Plant communities and species richness of the calcareous grasslands in southeast Belgium

in Belgian Journal of Botany (2007), 140(2), 157-173

Calcareous grasslands are biodiversity hotspots in Western Europe. In Belgium, a number of phytosociological surveys have been realized in these habitats, but none covers the whole range of calcareous ... [more ▼]

Calcareous grasslands are biodiversity hotspots in Western Europe. In Belgium, a number of phytosociological surveys have been realized in these habitats, but none covers the whole range of calcareous grasslands at the regional scale. The aim of this study was (i) to provide a synthesis of the floristic variation of calcareous grasslands of the Calestienne natural region using a uniform methodology; (ii) to relate floristic variation to environmental variables, and (iii) to characterize the specific diversity of the different grassland communities that occur in the study region. Seven different communities were identified with the TWINSPAN method. The originality of the grasslands on calcareous and calcareo-siliceous rocks was statistically confirmed. Significant differences for environmental variables were identified among the seven communities by a MANOVA. Main differences between communities were related to xericity and pH, although a north-south gradient was also identified. More xeric grasslands were located in the southern part of the study region while northern part was occupied by more mesophilous grasslands. Multiple regressions were used to describe the influence of the environmental conditions on plant species richness. The most mesophilous grasslands appeared to be the most species-rich while soil acidity negatively affected species richness. [less ▲]

Appui scientifique à la mise en œuvre de réseau Natura 2000 en Wallonie: Finalisation de la typologie WALEUNIS et synthèse des états de conservation, critères de restauration et mesures de gestion pour les habitats semi-naturels ouverts. Rapport final

Report (2006)

Bimodal pollination system in rare endemic Oncocyclus irises (Iridaceae) of Lebanon

in Canadian Journal of Botany (2006), 84(8), 1327-1338

Pollination systems based on indirect rewards, such as heat and shelter, have seldom been studied. Plant-pollinator interactions were characterized in Iris cedretii Dinsmore ex Chaudhary and Iris sofarana ... [more ▼]

Pollination systems based on indirect rewards, such as heat and shelter, have seldom been studied. Plant-pollinator interactions were characterized in Iris cedretii Dinsmore ex Chaudhary and Iris sofarana subsp. kasruwana Dinsmore ex Chaudhary, rare endemic Lebanese Oncocyclus irises exhibiting potential adaptation to shelter pollination. Despite a diversity of floral visitors (47 species), only two groups of Anthophoridae male bees (Xylocopa spp. and Eucera spp.) could be considered as efficient pollinators on the basis of frequency of visits, visiting behaviour, and pollen load. Lebanese Oncocyclus irises showed a bimodal pollination system with (1) diurnal visits at low rates but with potentially large pollen transfers by Xylocopa bees, exhibiting a foraging-like behaviour, principally during warm periods of the day and (2) sheltering, especially Eucera male bees, during night and day when the weather is changeable. Refuge occurrence in flowers was more important during the night (27%) than during the day (12%) and, for daytime, during cloudy or windy than sunny conditions. It also varied depending on the exposure of floral tunnels. Visitation rates of both day-visiting Xylocopa and night-sheltering Eucera were negatively associated with an increase of the number of flowers per clump. No experimental evidence was found showing that the principal advantage for male bees to shelter in Iris flowers was to fly earlier in the morning. [less ▲]

Within-population genetic structure and clonal diversity of Viola calaminaria, an endemic metallophyte

Conference (2006)

Mise en place d'une structure venant en appui à la msie en oeuvre méthodologique et technique de la méthode agri-environnemetale 9d "bandes de messicoles"

Report (2006)

Post-invasion evolution of an invasive plant : altitudinal differenciation in germination and growth

Conference (2006)

Senecio inaequidens DC. was introduced from South Africa to Europe more than one hundred years ago, in a few precise locations linked to wool industry and extended its distribution throughout Europe. In a ... [more ▼]

Senecio inaequidens DC. was introduced from South Africa to Europe more than one hundred years ago, in a few precise locations linked to wool industry and extended its distribution throughout Europe. In a context of global warming, the potential evolution in germination and growth during the invasion process was studied in relation to altitude and climate. Seeds were collected along two transects (both altitudinal and climatic) in Belgium and France, going from the sea level to high altitudes (respectively 485 m and 1700 m) through the introduction spots. Respectively four and five climatic zones per transect, two populations per zone and ten randomly selected individuals per population were sampled. Seeds were sorted in order to discard maternal effects. Ten seeds per parent individual were thereafter sown in pots in a common garden experiment in Gembloux (Belgium). Germination was checked every two days. Height and diameter of plants, enabling the calculation of plant volume, were measured every 25 days. Despite an important variability, linear regression of first germination time (since sowing) vs altitude was significant (p = 0.001) for the French gradient, but not for the Belgian one. No significant difference was found in germination rate between climatic zones. For each of the three measurement times of plant height and diameter, regression of plant volume vs altitude was also significant for the French transect (p varying from 0.025 to 0.000 according to time), but not for the Belgian one. French plants from elevated locations germinated later and grow slowlier. These preliminary results suggest that contrasted climatic conditions in the French gradient, going from the Mediterranean coast to the Pyrrenean high elevations led to genetic differenciation of Senecio populations during its invasion in southern France. Less contrasted climatic conditions, together with a supposed loss of genetic variability (Lafuma 2003), did not lead to a clear differenciation in Belgium. References : Lafuma, L. (2003). L'invasion de Senecio inaequidens (Asteraceae) en Europe: une approche évolutive. PhD thesis, Montpellier University. [less ▲]

Evaluation des restaurations de pelouses calcicoles en Belgique en termes de structure spatiale et de diversité botanique

Conference (2006)

EVALUATION DES RESTAURATIONS DE PELOUSES CALCICOLES EN BELGIQUE : STRUCTURE SPATIALE, DIVERSITE BOTANIQUE ET CONDITIONS DE SOL

Conference (2006)

The role of heavy-metal stress on plant population genetic variation: the case of Viola calaminaria.

Conference (2005)

Evaluation des restaurations de pelouses calcicoles en région wallonne: coûts, structure écologique et diversité botanique

in Parcs & Réserves (2005), 60(4), 22-35

L’objectif de ce travail était de réaliser une première évaluation des actions de restauration de pelouses calcicoles effectuées dans les régions de Lesse et Lhomme et du Viroin (Belgique) depuis 15 ans ... [more ▼]

L’objectif de ce travail était de réaliser une première évaluation des actions de restauration de pelouses calcicoles effectuées dans les régions de Lesse et Lhomme et du Viroin (Belgique) depuis 15 ans. L’évaluation en terme de structure spatiale a montré que la surface totale de pelouses avait plus que doublé dans ces régions. Cette augmentation était surtout due à l’augmentation de la surface moyenne des pelouses et dans une moindre mesure à l’augmentation du nombre de pelouses présentes sur la zone. L’indice IFM de connectivité entre les pelouses a aussi augmenté. L’évaluation en termes de coûts a permis de montrer que le prix moyens des chantiers de restauration était d’environ 7000 €/ha. Ce prix augmentait avec la pente et la technique de restauration par gyrobroyage permettait de le diminuer là où elle était applicable. L’évolution de la flore suite à la restauration a ensuite été étudiée. Au cours du temps, la végétation sur les parcelles restaurées devenait plus nitrophobe, plus héliophile et contenait proportionnellement plus d’espèces typiques des pelouses, mais dans tous les cas, on n’atteignait pas le niveau des anciennes pelouses qui étaient aussi plus riches en espèces que les pelouses restaurées. L’influence de la nature du peuplement forestier présent avant restauration sur l’évolution de la flore est marquée au début, mais après un temps de 10 à 15 ans, plus aucune différence n’a été retrouvée. La recherche des espèces indicatrices a montré que les restaurations récentes étaient caractérisées par des espèces de coupes et forestières principalement alors que les restaurations anciennes et les pelouses témoins étaient indiquées majoritairement par des espèces de pelouses. Certaines espèces typiques des pelouses calcicoles ne sont pas réapparues sur les pelouses restaurées. [less ▲]