Effect of sowing season, plant cover, and climatic variability on seedling emergence and survival in burned Austrocedrus chilensis forests

Abstract

Fire is the most important disturbance factor in Cypress (Austrocedrus chilensis) forests in Patagonia, Argentina. This ecosystem recovers poorly after fire, and direct sowing could be a potentially useful restoration practice. To evaluate the effect of season of sowing, post-fire plant cover and climatic variability on seedling emergence and survival, three direct sowing studies were established in two burned cypress stands: Trevelin (xeric conditions) and El Bolsón (mesic conditions). Two studies were conducted in winter (2000 and 2001) and one in spring (2001). Precipitation was higher than the mean during the 2000-2001 growing season and lower during 2001-2002. At both sites, emergence and survival were much higher for winter-sown than for spring-sown seedlings. In the xeric stand, emergence and survival of winter-sown seedlings increased with medium and high plant cover values, after the humid and dry summers respectively; however, most spring-sown seedlings did not emerge, and those that did were short-lived. Because of the more favorable growing conditions in the mesic stand, plant cover had no effect on emergence and only favored first year survival of winter‑sown seedlings after the dry summer. Spring-sown seedlings showed no association with plant cover in the mesic site, probably because the first summer was exceptionally humid. We speculate that shading plants exert a positive effect on cypress seedling establishment, likely by reducing the stress from high temperatures and low water availability. Sowing of small patches under the protection of understory vegetation could be useful in restoring burned cypress stands.