Blue is the fashion in Mediterranean pines: New drought signals from tree-ring density in southern Europe

Tree-ring blue-intensity reconstruction of the April-September maximum temperature in the Greater Caucasus region of Georgia since 1780 CE

The April-September maximum temperature in the Greater Caucasus region of Georgia has undergone notable changes, yet extended reconstructions remain scarce. We collected 40 Pinus sylvestris cores from Bakuriani and extracted their blue-intensity (BI) signals, which capture latewood density closely linked to high-season temperature. After chemical treatment and high-resolution scanning, we employed correlation analyses to identify the seasonal temperature signal in BI. Then, we used a linear regression model-validated by local instrumental records from 1950-2020-to reconstruct April-September temperatures back to 1780 CE. Additional superposed epoch analysis tested the reconstruction's responsiveness to significant volcanic eruptions and solar variability. Our reconstruction strongly correlates with observed data (r = 0.72, p < 0.001), revealing significant warming trends alongside cooling events linked to volcanic aerosols and low solar activity in recent decades. Spatial analyses confirm that the BI-derived temperature variations align well with broader regional climate patterns. Furthermore, CMIP6-based projections under high-emission scenarios suggest possible warming of up to 8.75°C by 2100, highlighting the severity of future climate risks in the region. By integrating BI data, linear regression techniques, and superposed epoch analysis, this research demonstrates the effectiveness of tree-ring proxies in capturing both anthropogenic and natural drivers of climate variability. The resulting 240-year temperature record provides valuable insights into historical climate dynamics, refines model predictions, and underscores the importance of localised, high-resolution data for adaptation planning in the Greater Caucasus region.

Temperature and Turgor "Limitation" and Environmental "Control" in Xylem Biology and Dendrochronology

Trees and other woody plants are immensely ecologically important, making it essential to understand the causes of relationships between tree structure and function. To help these efforts, we highlight persistent traditions in plant biology of appealing to environmental factors "limiting" or "controlling" woody plant features. Examples include the idea that inevitable drops in cell turgor with plant height limit cell expansion and thus leaf size and tree height; that low temperatures prohibit lignification of cells and thus the growth of woody plants at high elevation; and notions from dendrochronology and related fields that climate factors such as rainfall and temperature "control" growth ring features. We show that notions of "control," "limitation," and the like imply that selection would favor a given trait value, but that these would-be favored values are developmentally impossible to produce. Such "limitation" scenarios predict trait frequency distributions that are very narrow and are abruptly curtailed at the upper limit of developmental possibility (the right-hand side of the distribution). Such distributions have, to our knowledge, never been observed, so we see little empirical support for "limitation" hypotheses. We suggest that, as a more productive starting point, plant biologists should examine adaptation hypotheses, in which developmental possibility is wide (congruent with the wide ranges of trait variation that really are observed), but only some of the possible variants are favored. We suggest that (1) the traditional the proximate/ultimate causation distinction, (2) purging scenarios of teleology/anthropomorphism, and (3) stating hypotheses in terms of developmental potential and natural selection are three simple ways of making "limitation" hypotheses clearer with regard to biological process and thus empirically testable.