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Liège, Belgium

Lim S.,Montpellier University | Ledru M.-P.,CNRS Montpellier Institute of Evolutionary Sciences | Valdez F.,IRD Montpellier | Devillers B.,Montpellier University | And 4 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2014

The La Tolita archeological site is located in the Province of Esmeraldas in the northwestern part of Ecuador at the border with Colombia. This area comprises one of the world's wettest coastal regions with mangrove and swamps along the coast and has one of the richest tropical rainforest of the planet, extending inland. Today this region is seriously affected by natural hazards including earthquakes, deposition of thick layers of volcanic ash, tsunamis, and El Niño flooding. The region also hosted one of the most important and famous cultures of the late Holocene, the La Tolita-Tumaco, which dominated northern South America between 2900 and 1100. yr BP. With the aim of characterizing the influence on the environment of the different factors of natural hazards, climate changes, and human activities, we drilled a 4-m long sediment core in a swamp close to the La Tolita site. The record dates back to 5000. years BP. Multiproxy analyses of pollen, microcharcoal, XRF-based geochemical data, and geochronology were performed on the sediment to distinguish the different drivers of change. At ~. 3000. yr BP, an earthquake dramatically modified the landscape, elevating the ground and changing the course of the rivers. In the following two millennia until 1100. yr BP, raised-field agricultural activities dominated the site, providing evidence for an increase in the local population. Human activity progressively declined after 1100. yr BP, with the loss of the regional influence of the Tolita culture. The climate remained permanently moist throughout the sediment record, both the rainforest and the mangrove remained well developed, and marine incursions were short and frequent. © 2013 Elsevier B.V. All rights reserved.

Saltre F.,Institute Of Botanique | Saltre F.,Oregon State University | Bentaleb I.,Montpellier University | Favier C.,Montpellier University | Jolly D.,Montpellier University
Climatic Change | Year: 2013

Paleo-data suggest that East African mountain treelines underwent an altitudinal shift during the Last Glacial Maximum (LGM). Understanding the ecological and physiological processes underlying treeline response to such past climate change will help to improve forecasts of treeline change under future global warming. In spite of significant improvements in paleoclimatic reconstruction, the climatic conditions explaining this migration are still debated and important factors such as atmospheric CO2 concentration, the impact of lapse rate decreasing temperature along altitudinal gradients and rainfall modifications due to elevation have often been neglected or simplified. Here, we assess the effects of these different factors and estimate the influence of the most dominant factors controlling changes in past treeline position using a multi-proxy approach based on simulations from BIOME4, a coupled biogeography and biogeochemistry model, modified to account for the effect of elevation on vegetation, compared with pollen, and isotopic data. The results indicate a shift in mountain vegetation at the LGM was controlled by low pCO2 and low temperatures promoting species morphologically and physiologically better adapted to LGM conditions than many trees composing the forest belt limit. Our estimate that the LGM climate was cooler than today's by -4.5 °C (range: -4.3 to -4.6 °C) at the upper limit of the treeline, whereas at 831 m it was cooler by -1.4 °C (range: -2.6 to -0.6 °C), suggests that a possible lapse rate modification strongly constrained the upper limit of treeline, which may limit its potential extension under future global warming. © 2013 Springer Science+Business Media Dordrecht.

Fowler A.M.,University of Auckland | Boswijk G.,University of Auckland | Lorrey A.M.,NIWA - National Institute of Water and Atmospheric Research | Gergis J.,University of Melbourne | And 5 more authors.
Nature Climate Change | Year: 2012

It is not known how global warming will affect the El Nià ±o/Southern Oscillation (ENSO). The instrumental record is too short to discern centennial-scale trends and modelling results are inconclusive. Proxy reconstructions indicate that ENSO activity was relatively high during the late twentieth century, but whether this was unusual in the millennial context remains uncertain. Here we present insights into these issues derived from rings of the kauri tree (Agathis australis), a rare long-lived conifer endemic to the forests of northern New Zealand. Our results indicate that the twentieth century was the most 'ENSO-active' century of the past 500 years, but may not be unique in the context of the past 700 years, and that ENSO activity comparable to or elevated above that experienced during the late twentieth century is plausible under warmer-than-present conditions. We also find evidence that there may have been significant changes in the ENSO teleconnection to the New Zealand region during the fourteenth and fifteenth centuries, and of multi-decadal fluctuations in ENSO-related activity building up to the present day. Although these two features may delay the expression of increased ENSO activity in the New Zealand region, our results indicate that New Zealand climate is likely to be more dominated by ENSO-related inter-annual variability as the world continues to warm. © 2012 Macmillan Publishers Limited. All rights reserved.

Frejaville T.,National Research Institute of Science and Technology for Environment and Agriculture | Frejaville T.,EPHE Paris | Curt T.,National Research Institute of Science and Technology for Environment and Agriculture | Carcaillet C.,EPHE Paris | Carcaillet C.,Institute Of Botanique
Frontiers in Plant Science | Year: 2013

Relationships between the flammability properties of a given plant and its chances of survival after a fire still remain unknown. We hypothesize that the bark flammability of a tree reduces the potential for tree survival following surface fires, and that if tree resistance to fire is provided by a thick insulating bark, the latter must be few flammable. We test, on subalpine tree species, the relationship between the flammability of bark and its insulating ability, identifies the biological traits that determine bark flammability, and assesses their relative susceptibility to surface fires from their bark properties. The experimental set of burning properties was analyzed by Principal Component Analysis to assess the bark flammability. Bark insulating ability was expressed by the critical time to cambium kill computed from bark thickness. Log-linear regressions indicated that bark flammability varies with the bark thickness and the density of wood under bark and that the most flammable barks have poor insulating ability. Susceptibility to surface fires increases from gymnosperm to angiosperm subalpine trees. The co-dominant subalpine species Larix decidua (Mill.) and Pinus cembra (L.) exhibit large differences in both flammability and insulating ability of the bark that should partly explain their contrasted responses to fires in the past. © 2013 Frejaville, Curt and Carcaillet.

Pagnoux C.,Paris-Sorbonne University | Pagnoux C.,Institute Of Botanique | Bouby L.,Institute Of Botanique | Ivorra S.,Institute Of Botanique | And 6 more authors.
Vegetation History and Archaeobotany | Year: 2014

The origins and biogeographical history of Vitis vinifera L. (domesticated grapevine) remain largely unknown. Shape and size have long been used as criteria to distinguish between wild and domesticated grape pips. Here we have analyzed variations of seed morphology in order to provide accurate criteria for the discrimination of different groups of varieties. Diversity in present-day cultivars and wild grapevines of Greek and east Mediterranean origin in relation to other Asiatic and European varieties and wild grapevines provides the basis for our analysis, which aims to allow the characterization of the ancient diversity of cultivated grapes in relation to present-day cultivars. Geometric morphometric analyses (Elliptic Fourier Transform method) have been used to characterize the seed shape and size of modern and archaeological material using 40 variables per seed. 197 archaeological grape pips from the 7th century bc sanctuary of Hera in Samos, Greece were compared with an extended reference collection of 269 modern cultivars and 83 wild populations, 10,518 seeds in total. Our study confirms the relationships between seed shape and domestication. Modern diversity is partly structured by the geographical origin of cultivars, but influence of other factors may play a significant role in clustering. The wide diversity of varieties offered at the Heraion of Samos during the Archaic Period, including cultivars growing on the island, imported grapes and wild morphotypes, is related to the history and geographical location of the island as well as to the diversity in the geographical range of pilgrims making offerings to the sanctuary. © 2014 Springer-Verlag Berlin Heidelberg.

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