Radial and seasonal variation of sap flow and its response to meteorological factors in sandy Pinus sylvestris var. mongolica plantations in the Three North Shelterbelt of China

Mongolian Scots pine (Pinus sylvestris var. mongolica) is one of the main afforestation tree species in the Three North shelterbelt project in China, and an accurate estimation of its transpiration is of importance for plantation scientific density management especially under future climate change scenarios. While radial variation in tree species sap flow is an important factor for estimating transpiration, it is usually neglected. Thus, this study selected Mongolian Scots pine of different ages (10a, 20a, 30a, 40a) to study its radial variation pattern of sap flow using the multipoint (probes of different specifications) thermal dissipation method; additionally, its response characteristics to meteorological factors in northeast China were also discussed. The results show that the radial distribution of the sap flux density varied with age and growing season. It gradually decreased from the outside to the inside of the sapwood of the 10a stand. In contrast, the sap flux densities of the 20a, 30a and 40a stands had all typical single-peak patterns, with the highest value at 15 mm from the outside of the sapwood, and then sharply decreased with increasing distance. The sap flux density in both the 10a and 20a stands slightly changed, while it a significantly change in both the 30a and 40a stands between the middle and end of the growing season occurred. Further estimation of transpiration by single point and multipoint analyses was undertaken. The single point analysis resulted in large errors of -18.81%-11.02%, -52.44%-133.47%, -10.26%-130.38% and -48.78%-162.11% in the 10a, 20a, 30a and 40a stands, respectively. However, Js15mm was significantly correlated with the mean sap flux density of a sapwood area (Jsmean) and exhibited a constant conversion coefficient. The sap flux densities of separate sapwood depths were significantly affected by meteorological factors and varied according to different meteorological factors.