Stand structure and dendroecology of an old-growth Nothofagus forest in Conguillio National Park, south Chile

Abstract

The regeneration pattern and dynamics of two emergent southern beech trees ( Nothofagus alpina, Nothofagus dombeyi) were inferred from population age structure and spatial patterns in a forest dominated by the deciduous N. alpina in Conguillio National Park, south Chile. Diameter–frequency, diameter–age relations, and analysis of radial growth patterns of N. alpina (“raulı́”) and evergreen N. dombeyi (“coihue”) were examined at a montane elevation site in the Andean Range. The present age structure indicates that the oldest N. alpina established before 1463 and the oldest N. dombeyi between 1480 and 1520. The forest was uneven-aged as were the populations of raulı́ and coihue. N. alpina dominated the overstory layer, with few N. dombeyi dominant trees, and had fairly continuous recruitment between 1463 and 1984. Since 1885, tree recruitment in the forest has been dominated by both N. alpina and N. dombeyi. The master tree-ring chronology of N. alpina exhibited abrupt growth changes from 1650 to 1725. Increased growth rates occurred after a major volcanic explosion of Volcan Llaima around 1640, followed by a relatively sharp decline in growth from 1730 to 1850; growth remained high from the 1850s to the 1990s. Releases in radial growth, indicative of moderate- and small-scale disturbances occurred in most of the oldest trees during the last 400 years. Multiple periods of release and suppression indicate that N. alpina may take advantage of gaps to reach the main canopy. Gap turnover times in this N. alpina– N. dombeyi forest were estimated at >500 years, although gap formation was highly episodic and possibly associated with regionally strong windstorms, volcanic activity, and stand-level dieback. Gap and treefall characteristics in the forest are similar to results from other mixed Nothofagus forests in northern Patagonia, southern Chile and Tierra del Fuego. As the vegetation of the surveyed forest was homogenous over the last five centuries, it is concluded that regeneration and coexistence of long-lived Nothofagus spp. depends primarily on fine- and moderate-scale single treefall gaps.