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

Mode de colonisation de la savane arborée par des plantes de forêt tropicale sèche en Nouvelle-Calédonie

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.Bocquet Aurélie, Chambrey Céline, Derroire Géraldine, Tassin Jacques. Mode de colonisation de la savane arborée par des plantes de forêt tropicale sèche en Nouvelle-Calédonie. In: Revue d'Écologie (La Terre et La Vie), tome 62, n°1, 2007. pp. 87-91

How does forest fragmentation affect tree communities? A critical case study in the biodiversity hotspot of New Caledonia

International audienceContext: The biodiversity hotspot for conservation of New Caledonia has facing high levels of forest fragmentation. Remnant forests are critical for biodiversity conservation and can help in understanding how does forest fragmentation affect tree communities.Objective: Determine the effect of habitat configuration and availability on tree communities.Methods: We mapped forest in a 60 km2 landscape and sampled 93 tree communities in 52 forest fragments following stratified random sampling. At each sampling point, we inventoried all trees with a diameter at breast height ≥10 cm within a radius of 10 m. We then analysed the response of the composition, the structure and the richness of tree communities to the fragment size and isolation, distance from the edge, as well as the topographical position.Results: Our results showed that the distance from the forest edge was the variable that explained the greatest observed variance in tree assemblages. We observed a decrease in the abundance and richness of animal-dispersed trees as well as a decrease in the abundance of large trees with increasing proximity to forest edges. Near forest edges we found a shift in species composition with a dominance of stress-tolerant pioneer species.Conclusions: Edge-effects are likely to be the main processes that affect remnant forest tree communities after about a century of forest fragmentation. It results in retrogressive successions at the edges leading to a dominance of stress-tolerant species. The vegetation surrounding fragments should be protected to promote the long process of forest extension and subsequently reduce edge-effects

Les forêts humides de la province Nord, Nouvelle-Calédonie : synthèse des travaux de recherche 2012-2015

International audienceEt si l'or vert de la Nouvelle-Calédonie n'était pas les roches nickélifères enfouies dans son sous-sol mais plutôt ses forêts luxuriantes qui habillent la Chaîne Centrale ? Installées depuis des millions d'années, que sait-on aujourd'hui de ces forêts ? Comment fonctionnent-elles ? Comment sont-elles organisées ? Comment se régénèrent-elles ? Et surtout, d'où vient leur originalité écologique et floristique ? Depuis 2012, la province Nord s'est engagée dans un partenariat pluriannuel avec l'équipe de recherche en écologie forestière de l'Institut Agronomique néo-Calédonien (IAC) pour mieux connaître ce patrimoine naturel et culturel aussi riche que vulnérable. Leur objectif commun : améliorer les connaissances sur les forêts denses humides de la province Nord afin d'optimiser leur gestion et leur préservation par les services du Développement Economique et de l'Environnement (DDEE). Pendant près de quatre ans, depuis le sol, les airs et même depuis l'espace, les scientifiques ont observé, inventorié, mesuré, décrit, analysé les forêts humides de la province Nord. Désormais, ils en savent davantage sur leur distribution géographique, composition, organisation, dynamique et leur fragilité. Ce travail de grande ampleur résulte d'une collaboration scientifique entre l'IAC, le Cirad, l'IRD, l'unité mixte de recherche AMAP, et le CNES, avec le soutien financier de la Province Nord. Cet ouvrage collectif propose une synthèse illustrée des connaissances acquises lors de cet ambitieux programme de recherche et vous invite à découvrir les étonnants secrets des forêts humides néo-calédoniennes, qu'il devient urgent de préserver

Prédire la structure des forêts tropicales humides calédoniennes : analyse texturale de la canopée sur des images pléiades

National audienceLarge-scale characterization of tropical rainforest is a challenge for their conservation and management. Very high spatial resolution images as provided by the Pléiades satellites offer new opportunities to study the structural organization of heterogeneous rainforests with limited accessibility. In this study, we have evaluated the potential of Pléiades images to map structural parameters of New Caledonian rainforests by analyzing texture of forest canopies. We have applied the Fourier transform textural ordination (FOTO) method to very high spatial resolution images to compute texture indices of canopy grain (i.e. a combination of size distribution and spatial pattern of tree crowns). The results have showed that this method was promising to isolate the rainforest from other types of vegetation, and to highlight their structural diversity on a large scale. Finally, this case study showed that the use of Pléiades images is promising to predict the structure of rainforests.Cartographier et classifier les forêts denses humides (FDH) selon une typologie structurale objective est un enjeu majeur pour leur conservation et leur gestion. Les principales contraintes dans l'étude des FDH sont dues à leur forte hétérogénéité et à leur faible accessibilité. Les images satellitaires Pléiades offrent de nouvelles opportunités pour l'étude, à large échelle, de l'organisation structurale de ces forêts. Dans cet article nous avons évalué à travers une étude de cas en Nouvelle-Calédonie leur potentiel pour construire une typologie des FDH à partir d'une analyse de texture de la canopée. La méthode FOTO (FOurier-based Textural Ordination) a été appliquée à des images à très haute résolution spatiale pour produire des indices de texture du grain de la canopée, qui associent la distribution des tailles des couronnes des arbres et leur répartition spatiale. Les résultats ont montré que cette méthode permettait, d'une part d'isoler la FDH des autres formations végétales, et d'autre part de mettre en évidence leur diversité structurale à large échelle. Enfin, cette étude de cas a montré que l'utilisation d'images Pléiades est prometteuse pour prédire la structure des forêts denses humides. Mots-clés : Structure de la canopée, analyse de texture, forêt dense humide, Nouvelle-Calédonie, télédétection, image à très haute résolution Abstract Large-scale characterization of tropical rainforest is a challenge for their conservation and management. Very high spatial resolution images as provided by the Pléiades satellites offer new opportunities to study the structural organization of heterogeneous rainforests with limited accessibility. In this study, we have evaluated the potential of Pléiades images to map structural parameters of New Caledonian rainforests by analyzing texture of forest canopies. We have applied the Fourier transform textural ordination (FOTO) method to very high spatial resolution images to compute texture indices of canopy grain (i.e. a combination of size distribution and spatial pattern of tree crowns). The results have showed that this method was promising to isolate the rainforest from other types of vegetation, and to highlight their structural diversity on a large scale. Finally, this case study showed that the use of Pléiades images is promising to predict the structure of rainforests

Caractérisation des connectivités structurelle et fonctionnelle des paysages fragmentés sur sols ultramafiques

- L'objectif principal du programme « Corifor, corridors entre îlots forestiers » était de déterminer dans quelle mesure la fragmentation actuelle des paysages agit sur les relations liant la composition (floristique et biologique) des peuplements forestiers avec la structure (superficie et distance inter-isolat) d'un environnement forestier fragmenté.- Les résultats apportent des éléments de compréhension sur l’évolution des paysages fragmentés du Grand Sud calédonien et des recommandations pour la restauration en vue de la création de corridors écologiques opérationnels, notamment dans un contexte minier.- La définition de la classe « forêt dense humide » au sens réglementaire est discutée, dans l’objectif de renforcer les mesures de protection des forêts.- Enfin sont suggérées 6 règles majeures qu’il conviendrait de suivre pour améliorer la gestion des forêts du Grand Sud calédonien