Drought as an Inciting Mortality Factor in Scots Pine Stands of the Valais, Switzerland

Abstract

During the 20th century, high mortality rates of Scots pine (Pinus silvestris L.) have been observed over large areas in the Rhô ne valley (Valais, Switzerland) and in other dry valleys of the European Alps. In this study, we evaluated drought as a possible inciting factor of Scots pine decline in the Valais. Averaged tree-ring widths, standardized tree-ring series, and estimated annual mortality risks were related to a drought index. Correlations between drought indices and standardized tree-ring series from 11 sites showed a moderate association. Several drought years and drought periods could be detected since 1864 that coincided with decreased growth. Although single, extreme drought years had generally a short-term, reversible effect on tree growth, multi-year drought initiated prolonged growth decreases that increased a tree's long-term risk of death. Tree death occurred generally several years or even decades after the drought. In conclusion, drought has a limiting effect on tree growth and acts as a bottleneck event in triggering Scots pine decline in the Valais.

Response of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) to soil and atmospheric water deficits under Mediterranean mountain climate

“…In fact, Scots pine populations in the study area showed premature leaf loss during August 2003 and droughtinduced mortality occurred locally in other populations growing at lower elevations at the end of the spring of the year 2005 (personal observation). Besides, drought-induced mortality has been repeatedly observed in Scots pine stand from Mediterranean [28] and Central Europe populations [4]. On the contrary, Q. petraea was less affected than other coexisting species by the extreme 2003 summer drought in Central Europe [26].…”

Land-use and climate change effects in forest compositional trajectories in a dry Central-Alpine valley

“…The general trend from pine to oak can be divided into two processes: the mortality of Scots pine on the one hand and the spreading of broadleaves on the other hand. Several authors were able to relate pine mortality in the Valais directly to climate change -namely increased drought stress (Bigler et al, 2006;Rebetez and Dobbertin, 2004). Tree physiological studies show that Scots pine is more prone to drought effects than pubescent oak which is more resistant to extreme drought events (Poyatos et al, 2008;Weber et al, 2007;Zweifel et al, 2009).…”

“…However, mortality rates remained high or even increased in areas where fluorine loads has never been high and there is no evidence that other pollutants may be responsible for this effect (Rigling and Cherubini, 1999). Previous studies identified direct and indirect climate change effects namely increased drought stress (Bigler et al, 2006;Dobbertin et al, 2005;Rebetez and Dobbertin, 2004) and altered natural disturbance regimes (Gimmi et al, 2004;Schönfeld et al, 2004;Wermelinger et al, 2008;Zumbrunnen et al, 2009) as the main drivers of the shift in tree species composition. Because local-scale changes are not yet sufficiently understood, this study evaluates the role of historic anthropogenic disturbance regimes.…”

Faible différenciation génétique, à partir d'amplification aléatoire d'ADN polymorphe (RAPD), entre les types de pin sylvestre (Pinus sylvestrisL.) d'altitude et de plaine dans les Alpes à climat continental

“…Les premiers résultats de l'étude du dépérissement des pinèdes en Valais indiquent que l'affaiblissement des individus découle d'une association complexe de facteurs de stress comme la sécheresse [2,10], le gui (Viscum album ssp. austriacum) [11] et la concurrence [43,61] tandis que la mort résulte de l'action combinée de plusieurs agents pathogènes secondaires [43].…”