PARENT SESSION
Poster Session 2: Forest Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Seasonal variation in xylem sap flow in relation to environmental regulation at the north-faced larch forest slope in northern Mongolia.

Iijima, Yoshihiro^*,1, Ishikawa, Mamoru¹, Kadota, Tsutomu¹, Ohata, Tetsuo¹, ¹ Institute of Observational Research for Global Change, JAMSTEC, Yokosuka, Kanagawa, Japan

ABSTRACT- The landscape in northern Mongolia varies grassland to forest from south to north with a characteristic ecotone; that is, north-faced forest slopes and south-faced grassland slopes. Intensive observation is now conducting in this area in terms of drainage energy and water cycle and its relationship with the difference in land surface environment. Objectives of the present study are to examine the transpiration from the forest slope using sap flow measurements and estimate its seasonal variation and relationship with environmental regulations. Using a cyclic heating system based on Granier method, seasonal variation in sap flow density could be estimates at the remote and non-electricity site of the larch (Larix sibirica Ledeb) forest slope from early July to late October, 2004. Mass water flux through the xylem of trees (sap flux) was estimated using sap flow density and allometric relationship between measured DBH and sap wood area. Seasonal estimation of sap flow density exhibited that canopy larch trees (over 15 m tall) had three times larger than that in subcanopy trees (less than 15 m) during mature season in July and August. Furthermore, sap flux in canopy trees showed fifteen times larger. Generally, sap flow correlated with incoming solar radiation (photosynthetically active radiation) regardless of the tree height. Seasonal variation in sap flow, however, may be affected due to some climatic signals, such as dryness and low temperature. According to soil moisture variation, it is likely that nighttime water movement appeared just after low soil moisture period. Abrupt reduction of sap flow was coincident with low temperature with less than 5 °C (late August) and 0 °C (mid-September), corresponding with the beginning of leaf coloring and leaf falling, respectively.

Key words: sap flow, water stress, Larix sibirica Ledeb, Mongolia