WINTER WATER RELATIONS OF TIMBERLINE LARCH (LARIX LEPTOLEPIS GORD) ONMT FUJI

A krummholz mat of larch, Larix leptolepis, is the predominant growth form near the upper limit (near 2500 m) of the timberline ecotone on t he south slope of Mt. Fuji, Japan. On the south-eastern slope, the tre e line is lowered to 1600 m because of the last volcanic eruption. The extent and causes of winter desiccation were compared in timberline l arch between 2500 m and 1600 m elevation over two winters. Bark abrasi on due to wind-blown fine volcanic gravels caused a decrease in bark r esistance to water loss and resulted in severe desiccation damage to c urrent-year shoots of krummholz larches in the winter of 1986-87 at 25 00 m, whereas abraded shoots at 1600 m maintained high water content d uring both winters. In the winter of 1985-86, shoots of krummholz larc hes at 2500 m did not experience bark abrasion and high water contents were maintained. Experimental abrasion of shoot surfaces resulted in similar results at each elevation. Thus, in timberline larch at 2500 m , abrasion by wind-blown fine volcanic gravels is the primary factor c ausing winter desiccation damage and krummholz formation. Based on fie ld experiments, the estimated amount of water movement to non-abraded shoots was the same for the two elevations. At 2500 m, water movement to abraded shoots was less than to non-abraded shoots, but the reverse situation was noted at 1600 m. Water supply to abraded shoots at 2500 m was limited and insufficient to compensate for water loss. A cause of limited water supply at 2500 m may be xylem embolism.