Early performance of planted Nothofagus dombeyi and Nothofagus alpina in response to light availability and gap size in a high-graded forest in the south-central Andes of Chile

The Andes of south-central Chile (38 - 41 degrees S) were once dominated by highly productive and valuable forests mainly dominated by Nothofagus dombeyi and N. alpina, but their exploitation led to extensive areas at present covered by high-graded stands. Although these tree species exhibit a light-demanding character and naturally grow in regions with severe winters, they show high mortality when planted in open areas with frequent spring frosts. The effect of light intensity and gap size on survival, size and form of N. dombeyi and N. alpina seedlings, planted in a high-graded stand, was analyzed. Direct and diffuse light (measured through hemispheric photographs) and effective gap area (range from 40 to 734 m(2)) were estimated in 23 forest gaps, which were divided into small, medium and large for each species (12 gaps for N. dombeyi and 11 gaps for N. alpina). After two growing seasons, mean survival of N. dombeyi was > 95% and not significantly different among gap categories; in N. alpina there was complete survival in medium-sized gaps, which was significantly different from survival in the larger and smaller gaps. Growth of Nothofagus dombeyi significantly increased with gap size and light availability; a phenomenon which did not occur in N. alpina. Nothofagus alpina experienced a lower slenderness within larger gaps. This study suggests that rehabilitation of high-graded stands, based on plantations of genus Nothofagus, is an ecologically viable option although control of canopy and understory covers is required.