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

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 km 2 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 animaldispersed trees as well as a decrease in the abundance of large trees with increasing proximity to forest edges. Near forest edgeswe 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.