摘要：Annual variation in vessel cross-section area suggests that vessels as water transport tissues in plants can adjust size and numbers according to exogenous factors, such as climate. Earlywood vessels in ring-porous species such as oak Quercus robur are considered to contain climatic signals (climatic factors influence their formation). The aim of the study was to investigate the relationship between vessel cross-sectional area and climatic factors at its northern distribution range. Living oaks growing on dry forest sites in central parts of Latvia were cored. Cores were sanded and treated with chalk to expose vessels. Earlywood vessel cross-section areas were measured for each tree-ring. Relationship between climatic factors and vessel formation was examined using correlation analysis. Earlywood vessel formation depended on spring (March, April) and annual (previous year October to current year September) temperatures. Precipitation had low influence, which is not surprising considering location close to the northern limit of distribution, but precipitation was suggested as a non- limiting factor. Climatic factors of the current year were more important for vessel formation than previous year factors
