Abstract: The stem sap flow of Schima superba was monitored continuously by using Granier’s thermal dissipation probe, and the leaf water potential of the plant was measured during three sunny days (from predawn to sunset) in wet season (August) and dry season (November), 2009. The photosynthetically active radiation above canopy, soil moisture content, air temperature, and air relative humidity were monitored simultaneously. There was a significant difference in the sap flux density on the trunk between wet and dry seasons.Besides,the sap flux density and soil water potential were highly correlated,and the correlation was much better in dry season. The ratio of leaf area to sapwood area was 0.416±0.033 m²·cm^-2, and decreased exponentially with tree height. With the decline of soil water potential in November,  the whole-tree hydraulic conductance and midday leaf water potential decreased,but not obviously. The regression analysis showed that there existed a quadratic polynomial relation between the whole-tree transpiration and leaf water potential (P<0.01), and the leaf water potential was not declined unlimitedly. The vapor pressure deficit within the surrounding air had a negative correlation with leaf water potential, but whether the air temperature and relative humidity co-affect the leaf water potential needed to be further studied.

Key words: Wanning Reservoir, entropy weigh, ecosystem health assessment, ecosystem health comprehensive index, trophic state index, principal component analysis.