Intra-Annual Variation of Stem Circumference of Tree Species Prevailing in Hemi-Boreal Forest on Hourly Scale in Relation to Meteorology, Solar Radiation and Surface Ozone Fluxes

(1) Background: Continuous monitoring of the tree stem increment throughout the year is crucial for the understanding of trees' reactions to changes in meteorology, solar radiation and surface ozone and evaluating the adaptive capacity of prevailing tree species to recent environmental global changes; (2) Methods: Data on tree intra-annual sequences based on electronic dendrometer data of Picea abies (L.) Karst, Pinus sylvestris L., Betula pendula, and Betula pubescens, growing under different nutritional and humidity conditions in the north-eastern part of Lithuania, together with their stem sap flow intensity, common meteorology and O-3 fluxes, were used to meet the objectives of the study; (3) Results: Stem shrinking/contraction during the day, due to transpiration, and the swelling/expansion during the night was significantly related to meteorology, sun activity and O-3 flux intensity. These variations were negatively related to current time and temperature, but positively to precipitation and relative humidity. O-3 fluxed through the stomata stimulated the shrinking process more intensively than it inhibited the swelling process, but only for pine and birch trees. Spruce trees demonstrated the highest sensitivity to O-3 impact due to its significant effect on the stem swelling process. Pine trees were less sensitive to O-3 damages and birch trees were the least sensitive. An over-moisture regime at measoeutrophic organic soil forest site increased the significance of the effect of O-3 on the tree increment of the considered tree species; (4) Conclusion: The most intensive tree ring formation of Scots pine trees in relation to recent environmental changes indicated their high resiliencies and adaptations to a local specific condition. Reduced tree growth intensity and weak relationships between the birch tree radios increment and main meteorological parameters indicated the lowest adaptive capacity of this tree species to recent environmental changes.

Automated summary

The study found that different tree species, including Norway spruce, pine, birch, and downy birch, react differently to meteorological changes, sun activity, and ozone flux. Norway spruce was the most sensitive to ozone impact, while birch trees showed the lowest adaptive capacity.