1,721,177 research outputs found
How dynamic are tropical forests? Long-term human impact drives landscape “hyperdynamism” in an ancient tropical forest
No full textA method for reconstructing temporal changes in vegetation functional trait composition using Holocene pollen assemblages
Full text linkMethods of reconstructing changes in plant traits over long time scales are needed to understand the impact of changing environmental conditions on ecosystem processes and services. Although Holocene pollen have been extensively used to provide records of vegetation history, few studies have adopted a functional trait approach that is pertinent to changes in ecosystem processes. Here, for woody and herbaceous fen peatland communities, we use modern pollen and vegetation data combined with pollen records from Holocene deposits to reconstruct vegetation functional dynamics. The six traits chosen (measures of leaf area-to-mass ratio and leaf nutrient content) are known to modulate species’ fitness and to vary with changes in ecosystem processes. We fitted linear mixed effects models between community weighted mean (CWM) trait values of the modern pollen and vegetation to determine whether traits assigned to pollen types could be used to reconstruct traits found in the vegetation from pollen assemblages. We used relative pollen productivity (RPP) correction factors in an attempt to improve this relationship. For traits showing the best fit between modern pollen and vegetation, we applied the model to dated Holocene pollen sequences from Fenland and Romney Marsh in eastern and southern England and reconstructed temporal changes in trait composition. RPP adjustment did not improve the linear relationship between modern pollen and vegetation. Leaf nutrient traits (leaf C and N) were generally more predictable from pollen data than mass-area traits. We show that inferences about biomass accumulation and decomposition rates can be made using Holocene trait reconstructions. While it is possible to reconstruct community-level trends for some leaf traits from pollen assemblages preserved in sedimentary archives in wetlands, we show the importance of testing methods in modern systems first and encourage further development of this approach to address issues concerning the pollen-plant abundance relationship and pollen source area
Pollen profile LAVPICCO, Lago Piccolo di Avigliana, Italy
No full textThis dataset was archived on 2014-09-12 from the EPD database (http://www.europeanpollendatabase.net)
Lithology of sediment core LAVPICCO, Lago Piccolo di Avigliana, Italy
No full textThis dataset was archived on 2014-11-03 from the EPD database (http://www.europeanpollendatabase.net)
New insights on stomata analysis of European conifers 65 years after the pioneering study of Werner Trautmann (1953)
Full text linkInternational audienceConifer-stomata analysis is an essential part of the palaeoecological toolbox because it allows the determination of the local presence of plant populations with a lower degree of uncertainty than pollen analysis. Although the European postglacial pool of conifer taxa is broad, stomata morphologies for only few taxa have been investigated. Prior stomata morphology studies focused on taxa having wide distribution ranges in central and northern Europe, and stomata morphologies for taxa occurring in southern European and Northern African mountain regions have not yet been described. Here, we present a qualitative assessment of stomata morphologies for 40 taxa from eight genera (Cupressus, Juniperus, Abies, Cedrus, Larix, Picea, Pinus and Taxus) that are present on the European continent and the southern borderlands of the Mediterranean Basin, thereby broadening substantially both the regional and taxonomical coverage of this now 65-years old technique. We found that visual identification of conifer stomata does not allow species-level identifications, supporting the notion of genus-specific stomata morphologies found in prior studies. For each genus, we describe the stomata morphologies taking into account the varying shape of stomata features at different focusing levels. In addition, we provide stop-motion animations (publicly available at http://dx.doi.org/10.6084/m9.figshare.7165261) that may be useful tools for microscope analysts who wish to acquaint themselves with conifer-stomata analysis
Holocene vegetation and land-use changes in response to climatic changes in the forelands of the southwestern Alps, Italy
No full textInternational audienceThe Holocene sediment of Lago Piccolo di Avigliana (Piedmont, Italy, 356 m a.s.l.) was dated by 14C and analysed for pollen to reconstruct the vegetation history of the area. The early‐ and mid‐Holocene pollen record shows environmental responses to centennial‐scale climatic changes as evidenced by independent palaeoclimatic proxies. When human impact was low or negligible, continental mixed‐oak forests decreased at ca. 9300 BC in response to the early‐Holocene Preboreal climatic oscillation. Abies alba expanded in two phases, probably in response to higher moisture availability at ca. 6000 and ca. 4000 BC, while Fagus expanded later, possibly in response to a climatic change at 3300 BC.During and after the Bronze Age five distinct phases of intensified land use were detected. The near synchroneity with the land‐use phases detected in wetter regions in northern and southern Switzerland points to a common forcing factor in spite of cultural differences. Increasing minerogenic input to the lake since 1000 BC coincided with Late Bronze—Iron Age technical innovations and probably indicate soil erosion as a consequence of deforestation in the lake catchment. The highest values for cultural indicators occurred at 700–450 and at 300–50 BC, coinciding with periods of high solar activity (inferred from Δ14C). This suggests that Iron Age land use was enhanced by high solar activity, while re‐occupation of partly abandoned areas after crises in earlier periods match better with the GRIP stable isotope record. On the basis of our data and comparison with independent palaeoclimatic proxies we suggest that precipitation variation was much more important than temperature oscillations in driving vegetation and societal changes throughout the Holocene. Copyright © 2006 John Wiley & Sons, Ltd
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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