Factors predisposing episodic drought-induced tree mortality in Nothofagus - site, climatic sensitivity and growht trends

SUAREZ, MARIA LAURA; GHERMANDI, LUCIANA; KITZBERGER, THOMAS

JOURNAL OF ECOLOGY (PRINT)

British Ecological Society

Año: 2004 vol. 92 p. 954 - 966

0022-0477

1Although climatic variability is a strong driving force for forest dynamics, drought-inducedmortality has generally received much less attention than other types of disturbance.2In 1998–99 northern Patagonia was affected by one of the most severe droughts of the20th century, coinciding with a strong La Nina event, and this caused high mortality ofNothofagus dombeyi(coihue), the dominant tree species in Nahuel Huapi National Park.3Factors involved in determining this mortality ofN. dombeyiwere examined at bothpatch and tree level. Radial growth characteristics of killed trees and survivors werecompared by dendrochronological analyses. Relationships between growth and climatewere investigated using response function analysis.4At the tree scale, individuals with variable growth were more prone to die fromdrought than trees with more regular growth. Juveniles whose growth patterns showedsensitivity to climate were particularly likely to die. However, among both killed treesand survivors, older trees were less sensitive to climate.5Mean growth rate was a good predictor of mortality in adult trees, showing that treeswith slower growth rate were more susceptible to drought. Susceptible trees may havebeen negatively affected by the drought that affected northern Patagonia in 1956–57.6These results underscore the importance of considering drought-induced treemortality as a non-random mechanism influenced by site, previous stress/disturbancehistory, ontogeny, vigour, climatic sensitivity and physiology. Spatial patterns of extensivefull and partial crown dieback, which are evident in many temperate forests worldwide,may reflect the superposition of these predisposing factors on strong/ repeated interannualfluctuations of climate.