Abstract: Based on a 3-year (2003-2005) observation of soil heat flux (SHF) in a larch (Larix gmelinii) plantation, the characteristics of soil heat conduction in the plantation and their relationships with environment factors were analyzed. The results showed that there was an obvious seasonal variation of SHF in different years and sampling sites. The SHF was positive from April to August and mostly negative from September to next March, with an almost balance between heat income and outcome at annual scale. Solar net radiation had significant effects on the SHF and soil heat conductance (k), and an obvious time-lag effect was found, with 4-5 hours’ time-lag in winter and 2-3 hours’ time-lag in summer. Based on the real-time measurement of SHF and soil temperature difference at the study sites, the k value was significantly higher in early spring (P<0.05), but no significant difference was observed in other seasons (P>0.05). Therefore, when we use the observation data of soil temperature from weather stations to estimate soil heat flux, the k value in spring (from March to May) could induce a bias estimation.

Key words: negative air ion, spatiotemporal distribution, urban, affecting factor.