A tree's basal area (BA) and wood volume scale exponentially with tree diameter in species-specific patterns. Recent observed increases in tree growth suggest these allometric relationships are shifting in response to climate change, rising CO 2 levels, and/or changes in forest management. We analyzed 9,214 cores from nine conifer and 11 broadleaf species grown in managed mixed-species stands in the upper Midwest to quantify how well diameter (diameter at breast height (DBH)) serves to predict BA growth and above-ground wood and carbon (C). These samples include many large trees. We fit mixed models to predict BA growth and above-ground biomass/C from diameter, tree height, and the BA of nearby trees while controlling for site effects. Models account for 55%–83% of the variance in log(recent growth), improving predictions over earlier models. Growth-diameter scaling exponents covary with certain leaf and stem (but not wood) functional traits, reflecting growth strategies. LogBA increment scales linearly with log(diameter) as trees grow bigger in 16/20 species and growth actually accelerates in Quercus rubra L. Three other species plateau in growth. Growth only decelerates in red pine, Pinus resinosa Ait. Growth in whole-tree, above-ground biomass, and C accelerate even more strongly with diameter (mean exponent: 2.08 vs. 1.30 for BA growth). Sustained BA growth and accelerating wood/C growth contradict the common assumption that tree growth declines in bigger trees. Yield tables and silvicultural guidelines should be updated to reflect these current relationships. Such revisions will favor delaying harvests in many managed stands to increase wood production and enhance ecosystem values including C fixation and storage. Further research may resolve the relative roles of thinning, climatic conditions, nitrogen inputs, and rising CO 2 levels on changing patterns of tree growth. Graphical Abstract for Schwartzmann and Waller:Allometric equations quantify accelerated growth in trees of northeastern North AmericaTree species of northeastern North America show consistent acceleration in whole-tree above-ground carbon as they increase in tree diameter (DBH, above). Although growth rates (annual increases in basal area) vary far more among species, most species now show continued increases in growth through their largest size classes (below).

Increasing evidence suggests that fine roots are particularly sensitive to environmental changes, making them essential in responding and adapting forest ecosystems to climate change. However, we still lack a fundamental understanding of the underlying mechanisms that control fine root plasticity. The objective of this study was to determine the influence of soil moisture changes on fine root dynamics and morphology of European beech ( Fagus sylvatica L.). We conducted a 30-month study of fine root traits, i.e., fine root biomass (FRB), productivity, mortality, turnover, specific root length (SRL), specific root area (SRA), and root tip frequency (RTF), along a soil moisture gradient from dry, intermediate, and wet conditions in a near-natural mature beech forest. Sequential root coring with accompanying soil measurements was carried out at three study sites reflecting the gradient in soil water availability. For most fine root traits, we found significant differences between the upper 10 centimetres and lower soil depths. FRB showed significant differences between study sites, with the lowest FRB at the dry site. However, productivity, turnover, SRL, SRA, and RTF showed no significant differences between sites, but a high variability between seasons, suggesting an adaptation to short-term fluctuations but not to long-term gradients in soil water content (SWC). Linear mixed models revealed that decreasing SWC led to a significant increase in SRL, SRA, and RTF (standardised coefficients: −1.0 ± 0.46, −1.1 ± 0.46, and −1.1 ± 0.43, respectively). Our observations indicate an adaptation strategy of beech to low availability of soil water and drought by forming thin absorptive roots and by maintaining a high seasonal plasticity to tolerate fluctuations in soil moisture. By highlighting the belowground morphological adaptations of mature forests to low soil water availability, our results provide novel insights into the structure and dynamics of forest ecosystem adaptations to climate change.