Aim This study investigates the role of fire and post fire succession in determining the structure and composition of vegetation on ultramafic iron crust soils.Location The study was conducted in the Plaines des Lacs region of southern New Caledonia.Methods A survey was made of eighty-eight sites, recording floristic composition, trunk size-class distributions, regeneration after fire, growth ring counts of Dacrydium araucarioides (Podocarpaccae) and historical information on past fires. Floristic data was ordinated using multidimensional scaling and an index of succession based on structural and historical information. A transition matrix model was developed to predict the effect of fire frequency on vegetation composition.Results The vegetation is undergoing postfire succession from maquis to forest, after about 75 years, and eventually to rainforest. Gymnostoma deplancheanum has a key role as an early colonist that produces shade, the bulk of the litter, and forms nitrogen fixing nodules with Frankia sp. However, the open canopy of Gymnostoma and slow litter decay creates flammable conditions. Though many species resprout from rootstocks, only thirty-nine persist through fires while 114 others colonize at later successional stages, as the litter layer and shade increase. Some early successional species are later excluded but these can persist locally in swamps and on rocky hill tops. Forest and rainforest are less flammable and the matrix model suggests that ignition frequency has a critical role in determining the abundance of maquis or forest.Main conclusions The vegetation mosaic represents a post fire succession from open maquis to forest. Palynological and charcoal records from late Pleistocene sediments suggest that fire has been a major factor determining the development of maquis vegetation since before the arrival of humans. Recently, frequent fires have converted much of the vegetation to maquis, posing a threat to some forest species and largely eliminating rainforest from iron crust soils. © 1999 Blackwell Science Ltd. Abstract reproduced by permission.