Limitantes físicos y bióticos de la regeneración arbórea en matorrales sucesionales de la Isla Grande de Chiloé, Chile

Abstract

Successional shrublands created by clearcutting and burning of forests are frequent in Chiloe Island and surrounding mainland in southern Chile. These areas are characterized by seasonally waterlogged soils, and vegetation dominated by sedges, ferns and shrubs, such as Baccharis patagonica, with thick carpets of Sphagnum moss occupying the spaces between shrubs. Tree regeneration in these sites was shown to be sparse or completely lacking (< 0.3 seedlings m(-2)) compared with 7.2 seedlings m(-2) in adjacent forests. Colonization of shade-intolerant, pioneer trees may be reduced underneath Baccharis due to crown shading and on top of Sphagnum cushions, because of unfavorable conditions for tree establishment, including low pH and soil water saturation. We evaluated differences in germination rates among pioneer tree species grown in an experimental soil moisture gradient. Seed germination percentage was low for Drimys winteri and Nothofagus nitida unrelated to humidity conditions but differed between substrates (moss vs. soil). Embothrium had higher germination and survivorship when growing on Sphagnum cushions. We also monitored seedling survival of two pioneer tree species (Embothrium coccineum and Drimys winteri) transplanted directly under Baccharis shrubs, in open areas, or on moss patches. Even though survivorship of Embothrium and Drimys under Baccharis was < 40%, in one of the study sites, there were no differences between treatments. Waterlogged soils would constraint tree regeneration on successional shrublands due to a lack of elevated substrates. However, the presence of Sphagnum cushions favors Embothrium establishment, and thus may facilitate restoration of these sites.