Replacement patterns and species coexistence in an Andean Araucaria-Nothofagus forest

Questions Fire appears to affect both replacement patterns and coexistence of Araucaria araucana-Nothofagus pumilio forests in the Andean Araucarian region of south-central Chile. A quantitative assessment of coexistence in the absence of recent fires, however, is lacking. In this study, we considered the life-history attributes, time of recruitment and spatial pattern of individuals of both tree species to address the following questions. How regular has recruitment of both species been in time? Is there any temporal niche differentiation? Are the two species positively or negatively associated in space and, if so, at what scale and for what age and size classes? Is there any spatial niche differentiation? Location Andean Araucarian region of Chile, Villarrica National Park (39 degrees 35'S, 71 degrees 31'W; 1300 m a.s.l.). Methods We stem-mapped and cored a total of 1073 trees in a 1-ha plot in a late-successional post-fire stand to examine spatiotemporal patterns of establishment. We used semivariogram modelling and the pair-correlation function to distinguish between regeneration modes and describe species interactions. Results The two species differ in their regeneration mode: whereas A. araucana appeared to recruit more continuously in time and space, episodic pulses of establishment were dominant for N. pumilio. At small scales, younger age-class stems of A. araucana were randomly distributed, while older age-class stems were aggregated. This was in contrast to common patterns for temperate tree species, including N. pumilio, following processes of self-thinning. Younger age classes of A. araucana were distributed independently of older trees of both species, but younger age classes of N. pumilio had a negative association with older conspecifics at scales similar to crown diameter. Conclusions In the absence of recent fires, it is likely that A. araucana would dominate the stand alone, given its greater shade tolerance, greater longevity and continuous recruitment. However, while canopy closure is still incomplete, the shade-intolerant N. pumilio will be able to recruit in those open areas after seed masting and will coexist with A. araucana.