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Long-Term Records of Vegetation Dynamics As a Basis for Ecological Hypothesis Testing

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Long-Term Records of Vegetation Dynamics As a Basis for Ecological Hypothesis Testing Perspectives in Plant Ecology, Evolution and Systematics 15 (2013) 338–359 Contents lists available at ScienceDirect Perspectives in Plant Ecology, Evolution and Systematics jo urnal homepage: www.elsevier.com/locate/ppees Review Ecological palaeoecology in the neotropical Gran Sabana region: Long-term records of vegetation dynamics as a basis for ecological hypothesis testing a,∗ b c,d Valentí Rull , Encarni Montoya , Sandra Nogué , e a,e Teresa Vegas-Vilarrúbia , Elisabet Safont a Palynology & Paleoecology Lab, Botanic Institute of Barcelona (IBB-CSIC-ICUB), Pg. del Migdia s/n, 08038 Barcelona, Spain b Department of Environment, Earth & Ecosystems, Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR), The Open University, Walton Hall, Milton Keynes MK7 6AA, UK c Long-term Ecology Laboratory, Biodiversity Institute, Department of Zoology, University of Oxford, Tinbergen Building, South Parks Road, Oxford OX1 3PS, UK d Department of Biology, University of Bergen, N-5020, Bergen, Norway e Department of Ecology, University of Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain a r t i c l e i n f o a b s t r a c t Article history: Long-term palaeoecological records are needed to test ecological hypotheses involving time, as short- Received 18 March 2013 term observations are of insufficient duration to capture natural variability. In this paper, we review the Received in revised form 27 July 2013 published palaeoecological evidence for the neotropical Gran Sabana (GS) region, to record the vege- Accepted 29 July 2013 tation dynamics and evaluate the potential effects of natural climatic and anthropogenic (notably fire) Available online 19 September 2013 drivers of change. The time period considered (last 13,000 years) covers major global climate changes and the arrival of humans in the region. The specific points addressed are climate–vegetation equilib- Keywords: rium, reversibility of vegetation changes, the origin of extant biodiversity and endemism patterns and Long-term ecology biodiversity conservation in the face of global warming. Vegetation dynamics is reconstructed by pollen Non-analogue communities analysis and fire incidence is deduced from microscopic charcoal records. Palaeoclimatic inferences are Community stability Climate–vegetation disequilibrium derived from global and regional records using independent physico-chemical evidence to avoid circular Origin of biodiversity reasoning. After analyzing all the long-term records available from both GS uplands and highlands, we Biodiversity conservation conclude that: (1) Upland vegetation (mostly treeless savannas and savanna–forest mosaics, with occa- sional Mauritia palm swamps) is not in equilibrium with the dominant climates, but largely conditioned by burning practices; (2) a hypothetical natural or “original” vegetation type for these uplands has not been possible to identify due to continuous changes in both climate and human activities during the last 13,000 years; (3) at the time scale studied (millennial), the shift from forest to savanna is abrupt and irreversible due to the existence of tipping points, no matter the cause (natural or anthropogenic); (4) on the contrary, the shift from savanna to palm swamps is reversible at centennial time scales; (5) some of the reconstructed past vegetation types have no modern analogues owing to the individual species response to environmental shifts, leading to variations in community composition; (6) extant biodiver- sity and endemism patterns are not the result of a long history of topographical isolation, as previously proposed but, rather, the consequence of the action of climatic and palaeogeographic variations; (7) the projected global warming will likely exacerbate the expansion of upland savannas by favouring positive fire-climate feedbacks; (8) in the highlands, extinction by habitat loss will likely affect biodiversity but to a less extent that prognosticated by models based only on present-day climatic features; (9) future highland communities will likely be different to present ones due to the prevalence of individual species responses to global warming; and (10) conservation strategies at individual species level, rather than at community level, are enriched by long-term palaeoecological studies analyzed here. None of these conclusions would have been possible to derive from short-term neoecological observations. © 2013 Elsevier GmbH. All rights reserved. ∗ Corresponding author. Tel.: +34 93 2890611. E-mail address: vrull@ibb.csic.es (V. Rull). 1433-8319/$ – see front matter © 2013 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.ppees.2013.07.004 V. Rull et al. / Perspectives in Plant Ecology, Evolution and Systematics 15 (2013) 338–359 339 Contents Introduction . 339 Ecological palaeoecology and the Gran Sabana . 339 The origin of upland savannas . 339 The role of fire. 341 The origin of highland biodiversity and endemism . 341 Aims and temporal scope . 341 Study area. 342 Geology, geomorphology and soils . 342 Climate . 342 Vegetation . 342 Human occupancy . 343 Methods. 344 Sites and general procedures . 344 Pollen analysis . 344 Charcoal analysis . 344 Palaeoclimatology. 344 Long-term patterns of vegetation change . 345 Forest–savanna dynamics . 345 Savanna–morichal dynamics . 346 Non-analogue communities . 347 Elevational migration . 348 Community stability through time . 349 Discussion. ..
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