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

The emergent conifer Araucaria araucana (Mol.) K. Koch and the small d eciduous broadleaved tree Nothofagus antarctica (Forst.) Oerst. occur as mixed post-fire stands in south-central Chile and Argentina. Both s pecies 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 multi ple shoots. This study investigated the dynamics of this community, pa rticularly in relation to fire. Recently burnt stands were examined fo r size-related response to fire. All A. araucana < 30 cm d.b.h. were k illed with larger trees surviving. The size of these surviving A. arau cana is probably related to fire intensity. Stand disturbance historie s, population size and age distributions, diameter growth rate pattern s and spatial relationships of different size classes, within and betw een species, were examined in intact stands. Most of these stands cont ained evidence of past fire. Within the first decade after fire, A. ar aucana (but not N. antarctica) seedlings or root suckers began to esta blish beneath the resprouted N. antarctica canopy. However, establishm ent was spatially clustered around surviving female A. araucana or aba ndoned 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 sta nds with clustered 10-20 m tall A. araucana over a 2-5 m tall N. antar ctica subcanopy. Therefore, fire acts as a medium of species co-existe nce between a vigorously sprouting, shade-intolerant species (N. antar ctica) and one that partly survives fire above-ground and is more shad e-tolerant (A. araucana). The history of fire frequency and intensity on a site largely determine population structures for these species in mixed stands.