Morphometric variation of leaves of Aphloia theiformis along an altitudinal gradient on La Réunion Island

The variation in length (L), width (l), shape index (L/l) and estimated area (2/3 L × l) of leaves of Aphloia theiformis (Flacourtiacées) has been analysed on a sample of 200 individuals along an altitudinal gradient on La Réunion Island (Mascarene archipelago). Leaf area and altitude are not correlated, but the former slightly decreases with the height of the vegetation (R = 0.254 ; P < 0.001). Leaf shape index decreases more acutely with the altitude (R = 0.579 ; P < 0.001). At this specifi c level, the altitude does not determine the variation of the leaf area, which remains partially linked with the vegetation structure. On the other hand, the altitude seems to determine more strongly the variation of the leaf shape inde

Modalities of colonization of woody savannah by dry forest plants in New Caledonia

Modalities of colonization of woody savannah by dry forest plants in New Caledonia. -Dry forests are the most endangered tropical forests in the world. Fortunately, they sometimes show some ability to colonize abandoned lands. Such a colonization potential has been investigated in the south of New Caledonia (Pacific Ocean). We analyzed the composition of the vegetation from transects from dry forest to proximate woody savannah, where an extension of the forest had been observed from the analysis of old aerial pictures. Three transects were followed in each of the four studied sites. Among 52 observed species, six were observed in more than 50% of the plots belonging to colonized sites. Among these six species, four provided suckers: Croton insularis, Elattostachys apetala, Emmenosperma pancherianum and Halfordia kendac. Ornithochory and barochory represented the dominant modes of seed dispersal of the colonizing species. Consequently, we conclude that fire control and bird conservation are relevant components of the conservation strategy of dry forest in New Caledonia.Dry forests are the most endangered tropical forests in the world. Fortunately, they sometimes show some ability to colonize abandoned lands. Such a colonization potential has been investigated in the south of New Caledonia (Pacifi c Ocean). We analyzed the composition of the vegetation from transects from dry forest to proximate woody savannah, where an extension of the forest had been observed from the analysis of old aerial pictures. Three transects were followed in each of the four studied sites. Among 52 observed species, six were observed in more than 50% of the plots belonging to colonized sites. Among these six species, four provided suckers: Croton insularis, Elattostachys apetala, Emmenosperma pancherianum and Halfordia kendac. Ornithochory and barochory represented the dominant modes of seed dispersal of the colonizing species. Consequently, we conclude that fire control and bird conservation are relevant components of the conservation strategy of dry forest in New Caledoni

Role of tree ferns in flowering plant settlement in the tropical montane rainforests of La Réunion (Mascarene Archipelago, Indian Ocean)

The mechanisms by which species richness of tropical forests is maintained are a source of ongoing debate. Indeed, even if variety of numerous microhabitats is a possible hypothesis, results remain inconclusive. In this study natural species regeneration on the soil was compared to that on tree fern stipes, a particular microhabitat type which is a safe place for the regeneration and maintain of flowering epiphytic plant species. Species that regenerate only underground or exclusively on tree fern stipes, or for some in these two microhabitat types, have been studied in this paper. The presence of numerous hemi-epiphytic indigenous species is highlighted and the specifi c regeneration on Cyathea spp. stipes is explained by specific life history traits (such as small seeds, seedling photo-sensibility, heliophilous saplings and anemochorous dissemination), which in particular give them the capability to hook on tree fern stipes and settle there. This “above ground” mode of growth should enhance the survival of heliophilous species particularly in invaded places by exotics plants. Tree ferns appear as playing an important role in the regeneration of a number of fl owering plants in Réunion tropical forests. In this 1-hectare study, 36.4 % of all regenerating flowering plants do it exclusively on tree fern stipes. A number of these species grow seedlings up to 80 cm on fern stipes, and then put down roots. This specific important hemi-epiphytic plant regeneration can in part explain the important species richness of tropical forests. Therefore, in order to preserve biodiversity, it is recommended to include tree ferns in future tropical forest restoration programsLes mécanismes expliquant la forte richesse spécifique des forêts tropicales suscitent de nombreux débats. En effet, même si l'importance des microhabitats est une hypothèse envisageable, les résultats à ce sujet restent flous. Dans cette étude, nous avons comparé la régénération naturelle des espèces indigènes et exotiques au sol et sur stipes de fougères arborescentes (Cyathea spp.), qui constituent un type de microhabitat particulier où la régénération et le développement des espèces épiphytes associées bénéficient d'un milieu favorable. Sont distinguées les espèces se régénérant exclusivement au sol, exclusivement sur stipe de Cyathea spp. ou dans ces deux types de microhabitats. La présence de nombreuses espèces indigènes hémi-épiphytes est soulignée et leur régénération unique sur Cyathea spp. justifiée par des traits d'histoire de vie (petites graines, dissémination anémochore, photosensibilité et héliophilie) leur conférant notamment une certaine capacité d'accrochage sur le stipe des fougères arborescentes. Ce mode de croissance 'hors sol' devrait favoriser la survie des espèces héliophiles en particulier au sein de milieux envahis par des plantes exotiques. Il est insisté sur le rôle important des fougères arborescentes dans la régénération d'une partie des plantes à fleurs de la forêt tropicale réunionnaise. Dans le cadre de cette étude, menée sur un hectare de forêt, 36,4 % des espèces indigènes qui se régénèrent le font exclusivement sur stipe de Cyathea spp. Une partie de ces espèces maintiennent des juvéniles sur les stipes jusqu'à ce qu'ils atteignent plus de 80 cm de hauteur et puissent s'enraciner au sol. Cette régénération abondante d'hémi-épiphytes permet d'expliquer en partie l'importante richesse spécifique des forêts tropicales. Il est donc recommandé d'intégrer les fougères arborescentes dans les futurs programmes de restauration écologique des forêts tropicales afin de préserver une large biodiversité

Can timber provision from Amazonian production forests be sustainable?

Around 30 Mm3 of sawlogs are extracted annually by selective logging of natural production forests in Amazonia, Earth's most extensive tropical forest. Decisions concerning the management of these production forests will be of major importance for Amazonian forests' fate. To date, no regional assessment of selective logging sustainability supports decision-making. Based on data from 3500 ha of forest inventory plots, our modelling results show that the average periodic harvests of 20 m3 ha−1 will not recover by the end of a standard 30 year cutting cycle. Timber recovery within a cutting cycle is enhanced by commercial acceptance of more species and with the adoption of longer cutting cycles and lower logging intensities. Recovery rates are faster in Western Amazonia than on the Guiana Shield. Our simulations suggest that regardless of cutting cycle duration and logging intensities, selectively logged forests are unlikely to meet timber demands over the long term as timber stocks are predicted to steadily decline. There is thus an urgent need to develop an integrated forest resource management policy that combines active management of production forests with the restoration of degraded and secondary forests for timber production. Without better management, reduced timber harvests and continued timber production declines are unavoidable

Defaunation changes leaf trait composition of recruit communities in tropical forests in French Guiana

Hunting impacts tropical vertebrate populations, causing declines of species that function as seed dispersers and predators, or that browse seedlings and saplings. Whether and how the resulting reductions in seed dispersal, seed predation, and browsing translate to changes in the tree composition is poorly understood. Here, we assess the effect of defaunation on the functional composition of communities of tree recruits in tropical rainforests in French Guiana. We selected eight sites along a gradient of defaunation, caused by differences in hunting pressure, in otherwise intact old-growth forests in French Guiana. We measured shifts in functional composition by comparing leaf and fruit traits and wood density between tree recruits (up to 5 cm diameter at breast height) and adults, and tested whether and how these compositional shifts related to defaunation. We found a positive relationship with defaunation for shifts in specific leaf area, a negative relationship for shifts of leaf toughness and wood density, and a weak relationship for shifts in fruit traits. Our results suggest that the loss of vertebrates affects ecological processes such as seed dispersal and browsing, of which browsing remains understudied. Even though these changes sometimes seem minor, together they result in major shifts in forest composition. These changes have long-term ramifications that may alter forest dynamics for generations