Franck Vautier

Forest Invasion by the African Tulip Tree (Spathodea campanulata) in the Hawaiian Islands: Are Seedlings Shade-Tolerant?

Abstract: Native to West Africa, Spathodea campanulata (African tulip tree) is frequently viewed as a shade-intolerant invader. It commonly colonizes roadsides, human-disturbed forests, and abandoned agricultural land in tropical islands, where it can then become dominant in secondary forests. Some authors have suggested that the seedlings may be shade-tolerant and able to establish in closed-canopy forest, but the shade tolerance of seedlings has never been evaluated. We identified tolerated light environments of S. campanulata seedlings in wet forests in Hawai‘i by measuring photosynthetically active radiation (PAR) around naturally occurring seedlings (<30 cm height) in the field. We also measured photosynthetic responses of seedlings to light under field and laboratory conditions and determined seedling growth rates in sun and shade. Seedlings were found in shaded conditions in the field, and they consistently had positive net carbon gain at 50 µmol photons m-2.sec-1 PAR, with an estimated mean compensation point below 10 µmol photons m-2.sec-1, indicating high shade tolerance. The most frequent midday light environments of S. campanulata seedlings in the field were in the range of 50 to 200 µmol photons m-2.sec-1 PAR (i.e., 2.5% to 10% of full sunlight). Among seedlings found growing in shade, minimum saturating light (Ek), determined from chlorophyll fluorescence, averaged 260 µmol photons m-2.sec-1, suggesting that maximum seedling photosynthesis can occur at less than 13% of full sun. Growth rates of young seedlings in shade and sun were comparable. Widespread wind dispersal of seeds, seedling tolerance of low light, and our observations of some S. campanulata saplings establishing in rain forest without recent disturbance suggest that S. campanulata will be a persistent component of Hawaiian lowland rain forests.

First Sculpted Human Face in the Western Mediterranean Early Neolithic

The development of the Neolithic way of life in the western Mediterranean during the sixth millennium cal. BC is the consequence of the spread of populations from the Near East after successive stages of cultural remodelling. Despite the clear contribution of the Near Eastern and Aegean Neolithic to the economic and technical changes that happened to the west, little is known here about their symbolic legacies, because of the scarcity of representations and ritual evidences associated to the earliest western Neolithic contexts. Excavations at the rock shelter of Pendimoun (southeastern France) yielded the first anthropomorphic stone sculpture from the western Mediterranean Neolithic (early sixth millennium cal. BC). Using both carving and painting techniques, it represents a realistic-looking human face and is a unique example within the western Mediterranean and European frameworks. After describing the shaping and colouring details of the mask, the authors here deal with its possible social significances and cultural connections.

The Highest Gradient Model: A New Method for Analytical Assessment of the Efficiency of LiDAR-Derived Visualization Techniques for Landform Detection and Mapping

ALS-derived raster visualization techniques have become common in recent years, opening up new possibilities for subtle landform detection in earth sciences and archaeology, but they have also introduced confusion for users. As a consequence, the choice between these visualization techniques is still mostly supported by empirical knowledge. Some attempts have been made to compare these techniques, but there is still a lack of analytical data. This work proposes a new method, based on gradient modelling and spatial statistics, to analytically assess the efficacy of these visualization techniques. A selected panel of outstanding visualization techniques was assessed first by a classic non-analytical approach, and secondly by the proposed new analytical approach. The comparison of results showed that the latter provided more detailed and objective data, not always consistent with previous empirical knowledge. These data allowed us to characterize with precision the terrain for which each visualization technique performs best. A combination of visualization techniques based on DEM manipulation (Slope and Local Relief Model) appeared to be the best choice for normal terrain morphometry, occasionally supported by illumination techniques such as Sky-View Factor or Negative Openness as a function of terrain characteristics.

Historical fluvial palaeodynamics and multi-proxy palaeoenvironmental analyses of a palaeochannel, Allier River, France

A palaeoenvironmental study of a palaeochannel within the lower alluvial floodplain of the Allier River, France, has been carried out at a high temporal resolution. Research was based upon a multi-proxy approach using different sedimentological (magnetic susceptibility, sediment texture and loss on ignition) and palaeoecological (pollen, non-pollen palynomorphs (NPPs), diatoms – indicators). The palaeochannel was dated from six radiocarbon dates and spans from the second to the eleventh century AD. The cultural landscape history of this floodplain and the progressive hydrological disconnection of the palaeochannel between the Antiquity and the early Middle Ages could be reconstructed according to several characteristic environmental phases. Co-inertia analysis linking pollen, NPPs and diatom corroborated the significant co-structure of these proxies and allowed to distinguish functional palaeoecological groups in terms of landscape openness, on-site aquatic and hygrophilous vegetation, riparian woodland, soil moisture and grazing pressure. Results obtained underpin the importance of grazing as a major agent of landscape change in floodplains, especially since the ninth century AD, when the clearance of the riparian woodland is attested. Gallo-Roman and Late-Antiquity land-use systems, on the contrary, allowed for the preservation of riparian fluvial landscapes.

Impact of cement repointing on rates of sandstone decay in medieval churches of the French Massif Central

Abstract Three Romanesque churches of the Bourbonnais region in the French Massif Central have been investigated. These date back to the twelfth century, and are mainly built of red and white sandstones. Their ashlar blocks were extensively repointed in the mid-twentieth century with cement-rich mortar. In order to quantitatively assess the impact of repointing on the decay rates of the sandstones, the following methods have been used: dating of reference surfaces (‘zero datum levels’) based on stone-dressing marks, stone-by-stone and terrestrial LiDAR (Light Detection And Ranging) surveys, and petrographical analyses including on-site non-destructive tests. This study reveals that, between the twelfth century and the mid-twentieth century, intrinsic geological factors have been a key control on weathering rates. Stone surface recession has proceeded, on average, 500 times faster in the poorly cemented soft white sandstone compared to the iron-cemented red sandstone (4 mm/century v. 0.008 mm/century). Since the mid-twentieth century, the replacement of the original lime mortar with a cement-rich mortar has resulted in a marked increase in weathering rates and resulting surface recession of the poorly cemented white sandstone: this increase is fivefold where cement-lime mortar (‘bastard mortar’) has been used and 10-fold where harder cement-rich mortar has been applied. By contrast, the application of cement-lime mortar between the ashlars composed of iron-cemented red sandstone had no deleterious effects. This study confirms that the use of cement-based mortar should be avoided on soft and porous masonries. It also stresses the fact that accelerated stone surface recession rates are systematically associated with heritage sites that are subject to significant anthropogenic effects caused by inappropriate interventions or excessive pressure on the monuments or their environment.