Abstract
To assess the effect of vegetation change on water balance in terms of wetland ecosystem conservation, we evaluated the evapotranspiration, the largest output from the Bibai mire, with the lysimeter method in a bamboo grass-invading area and in a Sphagnum bog. Cumulative evapotranspiration in 2004 and 2005 except for snow season was greater in the Sphagnum bog than in the bamboo grass-invading area. Therefore, we should deny a hypothesis such that because the bamboo grasses had higher ability of evapotranspiration than the indigenous plants, groundwater table lowering would take place when the bamboo grasses invaded into the Sphagnum bog, resulting in the expansion of the bamboo grass-invading area even more into the indigenous vegetation area. Based on the measured evapotranspiration rates under several groundwater table levels in the lysimeter method, we concluded that the Sphagnum growth would not be disturbed even if groundwater table level dropped down to —20 cm while the evapotranspiration rate in the bamboo grass area would be affected significantly with groundwater table level changing. And from comparison of the data from the lysimeter method with those from the other two methods, it was suggested that the lysimeter method can evaluate the evapotranspiration rate in a field scale as precisely as the Bowen ration method or the Penman method.
