FIRE-INDUCED DYNAMICS OF ARAUCARIA ARAUCANA-NOTHOFAGUS-ANTARCTICA FOREST IN THE SOUTHERN ANDES

The emergent conifer Araucaria araucana (Mol.) K. Koch and the small deciduous broadleaved tree Nothofagus antarctica (Forst.) Oerst. occur as mixed post-fire stands in south-central Chile and Argentina. Both species are adapted to survive fire. Adaptations of A. araucana include thick bark, sprouting from epicormic buds and protected terminal buds on branches. N. antarctica resprouts vigorously after fire with multiple shoots. This study investigated the dynamics of this community, particularly in relation to fire. Recently burnt stands were examined for size-related response to fire. All A. araucana < 30 cm d.b.h. were killed with larger trees surviving. The size of these surviving A. araucana is probably related to fire intensity. Stand disturbance histories, population size and age distributions, diameter growth rate patterns and spatial relationships of different size classes, within and between species, were examined in intact stands. Most of these stands contained evidence of past fire. Within the first decade after fire, A. araucana (but not N. antarctica) seedlings or root suckers began to establish beneath the resprouted N. antarctica canopy. However, establishment was spatially clustered around surviving female A. araucana or abandoned caches of unknown seed predators. Once established, A. araucana grew through the sparse N. antarctica canopy, eventually overtopping it. This suppression of N. antarctica, if uninterrupted for more than 150 years, may lead to pure stands of A. araucana. However, fires are common in this region and both species possess attributes that promote accidental fires once ignited. Fire usually leads to formation of stands with clustered 10-20 m tall A. araucana over a 2-5 m tall N. antarctica subcanopy. Therefore, fire acts as a medium of species co-existence between a vigorously sprouting, shade-intolerant species (N. antarctica) and one that partly survives fire above-ground and is more shade-tolerant (A. araucana). The history of fire frequency and intensity on a site largely determine population structures for these species in mixed stands.