Time Lag Effect on Solar Radiation of Tree Sap Flux Density for Different DBH of Larix olgensis

To clarify the role of tree characteristics and slope positions in the time lag between tree stem sap flux density (Js) and solar radiation (Rs). Plants of different diameter classes in a Larix olgensis near-mature forest (31 years old) in the hilly area of the Sanjiang Plain were used. The relationship between the time lag Js-Rs and tree characteristics, adjacent tree characteristics and slope positions was evaluated. Though both Js and Rs exhibit diurnal variation, they are not synchronized, thus leading to a time lag between Js and Rs. During the growing season, the change in Js lags behind the change in Rs by 21.1 ± 6.9 min. Compared with tree height and crown width, the time lag Js-Rs was more dependent on DBH. The time lag between Js and Rs showed a linear increase with DBH. Compared with the characteristics of neighboring trees, the time lag Js-Rs were more dependent on their own tree characteristics. A significant relationship is not observed between the time lag Js-Rs and SWC. The effects of tree characteristics, adjacent tree characteristics, and slope positions on the formation of the time lag Js-Rs were compared. The time lag of Js on Rs was mainly controlled by the tree characteristics (DBH). DBH is an important factor that affects the time lag between Js and Rs under sunny conditions during the growing season of Larix olgensis.