Aim To evaluate the climate sensitivity of model-based forest productivity estimates using a continental-scale tree-ring network

Dendrochronology generally operates under the assumption that climate–growth relationships are age independent, once growth trends and/or disturbance pulses have been accounted for. However, several studies have demonstrated that tree physiology undergoes changes with age. This may cause growth‐related climate signals to vary over time. Using chronology statistics and response functions, we tested the consistency of climate–growth responses in tree‐ring series from Larix decidua and Pinus cembra trees of four age classes. Tree‐ring statistics (mean sensitivity, standard deviation, correlation between trees, and first principal component) did not change significantly with age in P. cembra, whereas in L. decidua they appeared to be correlated with age classes. Response function analysis indicated that climate accounts for a high amount of variance in tree‐ring widths in both species. The older the trees are, the higher the variance explained by climate, the significance of the models, and the percentage of trees with significant responses. Age influence on climate sensitivity is likely to be non‐monotonic. In L. decidua, the most important response function variables changed with age according to a twofold pattern: increasing for trees younger than 200 years and decreasing or constant for older trees. A similar pattern was observed in both species for the relationship between tree height and age. It is hypothesized that an endogenous parameter linked to hydraulic status becomes increasingly limiting as trees grow and age, inducing more stressful conditions and a higher climate sensitivity in older individuals. The results of this study confirm that the climate signal is maximized in older trees, but also that a sampling procedure non‐stratified by age (especially in multi‐aged forests) could lead to biased mean chronologies due to the higher amount of noise present in younger trees. The issue requires more extensive research as there are important ecological implications both at small and large geographic scales. Predictive modeling of forest dynamics and paleo‐climate reconstructions may be less robust if the age effect is not accounted for.

Daily stem radial growth of balsam fir [Abies balsamea (L.) Mill.] was studied between 1998 and 2001 using automated point dendrometers to investigate meteorological influence. By dividing the dendrometer daynight variation, the diurnal growth pattern was resolved into the three phases of (1) contraction, (2) expansion and (3) stem radius increment (SRI). The entire circadian cycle (4) defined by the three previous phases was considered as a fourth phase. The mean weather conditions of each phase were compared with the SRI using simple correlation and response function analysis. It was found that the weather conditions prevailing from 1600/ 1700 hours to 0800/0900 hours corresponding with the expansion-SRI phases had greater impact on SRI. Response function results confirmed most of the correlation analyses and explained up to 95% of the variance of the SRI series. Total rainfall in phases 2, 3 and 4 was correlated positively with SRI, and hence verifies the importance of daily water balance. The importance of water was also demonstrated by the negative effect of high vapour pressure deficit of phase 2, decreasing the possibility of cell radial expansion. The maximum temperature of phase 3 was the only temperature variable having a positive impact on SRI suggesting that night temperature was more important than day temperature in controlling radial growth. These results may influence the process of cell enlargement and reflect only the mechanical aspect of growth.

Summary• Tree rings are widely used long-term proxy data which, if combined with longterm instrumental climate records, can provide excellent information on global climate variability. This research aimed to determine whether interannual climategrowth responses in Alpine treeline forests are stationary over time.• We used tree-ring width chronologies of Larix decidua (European larch) from 17 sites and monthly temperatures and precipitation data for the period 1800 -1999. Climate-growth relationships were assessed with correlation and response functions, and their stationarity and consistency over time were measured using moving correlation.• Tree-ring chronologies showed similar interannual variations over the last two centuries, suggesting that the same climatic factors synchronously limited growth at most sites. The most sensitive variables showed significant transient responses varying within the time period, indicating a possible deviation from the uniformitarian principle applied to dendroclimatology.• If these findings are confirmed in future studies on other species and in other regions, we suggest that time-dependent variables should be taken into account to avoid overestimation of treeline advance, future forest carbon storage in temperaturelimited environments and inaccurate reconstruction of past climate variability.

28Climate change can modify mid to long term forest growth across a tree 29 biogeographical range. In the Mediterranean basin, the predicted increase in aridity is 30 expected to cause growth decline for several temperate tree species that are in the rear-31 edge (southernmost limit) of their distribution area. Empirical evidence suggests that the 32 forecasted growth decline seems to be site-and species-specific, but few studies have 33 considered the response of a species along its entire distribution range. We study growth 34 trends and response to climate of silver fir (Abies alba) populations across its southern 35 distribution limit in Europe. More than 1300 trees from 111 populations located across 36 Spain, Italy and Romania were used to describe growth trends using basal area 37 increment and to characterize year-to-year growth responses to climate using ring-width 38 indices. We found significant contrasting patterns of basal area increments among sites.