Austral Ecology (2005) 30, 363–373 Accepted for publication June 2004. Disturbance processes and spatial patterns of two emergent conifers in New Caledonia LESLEY S. RIGG Department of Geography, Northern Illinois University, DeKalb, Illinois 60115, USA (Email: lrigg@niu.edu) Abstract Araucaria laubenfelsii Corbasson and Araucaria montana Brongn et Gris are emergent conifers in maquis and forest communities which are subjected to a combination of fire and cyclonic disturbances. Both species are able to survive fire once stems reach a critical size, but most seedlings and saplings are killed. Both species were found to be clumped at most spatial scales for both saplings and trees in maquis, probably resulting from a combination of patchy fire and a limited ability to disperse seeds. Comparisons of burned and unburned A. montana sites suggest that clumping increases only slightly after fire. The degree of clumping in the A. laubenfelsii sites, suggested that fire disturbances may occur relatively frequently in the region. Cyclonic disturbances are infrequent but may result in blow-down of large individuals within both maquis and forest. All of the individuals blown-down during the study had been previously fire-scarred. Around tree blow-downs, seedling and sapling densities can be high. This likely reflects both the low dispersability of Araucaria seeds and enhanced moisture from the shading of the adult, when it was alive. Disturbance by fire and wind play an important role in the regeneration dynamics and spatial pattern of these species in maquis in New Caledonia. Key words: Araucaria, cyclone, disturbance, fire, spatial analysis INTRODUCTION Most studies of long-lived tree species are conducted over a brief period of time relative to the lifetime of the tree. Therefore, demographic processes must be inferred from the past and present characteristics of the species’ population (Veblen 1992). The spatial distribution of adult trees results from the various demographic and physical processes that have been operating over the life-time of trees and may also reflect responses to disturbance (Hatton 1989; Rebertus et al. 1989; Haase 1995). Many studies have examined spatial pattern and the pattern scale within plant communities in an attempt to determine the underlying controlling factors (Stewart & Rose 1990; Burns 1991; Gibson & Brown 1991; Couteron & Kokou 1997; Wells & Getis, 1999). In forest communities, gap-phase regeneration can result in an intermediate degree of clumping as the distribution of stems reflects the spatial distribution of previous tree-fall gaps (Lusk & Ogden 1992). Over time, patterning in forest communities may progress from clumped to random to regular (Rebertus et al. 1989; Lusk & Ogden 1992; Wells & Getis 1999). Clumping may become less intense with time as a result of self-thinning (Veblen & Stewart 1980; Sterner et al. 1986; Veblen 1992). When a tree species is regen- erating continuously within a community and not rely- ing on canopy gaps, the spatial distribution of stems would be highly clumped if the species reproduces vegetatively or has poorly dispersed seeds (Veblen & Stewart 1980; Sterner et al. 1986). A random distri- bution of stems might be expected when a species has very effective seed dispersal, is growing on an environ- mentally homogenous site, or is very tolerant of envi- ronmental heterogeneity (Rebertus et al. 1989; Barot et al. 1999). In communities lacking an intact tree canopy, such as heathlands, gap-phase regeneration does not occur, rather species are more likely to undergo continuous regeneration following episodic wildfire. Worldwide, the age, structure and species composi- tion of many maquis/heathland communities are determined by fire frequency and intensity (Trabaud 1994). Post-fire regeneration responses of maquis/ heathland species and resulting vegetation patterns have been studied extensively in the Mediterranean region (Trabaud & Lepart 1980; Gratani & Amadori 1991; Paraskevopoulos et al. 1994; Clemente et al. 1996; Ojeda et al. 1996), South Africa (Bond et al. 1984), California (Christensen & Muller 1975; Keeley et al. 1981) and Australia (Specht 1981; Enright & Lamont 1989; Hobbs & Atkins 1990; Hodgkinson 1991; Enright & Goldblum 1999). Disturbances, such as fire and in certain regions blow-down (e.g. North- ern Australia), affect the spatial organization of these communities. Fire patchiness can result in varying patterns of death among trees and saplings. For exam- ple, Rebertus et al. (1989) found the distribution of