communities of the Indian part of the Sunderbans along salinity gradient with their predominant phytolith contents and this study is the first step in identifying the environment associated with mangrove development from phytoliths in ancient sediments and further studies would ascertain which of these phytoliths would survive erosion and burial. Modern phytolith assemblages were studied from different parts of 33 non-grass species representing 27 genera under 23 families collected from different deltaic sub-environments of the study area. Retrieved leaf phytolith assemblages were subjected to Principal Components Analysis and Cluster Analysis. Elemental analysis of some of these morphotypes done using an Energy Dispersive X-ray Spectrometer (EDX) to authenticate chemical composition of some newly described forms of phytoliths. Twenty five phytolith morphotypes identified under light and Scanning Electron microscopes represent a modern reference non-grass phytolith database of deltaic plant communities of the Sunderbans. Extracted morphotypes are described and their taxonomic and environmental implications are interpreted considering quantitative data and statistical analyses. The taxonomic implications of these morphotypes are mostly poor as observed through both Principal Components Analysis and Cluster Analysis except for monocotyledonous and few dicotyledonous families which produce distinctive morphotypes. However, their role in environmental interpretations could be established using this modern phytolith data. The data would provide a basis for identification of deltaic vegetation of an area using non-grass phytoliths.

Representational bias in phytoliths from modern soils of central North America: Implications for paleovegetation reconstructions

Understanding localized patterns and community compositions of vegetation in an environment is critical to the reconstruction of climatic and ecological conditions across all spatiotemporal scales. One of the most accurate and useful ways to characterize vegetation, and therefore to describe the climatic and ecological conditions of a location, is through the plant fossil record. Phytoliths (plant silica microfossils) are often preserved in the absence of other paleobotanical data and are becoming more widely used for deep-time vegetation reconstructions. Significant work has been done to standardize the analytical methodology of phytolith extraction, statistical analysis, and interpretation, but more detailed investigations are needed to understand how well a given soil assemblage represents the actual aboveground plant biomass for a given ecosystem.We present results from paired soil phytolith assemblages and local vegetation assemblages across the central United States, including temperate forest, grassland, and rangeland/scrubland ecosystems. Phytolith assemblages obtained via extractions from soil A-horizons were compared to percent cover of species and plant biomass estimates obtained via in situ field observations and aerial estimates of tree cover to analyze differences in the relative abundance of forest/woody vegetation vs. grasses. Soil phytolith assemblages from all sites average a 29% bias toward the grass morphotypes as compared to actual aboveground biomass observations, and comparisons to percent cover yielded broadly comparable bias figures. Percent bias estimates do not show significant correlations to most environmental factors (temperature, precipitation, local elevation), however, an extremely strong correlation (p<0.001) was observed with soil order type. This is likely due to the fact that soil order reflects both vegetation type and chemical factors known to affect overall phytolith assemblages; therefore, soil order is a proxy that aggregates several sources of bias. As a result, we suggest further research into the development of correction factors between phytolith sample assemblages and their interpreted past counterpart ecosystems based on estimates derived from modern analyses of each major soil order type. Such background corrections are essential to the continued use of phytoliths as a proxy for past vegetation and ecological reconstructions of temperate ecosystems throughout the Phanerozoic record.

Differentiation of neotropical ecosystems by modern soil phytolith assemblages and its implications for palaeoenvironmental and archaeological reconstructions

The interpretation of Neotropical fossil phytolith assemblages for palaeoenvironmental and archaeological reconstructions relies on the development of appropriate modern analogues. We analyzed modern phytolith assemblages from the soils of ten distinctive tropical vegetation communities in eastern lowland Bolivia, ranging from terra firme humid evergreen forest to seasonally-inundated savannah. Results show that broad ecosystems – evergreen tropical forest, semi-deciduous dry tropical forest, and savannah – can be clearly differentiated by examination of their phytolith spectra and the application of Principal Component Analysis (PCA). Differences in phytolith assemblages between particular vegetation communities within each of these ecosystems are more subtle, but can still be identified. Comparison of phytolith assemblages with pollen rain data and stable carbon isotope analyses from the same vegetation plots show that these proxies are not only complementary, but significantly improve taxonomic and ecosystem resolution, and therefore our ability to interpret palaeoenvironmental and archaeological records. Our data underline the utility of phytolith analyses for reconstructing Amazon Holocene vegetation histories and pre-Columbian land use, particularly the high spatial resolution possible with terrestrial soil-based phytolith studies.

Phytolith taphonomy in the middle- to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)

In semi-arid ecosystems where lacustrine sediments are rare, bio-proxies preserved in fluvial deposits are needed to understand environmental changes. In this study, we evaluate the potential of phytoliths as a bio-proxy in the Yamé River’s deposits at Ounjougou (Mali, West Africa) covering the middle to late Holocene (7790–4000 cal. BP). In soils, phytolith assemblages result mainly from decomposition of local vegetation but in alluvial deposits, the taphonomy of phytoliths is more complex, depending on the type of transport and deposition. In order to define the spatial origin of the phytolith assemblages, either from local (valley floor) or regional vegetation (catchment area), we took the sedimentary characteristics of the deposits into account. Using a combination of general and index approaches, phytoliths of 14 modern and 29 fossil samples from the Yamé valley were analyzed. The predominant source area of represented phytoliths varies with the fluvial energy of transport. Channel deposits, carried during periods of strong fluvial activity, contain higher numbers of savanna grass phytoliths and display a lower ratio of dicotyledon versus Poaceae phytoliths (D/P) than those deposited in the floodplain where phytoliths from the local gallery forest are more strongly represented. From the 5th millennium BP onwards, higher percentages of grass short cell phytoliths (GSCP) and lower D/P values point to gradual vegetation opening due to increasing aridity. High amounts of burned phytoliths show regular fire incidence in the gallery forest and attest for human impact on the landscapes of Ounjougou from the 7th millennium BP onwards. After 4500 cal. BP, there is evidence for pearl millet cultivation.

Ungulate diets reveal patterns of grassland evolution in North America

Equids from the late Miocene (Hemphillian North American Land Mammal Age) of Texas evolved C4 dominated diets earlier than their Nebraska counterparts, leading researchers to hypothesize a northward expansion of C4 grasses between 8 and 6Ma. However, competing hypotheses from multiple paleoecological proxies support one of three hypotheses: that northward C4 expansion occurred at the expense of C3 woodlands, C3 grasslands, or was not occurring during the Hemphillian. We test these alternative hypotheses by comparing the ecosystems of Hemphillian Texas and Nebraska (6.3–7.5Ma) using hoofed mammal dietary reconstruction (hypsodonty and digestive strategy) and by incorporating published tooth enamel isotopes, paleosol isotopes, and phytolith assemblage data. We also use hypsodonty, mesowear, and microwear in a detailed comparison of two localities that are roughly contemporary (Cambridge, Nebraska at 7Ma and Coffee Ranch, Texas at 6.6Ma) to rule out time averaging as an explanatory variable. Through analogy with modern African communities, we reconstruct Texas and Nebraska ecosystems as bushland and woodland, respectively. Using the proportions of hypsodont taxa we estimate mean annual precipitation values of 1217mm/year for Nebraska and 1368mm/year for Texas. Using rarefaction we also do not find differences in the richness of brachydont, hypsodont, and hindgut fermenting taxa. We therefore conclude that both ecosystems were largely similar in hoofed mammal faunal structure during the late Miocene. When compared to published paleosol and phytolith data, which show no differences in C3/C4 biomass among latitudes, our results allow us to reject hypotheses of northward C4 expansion during the late Miocene. We therefore suggest that the equid enamel isotopes may have been biased by two potential factors: the primary reliance on a single locality of appropriate age and possible behavioural lag in C4 feeding among Nebraska equids. These results suggest that the formation of a modern C3/C4 latitudinal gradient occurred later than is previously suggested by equid enamel carbon isotopes.

Paleosols at the Kawakawa tephra isochron: their use in paleoenvironmental reconstruction for northern South Island, New Zealand

The timing of the rise of C4 grasses and the climatic conditions driving their expansion are widely debated, with recent studies suggesting that the expansion was more complex than previously thought. Proxy reconstructions from northwestern Argentina record multiple increases and decreases in C4 abundance throughout the late Miocene to early Pliocene, as well as variations in the timing of the spread of C4 grasses into the region. Here we present a multi-proxy paleovegetation reconstruction of the proportions of C3 and C4 vegetation using organic carbon and phytoliths preserved in paleosols at Entre Ríos in the Santa María Basin of Catamarca, Argentina between 6.2 and 3.3 Ma. Both δCorg13 and phytolith assemblages indicate a C3 dominated ecosystem with no evidence for substantial amounts of C4 vegetation from the late Miocene through mid-Pliocene, despite their rise to dominance elsewhere during this time. These data suggest that by 6.2 Ma the Santa María basin floor was at an elevation high enough to create locally cool conditions that allowed C3 vegetation to outcompete C4 grasses. Phytolith assemblages show that later uplift of the Sierra Calchaquies and Sierra Aconquija ranges through the Pliocene increased aridity and drove the expansion of C3 grasses at the expense of palms and other forest indicators. This multi-proxy paleovegetation reconstruction demonstrates that tectonics played an important role in controlling the late Miocene expansion C4 grasses by suppressing their spread into northwest Argentina.

Comparative phytolith analysis of Festuca (Pooideae: Poaceae) species native to Tierra del Fuego, Argentina

Festuca L. is one of the most representative native grasses of Tierra del Fuego in the southernmost area of South America. In several patches, however, domestic cattle have overgrazed, causing loss or replacement by exotic and adventitious species. We have carried out a comparative phytolith analysis of Patagonian fescue present in the Province of Tierra del Fuego. Fescue leaves are characterized by the presence of truncated cones, crescents, and sinuate trapezoid elements, predominantly short ones. Fan-shaped, small elongated prismatic, and point-shaped phytoliths, as well as articulated phytoliths originating in vascular and epidermal tissues, were observed less frequently. The most common articulated elements in leaf ashes are long cells and a combination of sinuate trapezoid and long cells or crescents. In inflorescence ash assemblages, long cells with undulate borders in association with crescents or emerging hooks are predominant. We have analyzed the diagnostic and differential characteristics of each species of phytolith assemblages to provide information for further studies on the presence of this species in different past soil samples.

Early Pleistocene landscapes and the colonization of Europe

The paleoecological context of hominin occupation in South Asia during the early and middle Pleistocene is virtually unknown. Attirampakkam, India, is an archeological site of global importance, with an early Acheulian occupation (age bracket of ~ 1.07–1.77 Ma) succeeded by Middle Paleolithic levels. Here we report on the recovery of phytoliths from artifact-bearing Quaternary deposits in excavated trenches. We focus on the reconstruction of past vegetation during hominin occupation of the site. The present study provides information on hominin microenvironments and local habitats in South Asia, situating them in a more tangible ecological context than so far achieved. Results show that this region was arid during the earlier stages of the early Pleistocene, and was occupied by hominins living in a landscape locally lacking woody plants. Herbaceous vegetation was dominated by C4 Chloridoid grasses. In the later phase of the early Pleistocene, the landscape was wooded and dominated by C4 Panicoid grasses, with a significant reduction of C4 Chloridoid grasses indicating a shift from a drier to a relatively more humid climate. A diverse husk and leaf phytolith assemblage of wild Oryza spp. (rice) occurring as natural annual or perennial components of the vegetation in the area, other herbaceous plants such as Cyperaceae (sedges), and the continuous presence of blackened phytoliths, suggest the establishment a grassland landscape with enclaves of wetland habitat affected by seasonal flooding and frequent fires. The transition from the early to the middle Pleistocene was marked by a moderately humid climate, with a shift toward aridity during the late Pleistocene, during which we note an environment dominated by C4 Chloridoid grasses, by a sharp reduction of C4 Panicoid grasses, and by a rise in woody taxa. During the middle to late Pleistocene, Middle Paleolithic populations would have witnessed water bodies near the site, as reflected by the presence of plants adapted to swampier conditions such as Cyperaceae and Oryza spp. The archeological record terminates in Layer 1, when human occupation decreased drastically, possibly because of increased aridity and/or greater environmental variability. The phytolith fingerprint at ATM sheds light on the co-occurrence of, vegetation, fire and early prehistoric land occupation. An important aspect is the evidence of Oryza spp., suggesting that wild rice occurred in the environment frequented by these early hominins.

Phytolith variability in Zingiberales: A tool for the reconstruction of past tropical vegetation

Reconstructing paleovegetation is an important part of understanding ancient ecosystems. Phytoliths are preserved even when other fossil evidence (pollen, macrofossils) is not, and can provide evidence for the diversity and distribution of taxa or vegetation that may otherwise have a poor fossil record. Understanding the range of morphologies within plants will help provide better paleovegetation inferences and paleoecological reconstructions. Groups such as the gingers and their relatives (Order Zingiberales) can be ecologically informative and have been used as indicators of frost-free environments. Phytolith morphology in Zingiberales was surveyed from vegetative and reproductive organs of 36 genera and all eight extant families and from the extinct taxon Spirematospermum. Druse, trough, and hat-shape phytoliths are found in vegetative organs and are diagnostic at the family level, while seed phytoliths consistently differ from vegetative material and are highly variable. Druses are produced by Cannaceae, Costaceae, Strelitziaceae, and rarely by Marantaceae. Troughs are produced by Heliconiaceae and Musaceae and the two families are distinguishable by the depth of the central concavity. Hat-shaped morphotypes are found in Lowiaceae and Marantaceae, with those of Lowiaceae being larger in size. Zingiberaceae largely produced silica sand. Marantaceae phytoliths were variable. Globular and tabular morphotypes are among the least diagnostic and are produced in some form in most families. Spirematospermum produced silica sand. Phytoliths suggest that Spirematospermum is most closely related to Zingiberaceae, and not to Musaceae. These results provide support for distinguishing between zingiberalean families. Recognition of these morphotypes in fossil phytolith assemblages can provide evidence for (sub)tropical vegetation and distinctions can be made between microhabitats such as moist, high-light forest gaps vs. shaded understory, with the potential to produce more nuanced paleovegetation reconstructions.

Phytoliths from the coastal savannas of French Guiana

Phytolith reference collections are a fundamental prerequisite for accurate interpretation of fossil phytolith assemblages used in reconstructing vegetation histories. As part of a multi-disciplinary research project studying Late Holocene landscape transformations associated with pre-Columbian raised field complexes in the coastal savannas of French Guiana, phytolith production in selected plant species with high environmental and economic significance native to the region was examined. A total of 49 families, 92 genera, and 108 species were analysed. Phytolith abundance in each specimen was rated qualitatively and morphotypes described following modern standards of nomenclature. Of the 92 non-Poaceae species tested, 37 contributed phytoliths that are diagnostic to at least the family level. Two of these are newly-discovered phytolith morphotypes isolated from Protium guianense (Burseraceae) and Thelypteris confluens (Thelypteridaceae [Pteridophyta]) which have not been described previously. This work represents the first systematic undertaking to establish a phytolith reference collection of French Guiana flora. Results reinforce the usefulness of phytolith analysis for distinguishing ecologically significant taxa, and therefore major vegetation formations. The creation of a comprehensive reference collection for French Guiana improves taxonomic resolution and has provided the necessary ground work for the interpretation of palaeoevironmental and archaeological records in the region.

Paleoenvironment of the Toropí Formation (Upper Pleistocene), Corrientes province (Mesopotamian region, Argentina): A phytolith approach

Two Pleistocene sedimentary units are recognized in the Corrientes province, Argentina: the Toropí and Yupoí formations. These sediments have proven productive for fossil vertebrates, but few macrofossils have been recovered. To remedy this situation, plant silica (phytoliths) were extracted from the sediments, enabling a direct comparison of paleovegetation data and information based on previous study of vertebrates. The studied samples (n = 28) come from two profiles from the Toropí Stream (28°36′S; 59°02′W), near Bella Vista, Corrientes, from which two Quaternary mammals, Lestodon (Xenarthra) and Hippocamelus (Artiodactyla), have previously been excavated. All samples were productive and contained both non-plant biogenic silica (diatoms, sponge spicular, chrysophyte cysts) and phytoliths. Phytolith assemblages were dominated by morphotypes diagnostic of grasses, in particular C3 pooids, C4 chloridoids, and C3 or C4 panicoids (or related grasses in the PACMAD clade). Rare phytoliths of palms and other woody or herbaceous dicotyledonous angiosperms were also present. This combination of C3 and C4 grasses, and rare palms and other forest indicators, indicates grass-dominated habitats with groves with palms and other trees/shrubs along rivers, growing under a relatively warm and dry climate. This mixed plant community reflects shifting biogeographic affinity with the Chaco-Pampean plain and inter-tropical regions, respectively, linked to the frequent climatic-environmental fluctuations during the Late Pleistocene.

Eocene vegetation and ecosystem fluctuations inferred from a high-resolution phytolith record

A thorough understanding of the ecosystem factors that can act as drivers of vegetation change, an important factor for projecting impacts of future climate change, requires adequately distinguishing between plant community changes that occur on the local scale or over ecological time scales, and long-term trends. Phytolith assemblages have the potential to provide this information, but little work has been done so far to test their ability to do so in deep time. We examined vegetation patterns inferred from phytoliths (plant silica microfossils) from a single section of the Renova Formation, Timberhills region, Montana, dated to 39.2 ± 3 Ma (late middle Eocene). The section is composed of fl uvial sediments overprinted by paleosols including Alfi sols, Entisols, Inceptisols, and composite paleosols. Phytolith assemblages from 27 paleosol samples were used to reconstruct a high-resolution vegetation history for the area and were compared with paleosol data. Phytoliths are predominantly from forest plants and include tropical elements such as palms (Arecaceae) and gingers (Zingiberales), suggesting a paratropical forest . The high-resolution sampling records heterogeneous vegetation including shifts among closed forest, moderately open forest (forest gaps, edges, and woodland), and grass-dominated habitats. Grasses are interpreted as early open-habitat plants tolerant of drier conditions, but they appear to be replaced by forest vegetation with time, resulting in poor correspondence between paleosol type and phytolith assemblage at some stratigraphic levels, where paleosol morphology indicates a forest ecosystem and the phytolith assemblages indicate a changing grass-forest mixture as a function of depth within the profi les. This is the fi rst study that has used phytoliths to construct a high-resolution record of vegetation from deep time, and we demonstrate that dense sampling and multiproxy approaches to paleo environmental reconstruction are necessary to capture vegetation heterogeneity in time and across microhabitats.

Experimental investigation of pathogenic stress on phytolith formation in Cucurbita pepo var. texana (wild gourd)

Silica phytoliths that form in plant tissues are useful to archaeologists because of their diagnostic value and longevity in ancient deposits. Palaeoecology, site formation processes, plant domestication, and other topics are routinely addressed using phytolith assemblages, especially when macrobotanical remains are not well preserved. However, little research has been conducted to document the effects of ecological variables on phytolith formation. Here, we investigate the effects of mosaic virus and bacterial wilt disease on diagnostic scalloped phytoliths in the rind of a wild-type Cucurbita pepo var texana (gourd). We observe a minimal change in phytolith size distribution between control plants and individuals with mosaic virus. However, we observe a notable difference between plants with bacterial wilt disease and control plants, with diseased individuals carrying a greater proportion of large-diameter scalloped phytoliths. This and similar phenomena could potentially confound archaeological interpretations of phytolith assemblages, and we suggest that the effects of this and other ecological variables should be studied in a diverse range of taxa.

Geoarchaeology and Paleoenvironmental Context of the Burntwood Creek Rockshelter, High Plains of Northwestern Kansas, U.S.A

The first systematic geoarchaeological study of a rockshelter in Kansas yielded information about rockshelter formation, Holocene paleoenvironments, archaeological site formation processes, and prehistoric human habitation and site use. The rockshelter was carved by groundwater sapping; colluvium, alluvium, and roof‐fall debris subsequently accumulated on its floor. An assemblage of Late Archaic (∼2000–4000 14C years before present [yr B.P.]) cultural deposits (lithic material, bone, and charcoal) is preserved in a 2‐m thick package of colluvium and alluvium in front of the shelter. Chipped stone analysis indicates that Late Archaic occupants of the shelter were using mostly local materials and resharpening their stone tools at the shelter. Stable carbon isotope and phytolith analyses indicate that a mixed C3 and C4 plant community existed in the study area and that it changed in composition through the late Holocene. Based on the phytolith assemblage from an unlined fire pit at the front of the shelter, Late Archaic people used local hackberry trees for fuel and/or food.

C3 Poaceae and Restionaceae phytoliths as potential proxies for reconstructing winter rainfall in South Africa

The main objective of this research is to identify graminoid phytolith morphotypes with potential as proxies for reconstructing past winter rainfall in South Africa. The main argument of this study is that phytolith proxies for winter-rainfall maxima should be found among native graminoids abundant in the Cape Region, where most of the precipitation occurs in the cooler part of the year. Vegetation surveys indicate that C3 Poaceae (cool-season grasses) and Restionaceae (restios) are abundant graminoids in the winter rainfall zone (WRZ). Therefore, the frequencies of diagnostic graminoid morphotypes of each of these two groups are correlated independently with both percent and amount of winter rainfall (defined here as the sum of April-September precipitation). The phytolith assemblages used for this study were collected from soils along two transects across the winter (WRZ), all-year (ARZ), and summer (SRZ) rainfall zones of South Africa.The study shows that the highest frequencies of the diagnostic C3 grass silica short-cell (GSSC) morphotypes increase with winter rainfall. Although considerable numbers of C3-GSSC morphotypes occur in samples at elevation above 1500m in the SRZ, their frequencies are lower than in the samples of the WRZ and ARZ. Correlation is noteworthy only when all the C3-GSSC morphotypes are grouped. Individual C3-GSSC morphotypes and groups of GSSC morphotypes linked to particular C3 grass subfamilies (Pooideae, Ehrhartoideae and Danthonioideae) correlate poorly with winter rainfall incidence. The results of this study also suggest that Restionaceae phytoliths are good indicators of winter rainfall, but because Restionaceae occur mainly in oligotrophic soils in association with fynbos vegetation, the use of their phytoliths in paleorainfall reconstruction should be taken with care. Despite certain limitations, this research shows that the use of C3-GSSC and Restionaceae phytolith has a strong potential for reconstructing the extent of winter rainfall during the colder stages of the Pleistocene. However, to achieve this objective a study with a larger number of reference material and tighter geographical sampling is needed.