| To elucidate the effects of inundation on the habitat of various forms of Alnus japonica in wetland areas、 the tree height、 base height and maximum root height for each A. japonica tree were investigated at 15 sites near groundwater level gauge stations in northern Japan’s Kushiro Mire. The base height in most cases was found to be above ground level. The maximum root height was equal to or above the mean water level、 suggesting that the root system may affect the habitat of A. japonica. The frequency of inundation at the maximum root heights for various periods was calculated for each tree; the results indicated that no tree over 5 m in height which inundated over a period of one week was found in trunk and sprouting types、 while some smaller than 5 m in height which inundated over three weeks were found in sprouting type tree. We also researched tree populations changing that inundated at the maximum root height as a percentage of all surveyed with different periods of continuous inundation. the results showed that the percentage of inundated trees decreased sharply over inundation periods from 12 hours or a day to one week. Trunk-form trees、 for example、 decreased from 83% to 17% over a period of continuous inundation for 12 hours to a week、 and those in sprouting form decreased from 81% to 17% over the same period. |
