The anatomical and physiological response of Scots pine xylem formation to variable water availability
We sampled three Pinus sylvestris sites along a north-south gradient of increasing drought in southern Siberia (Krasnoyarsk Krai, Russia), from 56°N to 53°N. According to Köppen-Geiger climate classification, sampling sites belong to the Dfc zone (cold continental climate). The mean annual temperature along the gradient ranged from 0.1 °C at S2 to 1.5 °C at S3, and total annual precipitation from 308 mm at S3 to 668 mm at S2.
Tree growth modeling
The combination of dendrochronological methods, tree growth modeling (VS-model) and remote sensing (MODIS, EVI) allowed to evaluate changes in P. sylvestris phenology along the studied gradient. Simulated phenology series by the VS-model were validated by EVI-derived phenological metrics over a period of fourteen years with non-significant differences for the starting of the growing season, allowing the reconstruction of longer (six decades) phenological series by the VS-model. In this sense, results suggested an advance of the starting of growing season along the whole gradient, being faster (at a rate of 5.6 days/decade) at the southern site during the recent time.
Dominant vs suppressed trees
Tree-ring, earlywood and latewood width were measured, and IADFs and resin ducts visually identified on cross-dated cores from 40 trees per site (20 dominant and 20 suppressed). The analysis showed that suppressed trees have stronger and longer climatic signals, as well as a higher occurrence of IADF and resin ducts than dominant trees. Moreover, the occurrence of analyzed xylem traits was higher at the drier site. These results highlight that suppressed trees might be more sensitive to climate, having a lower threshold for growth activation.