Recruitment patterns following a severe drought: long-term compositional shifts in Patagonian forests

SUAREZ, MARIA LAURA; KITZBERGER, THOMAS

CANADIAN JOURNAL OF FOREST RESEARCH

NRC RESEARCH PRESS

Año: 2008 vol. 38 p. 3002 - 3010

0045-5067

Severe droughts have the potential of inducing transient shifts in forest canopy composition by altering speciesspecificadult tree mortality patterns. However, permanent vegetation change will occur only if tree recruitment patternsare also affected. Here, we analyze how a massive mortality event triggered by the 1998–1999 drought affected adult andsapling mortality and recruitment in a mixed Nothofagus dombeyi (Mirb.) Blume – Austrocedrus chilensis (D. Don) Flor.et Boult forests of northern Patagonia. Comparing drought-induced and tree-fall gaps, we assessed changes in forest composition,microenvironments, and seedling density and survival of both species. Drought-kill disturbance shifted speciescomposition of both canopy and sapling cohorts in favour of A. chilensis. Drought gaps were characterized by a shadierand more xeric environment, affecting the recruitment pattern of N. dombeyi seedlings. The seedling cohort was composedmostly of A. chilensis, and its survival was always higher than that of N. dombeyi. Additionally, A. chilensis seedlingsshowed higher plasticity than N. dombeyi seedlings, increasing its root to shoot ratios in drought gaps. The results suggestthat extreme drought itself is a strong driving force in forest dynamics, with important imprints on forest landscapes. Futureclimate-change scenarios, projecting an increased in frequency and severity of droughts, alert us about expected longtermcompositional shifts in many forest ecosystems.