© 2004 Heron Publishing—Victoria, Canada
Influence of climate on radial growth of Pinus cembra within the alpine timberline ecotone
Walter Oberhuber
Institut für Botanik, Universität Innsbruck, Sternwartestrasse 15, A-6020 Innsbruck, Austria (Walter.Oberhuber@uibk.ac.at) / Received March 19, 2003; accepted September 13, 2003; published online January 2, 2004
Summary
Radial growth variability and response to interannual climate variation of Cembran pine (Pinus cembra L.) were studied in the timberline ecotone on Mt. Patscherkofel (2246 m a.s.l.). The study area, which is in the inner alpine
dry region of the Central Austrian Alps, is characterized by a continental climate with minimum precipitation in winter (about
150 mm during December–February) and frequent occurrence of warm dry winds (Föhn) in early spring. The hypothesis that spatial
and temporal variability of radial growth is caused by site-related differences in sensitivity to winter stress (i.e., desiccation)
was examined by applying dendroclimatological techniques. Ordination methods applied to tree ring time series revealed that
spatial variability in radial growth is influenced by the local site factors elevation and slope aspect. Growth–climate relationships
were explored using Pearson product-moment correlation coefficients and multiple regression analysis. Radial growth at the
timberline was positively correlated with temperature in July and was also strongly correlated with mild temperatures in the
previous autumn and high precipitation in winter (January–March). At the tree line, temperatures in the previous autumn and
precipitation in late winter (March) also controlled radial growth, whereas July temperature was not significantly correlated
with ring width. Because previous autumn temperature and winter precipitation were the main growth-determining factors at
the timberline and the tree line, and both of these climate variables are known to influence susceptibility of trees to winter
stress, the results support the working hypothesis. Analysis of climatic conditions in extreme growth years confirmed the
high sensitivity of tree ring growth to precipitation in late winter (March) at the tree line plots. Furthermore, extent of
growth reduction and release varied spatially and temporarily, with south- and west-facing stands showing a higher sensitivity
to climate variation in the most recent decade (1990s) than the north-facing stand. This aspect-related change in sensitivity
to climate may be associated with effects of climate warming on cambial activity.
Keywords:
dendroclimatology, slope aspect, spatial variability, tree line, tree rings.
