Stéphane Baret

An Assessment of Habitat Diversity and Transformation on La Réunion Island (Mascarene Islands, Indian Ocean) as a Basis for Identifying Broad-scale Conservation Priorities

Most natural habitat in the Mascarene Islands (Mauritius, La Réunion and Rodrigues) has been transformed. Although urbanisation, agriculture and alien plant invasions have transformed large areas in La Réunion, the island has by far the greatest area of intact habitats in the Mascarenes, but remaining natural areas are under threat. We propose a protocol for defining a system of habitat types and for using these to provide a preliminary assessment of conservation priorities for La Réunion. The protocol draws on existing data and expert knowledge to map habitat types, assesses the extent of habitat transformation, and quantifies heterogeneity between habitat types based on climate, topography and geology. The pattern of habitat transformation was uneven among the nineteen habitat types identified. While three habitats have lost > 95% of their original area, four still retain> 80% of their original extent. Habitat types could be grouped into the following categories: (i) transformed habitats with low levels of plant endemism, (ii) habitats confined to homogenous geology with high levels of plantendemism, and (iii) species-rich heterogeneous habitats on diverse geological types. Priority habitats were also identified using municipalities as a basis for implementation. Urgent action is required for several habitat types where a large part of the original extent has been transformed. Three municipalities which contain more than 10 habitat types should receive conservation priority. The analysis provides the basis for setting conservation priorities in La Réunion at the regional and local scale. Implications of the results are discussed with reference to requirements for finer-scale conservation planning.

Altitudinal variation in fertility and vegetative growth in the invasive plant Rubus alceifolius Poiret (Rosaceae), on Réunion island.

Rubus alceifolius Poiret (Rosaceae) was introduced to the island of Réunion in the southeastern Indian Ocean about 1850 and is now highly invasive. This bramble, native from southeastern Asia and Malaysia, has invaded a wide variety of habitats (lowland rainforest, mountain and submountain rainforest, Acacia heterophylla rainforest) from sea level to 1700 m. It is suspected to be monoclonal so, its remarkable success may be due in part to great phenotypic plasticity. On Réunion, bud, flower, fruit and seed production, the duration of the flowering period and the importance of the seed bank were found to be negatively correlated with elevation (50-1500 m a.s.l.). At a lowland site, fruit production in mature stands averaged between 30 and 80 fruits/m2 during 1999 and 2000. No fruit set occurred above 1100 m. This fruit production pattern was similar over two years. Although the number of leaves per unit area is similar along the whole gradient studied, decrease of fruit set in upland areas might be compensated for by an increase in vegetative growth. Temperature variation is very sharp along the elevation gradient and may control the fruit and the seed production. Fruit production allows establishment of new populations all around the island via bird dissemination. Once established, R. alceifolius maintains dense patches that can grow vegetatively. Our results may be relevant for eradication programs that should take into account variation in reproductive strategy in lowland vs. highland habitats.

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 Reunion affected the invasiveness of alien plants. In the 12 000-m 2 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 m 2 ). 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 invasive.

Threats to Paradise? Plant Invasions in Protected Areas of the Western Indian Ocean Islands

The islands of the Western Indian Ocean are well known for their unique biodiversity. However, much of the native habitat has been destroyed and the remainder is threatened by invasive alien species. In this review we assessed the different protected area systems, synthesised the history of invasive alien plants and actions against them, and compared contrasting approaches in habitat management across the different island groups. Of the total terrestrial area of the Western Indian Ocean Islands, a third is under formal protection (defined as all six IUCN categories of protected areas), with the proportion of protected areas and conservation status differing substantially between the islands. The awareness of the problems related to protected areas and specific invasive alien plant control actions, and which are supported by official government strategic documents, are further developed in Mauritius-Rodrigues, La Reunion, and Seychelles, but are still to be developed for the Comoros archipelago. We discuss the different approaches to management across the islands, the varying habitat types, fragmentation and degree of invasion. Invaded habitats are being managed by a range of approaches, including restoration, re-creation or inclusion as a novel ecosystem. We conclude by suggesting improvements in the protected area system in the Western Indian Ocean Islands, including priority actions that are necessary to prevent further invasion and control of invasive alien species already in the region.

Opportunities for classical biological control of weeds in european overseas territories

Summary European overseas territories are home to biodiversity and endemism of worldwide importance, vastly superior to that of continental Europe as a whole. They are, however, much more threatened by invasive species, including hundreds of alien invasive plant species having a huge impact on natural and agricultural habitats. As in continental Europe, invasive plants have only recently been recognized as a threat to the local environment and biodiversity. Mechanical and chemical control programmes—underway for several decades—have not been entirely successful for permanent, costeffective, environment-friendly management. Biological control of weeds has long been successfully used in other neighbouring countries with similar climates, environmental conditions and invasions, but has barely been implemented in European overseas territories. There have been very few attempts to set up classical biological control programmes in these regions—a few of the species that have been the focus of biological control are Lantana camara L., Rubus alceifolius Poir., Opuntia stricta (Haw.) Haw., Acanthocereus tetragonus (L.) Britton & Rose, Ligustrum robustum (Roxb.) Blume, Miconia calvescens DC., Ulex europaeus L., Prosopis juliflora (SW.) DC., and Leucaena leucocephala (Lam.) de Wit. Many invasive plants occurring in European overseas territories are also invasive elsewhere and already targets of biological control programmes. Biological control agent specificity requires particular attention due to the high level of endemism in such islands. This paper reviews some of the most threatening species for which classical biological control could be achieved through regional or international collaboration.