Context: 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. (Résumé d'auteur
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.
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