Can species richness be maintained in logged endemic Acacia Heterophylla forests (Reunion Island, Indian Ocean) ?

It is assumed that forests can serve multiple uses, including wood production and maintenance of high biodiversity level. We tested this hypothesis by studying eradication methods of invasive plants currently implemented in exploited endemic Acacia heterophylla forests located in a tropical highland forest region on the island of Réunion. We also compared species richness in logged (over time) and natural forests. Our results show that all individuals of the widespread alien invasive plant Rubus alceifolius were generated from cuttings. We quantifi ed the high growth capability of this species by comparing with those of Acacia heterophylla along with Rubus apetalus var. apetalus, a close non-invasive congener. The substantial multiplicative and vegetative growth ability of R. alceifolius enabled it to form monospecific patches in only 2.5 years. The species richness of the exploited Acacia heterophylla forest was thus very affected. Although the species richness increased over time after logging, the extent of the resulting richness was not as great as that in natural forests which, moreover, included numerous exotic plants. The authors assess the impact of highly disturbing logging operations and, based on the results of the comparisons, are very pessimistic about the possibility of maintaining species richness in logged forests. Nevertheless, the results indicate that the situation is not beyond hope and an eradication program specifi cally tailored to this kind of forest is proposed if exploitation will stop

Identification d'une nouvelle proie du Busard de Maillard (Circus maillardi) : observation d'une capture de poisson au niveau du site de Grand-Étang sur l'île de La Réunion (Accipitriformes : Accipritidae)

Le Busard de Maillard ou Papangue, est la seule espèce nicheuse de rapace de l'île de La Réunion, dont il est endémique. Il est classé en danger d'extinction par l'IUCN. De ce fait de nombreuses actions de connaissances sont encore nécessaires afin de mettre en œuvre et au mieux les actions de conservation. Dans ce cadre, toutes informations complémentaires sur la biologie et l'écologie de cette espèce s'avèrent importantes. L'observation faite ici est donc intéressante puisqu'elle permet de confirmer que les poissons, préférentiellement de couleurs vives, font partie du régime alimentaire de ce rapace. Il sera donc important de tenir compte de cette nouvelle information, pour les sites potentiels de colonisation de l'espèce, mais aussi pour les risques d'impact sur l'oiseau dont les nouvelles sources d’empoisonnement, notamment si les rivières sont polluées

Les effets de l’ouverture de sentiers sur l’invasion des zones protégées de l’île de la Réunion (archipel des Mascareignes, océan Indien) par des espèces végétales exotiques.

Les effets de l'ouverture de sentiers sur l'invasion des zones protégées de l'île de la Réunion (archipel des Mascareignes, océan Indien) par des espèces végétales exotiques. - L'envahissement par les espèces exotiques est devenu un problème majeur au niveau des aires protégées. Une meilleure connaissance de leur impact sur le fonctionnement des écosystèmes est nécessaire pour améliorer les pratiques de gestion et la conservation des habitats. Nous suggérons que les effets des perturbations comme l'ouverture de chemins forestiers et l'invasion par les plantes exotiques sont sous-estimés. Nous avons donc quantitativement mesuré le rôle de l'ouverture de chemins forestiers dans la colonisation par les plantes envahissantes, un phénomène en progression constante mais jamais étudié auparavant. Notre étude montre que Rubus alceifolius, la plante exotique envahissante la plus répandue à La Réunion, est capable de germer aussi bien au niveau d'un chemin étroit que d'un chemin large mais ne persiste qu'au niveau du chemin le plus large. Nos résultats montrent aussi qu'un chemin large favorise l'établissement des plantes exotiques et détermine une réduction significative de la richesse spécifique. Cette étude conduit à suggérer aux forestiers de construire plutôt des chemins étroits, ce qui permettrait d'empêcher l'installation et la propagation de R. alceifolius et des autres plantes non indigènes.Exotic species have become a major problem in protected areas. A better knowledge of ecosystem functioning is necessary to improve management practice that facilitates habitat conservation. We suggest that small-scale disturbances such as trail opening and the effects on exotic plants invasions are underestimated. We have, therefore, quantitatively measured the effect of forest trail building on invasive plant colonization, a phenomenon in constant progression but never studied before. Our study shows that Rubus alceifolius, the widespread exotic invasive plant on La Réunion, is able to germinate on both narrow and wide trails, but persists only on the wider ones. Our results show moreover that wide forest trails favored establishment of exotics and significantly decreases species richness. We suggest to forest managers that building narrow forest trails is preferable as it will stop the persistence and propagation of R. alceifolius and other non-indigenous plants

An extremal model for amorphous media plasticity

An extremal model for the plasticity of amorphous materials is studied in a simple two-dimensional anti-plane geometry. The steady-state is analyzed through numerical simulations. Long-range spatial and temporal correlations in local slip events are shown to develop, leading to non-trivial and highly anisotropic scaling laws. In particular, the plastic strain is shown to statistically concentrate over a region which tends to align perpendicular to the displacement gradient. By construction, the model can be seen as giving rise to a depinning transition, the threshold of which (i.e. the macroscopic yield stress) also reveal scaling properties reflecting the localization of the activity.Comment: 4 pages, 5 figure

Effects of canopy gap size on recruitment and invasion of the non-indigenous Rubus alceifolius in lowland tropical rain forest on Réunion

An important challenge of invasion biology is to understand how interactions between species traits and ecosystem properties enable alien species to become invasive at particular locations. We investigated how gap dynamics in a tropical rain forest on the island of Réunion affected the invasiveness of alien plants. In the 12 000-m2 study area, alien plants occupied 24.9% of the area of gaps, which represented 5.62% of the forest area, but only 0.8% of the understorey area. The most abundant invasive species was Rubus alceifolius, which formed dense, monospecific stands in the largest gaps (> 25 m2). Although plants could persist in the shade, a germination experiment revealed that canopy openings were essential for seedling establishment. A cyclone that struck the study area in 2002 caused a temporary thinning of the canopy, increasing light levels to above the threshold needed for germination of R. alceifolius and also stimulating the growth of established plants. We conclude that the ability of this and other alien species to colonize intact lowland tropical rain forest is strongly influenced by the prevailing gap dynamics. Because gaps are also essential for the regeneration of many native trees in our study area, there is a real danger of the forest being progressively degraded by alien plants. There are no simple solutions to controlling species such as Rubus alceifolius, but efforts should be focused mainly upon the larger gaps where the species are most invasiv