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 (PC), 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 winterthan for spring-sown seedlings. In the xeric stand, emergence and survival of winter-sown seedlings increased with medium and high PC values, after the humid and dry summers, respectively. However, most spring-sown seedlings did not emerge, and those that did were shortlived. Because of the more favorable growing conditions in the mesic stand, PC 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 PC 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.

Effects of nurse shrubs and tree shelters on the survival and growth of two Austrocedrus chilensis seedling types in a forest restoration trial in semiarid Patagonia, Argentina

“…The above-average rainy conditions and moderate temperatures during the first growing season after planting may have somehow overcome, or masked, the protective effects given by either shrub cover or tree shelters. This effect is similar to what was reported in another study involving Austrocedrus seedlings, when above-average rainfall events prevailed during a specific growing season (Urretavizcaya et al 2012). However, these beneficial growth conditions found during the first season after plantation in this study drastically changed during the second growing season, when rains were 42 % lower and the mean temperatures 1.2°C higher than the long-term means.…”

“…The xeric sites of the Andean Patagonian ecotone present hot and dry summers (De Fina 1972), and these environmental conditions affect the emergence, survival, and growth of either naturally grown or planted Austrocedrus seedling. In these water-limited environments, Austrocedrus establishment may be enhanced by interactions between shrubs and Austrocedrus seedlings (Kitzberger et al 2000;Urretavizcaya et al 2012). During summer, nearby growing shrubs seem to protect Austrocedrus seedlings from direct radiation, and their shadow effect may improve the soil water availability around them (Kitzberger et al 2000).…”

“…During summer, nearby growing shrubs seem to protect Austrocedrus seedlings from direct radiation, and their shadow effect may improve the soil water availability around them (Kitzberger et al 2000). The effects of vegetation cover and density, coupled to the prevailing environmental conditions, likely affect Austrocedrus seed germination and early emergence (Urretavizcaya et al 2012). In these protected areas, this facilitation appears as an important factor for further Austrocedrus seedling establishment.…”

Experimental seed sowing reveals seedling recruitment vulnerability to unseasonal fire

“…2010, Urretavizcaya et al. 2012). The range of field emergence rates observed here were similar to previous seed‐sowing trials in the study region and elsewhere globally (Midgley et al.…”

¿Conviene seguir fomentando las plantaciones forestales en el norte de la Patagonia?

“…Desde la colonización europea y hasta poco tiempo atrás, la ganadería ovina (Defossé & Robberecht 1987) y la actividad forestal basada sobre el aprovechamiento del bosque nativo (Rothkugel 1916;Jovanovski et al 2003 (Urretavizcaya et al 2012;Quinteros 2014), a los incendios (Veblen et al 2008;Defossé et al 2014), a enfermedades como el mal del ciprés (Greslebin & Hansen 2010), al avance de la construcción en las áreas de interfaz urbano-rural (Defossé et al 2014) y a las medidas de protección. Hasta mediados de los años noventa del siglo pasado, la Patagonia Andina Central se autoabastecía y hasta exportaba madera de especies nativas.…”