Scaling dendroecological studies on oaks combining different sampling schemes along a regional climatic gradient

Tree-rings provide the longest available quantitative records of tree and forest growth conditions at a high, annual temporal resolution. Sampling designs of dendroecological studies are typically planned for local representativity, without systematic data collection at a greater spatial scale. The integration of different sampling schemes may, however, facilitate the upscaling of findings conforming the information needs of forest planning.

In this study, we test the transferability of statistical models of the climate sensitivity of the radial growth of oaks between two complementing sampling designs and for two consecutive 30-year periods. Tree-ring width datasets are based on (i) single-core samples of 665 trees from the common oak species Quercus petraea and Q. robur collected at 520 stratified “extensive” sampling sites within a forest site classification project in Austria, and (ii) seven “intensive” sampling sites with 15 Q. petraea specimens sampled along two stem radii at each site. Both sampling designs span along a climatic gradient representing the entire climatic range of the species in Austria, approaching also the xeric edge of its distribution.

The climate sensitivity of the radial growth, defined as the strongest-on-average correlation with climatic variables, is found to be mainly driven by the climatic water balance both along the climatic gradient and during its change over two consecutive periods of analysis. The performance of the regression models on the complementing testing datasets indicates that the main patterns of climate sensitivity can be well-captured by both sampling schemes. Moreover, the intra-population variability of climate sensitivity at the “intensive” sites was comparable in its magnitude to the variability among the “extensive” sites under similar climatic conditions.

Our findings indicate that, in a regional context, the main spatiotemporal patterns of the relationships between the climatic drivers and radial growth allow for space-for-time projections under shifting climatic conditions. However, a better understanding of the intra-population variability and the temporal changes thereof can be decisive for the interpretation of dendroecological findings at different scales. Although linear estimations of the spatiotemporal variations of the climate sensitivity along the shifting climatic gradient are largely descriptive for the scope of this study, potential non-linear effects, especially in relation to the changing frequency and severity of extreme weather events may require special attention.