Factors predisposing episodic drought‐induced tree mortality in Nothofagus– site, climatic sensitivity and growth trends

Abstract

Summary 1Although climatic variability is a strong driving force for forest dynamics, drought-induced mortality has generally received much less attention than other types of disturbance. 2 In 1998-99 northern Patagonia was affected by one of the most severe droughts of the 20th century, coinciding with a strong La Nina event, and this caused high mortality of Nothofagus dombeyi (coihue), the dominant tree species in Nahuel Huapi National Park. 3 Factors involved in determining this mortality of N. dombeyi were examined at both patch and tree level. Radial growth characteristics of killed trees and survivors were compared by dendrochronological analyses. Relationships between growth and climate were investigated using response function analysis. 4 At the tree scale, individuals with variable growth were more prone to die from drought than trees with more regular growth. Juveniles whose growth patterns showed sensitivity to climate were particularly likely to die. However, among both killed trees and survivors, older trees were less sensitive to climate. 5 Mean growth rate was a good predictor of mortality in adult trees, showing that trees with slower growth rate were more susceptible to drought. Susceptible trees may have been negatively affected by the drought that affected northern Patagonia in 1956-57. 6 These results underscore the importance of considering drought-induced tree mortality as a non-random mechanism influenced by site, previous stress/disturbance history, ontogeny, vigour, climatic sensitivity and physiology. Spatial patterns of extensive full and partial crown dieback, which are evident in many temperate forests worldwide, may reflect the superposition of these predisposing factors on strong / repeated interannual fluctuations of climate.

The effects of thinning intensity and tree size on the growth response to annual climate in Cedrus atlantica: a linear mixed modeling approach

“…The interpretation of this higher sensitivity from the viewpoint of the ability of cedar to cope with drought effects is not straightforward, and we still lack a conceptual framework linking the growth signal features to life traits (Cuny et al 2012) and demography (Martínez-Vilalta et al 2012). Indeed, previous studies produced seemingly contradictory results, reporting higher mortality rates for trees showing highly variable growth (Suarez and Ghermandi 2004) or a weaker correlation between the growth of the dying trees and the climate variables (Linares et al 2010). As recent reports suggest a lower capacity of large trees to overcome severe drought (Bigler and Veblen 2009), the long-term effect on thinning on the ability of mature cedar stands to survive extreme water stress events need further investigations.…”

Temperate forest trees and stands under severe drought: a review of ecophysiological responses, adaptation processes and long-term consequences

“…Some additional stress factors like soil hydromorphy or nitrogen excess could also be involved in the process. A growing body of evidence in the literature supports the notion that the risk of tree death increases with a decreasing growth rate [107,140]. Wyckoff and Clark [155], using various growth-mortality functions, showed that dead trees of Cornus florida and Acer rubrum exhibited lower growth rates during the 5 years prior to mortality than surviving ones.…”

Using longitudinal survival probabilities to test field vigour estimates in sugar maple (Acer saccharum Marsh.)

“…This variable represents the responsiveness of individuals to environmental signals, such as climate (Fritts, 1976). High sensitivity values have been associated with tree vigour decline because dying trees may exhibit higher variability in past growth rates (Ogle et al, 2000;Suarez et al, 2004). Interannual sensitivity was defined as (Fritts, 1976):…”