Abstract ID: 3.12835 | Accepted as Poster | Poster | TBA | TBA

Wood density (WD) plays an important role in tree function and ecological performance in species inhabiting extreme environments like treelines, where climatic and mechanical constraints shape wood structure. Treeline seedlings not only endure low temperatures but also face continuous mechanical stresses, including strong winds, snow loads that may cover their stems for extended periods, and the forces associated with steep slopes in mountainous terrain. These stresses induce modifications in stem shape and wood anatomy, potentially impacting stem function. It is common for treeline gymnosperm trees to develop compression wood (CW) in mechanically stressed tissue of their stems, leading to changes in WD, strength, elasticity, and hydraulic conductivity, all of which influence ecological performance. In this study, we analyzed the WD variations in stems of Norway spruce (Picea abies) seedlings from Central European treelines with conspicuous climatic differences, focusing on high wood density areas (HWD) including unaffected latewood and compression wood (CW, which may affect earlywood, latewood, or both). We developed a novel method to quantify WD heterogeneity, allowing the estimation of low wood density (LWD, which includes stem areas with wide tracheid lumina, radial parenchyma, and resin channels) and HWD proportions. For each treeline site, to estimate and compare the means and variance of HWD, CW, and LWD proportions while quantifying uncertainty, we employed Bayesian generalized linear models. As initially hypothesized, HWD, composed predominantly of unaffected latewood and CW, remained consistent across treeline sites, accounting for approximately half of the stem cross-section. Stem eccentricity was generally high, likely due to mechanical forces such as wind and snowpack loads. Unexpectedly, high CW proportions did not consistently coincide with greater eccentricity at the whole cross-section level. CW accounted for a substantial portion of the cross-section, highlighting its possible ecological role in treeline seedling growth. Our method detects and quantifies WD variations in treeline seedlings, with potential applications extending to mature trees using radial cores or whole cross-sections. Assessing WD enhances our understanding of treeline seedlings’ structure, function, and ecological performance. Further research on severe CW proportions could improve insights into tree mechanical stability, growth, and carbon storage.