都市林におけるシュロとトウジュロの異常繁殖 : III 相対照度及び土壌水分のいくつかのコントロール条件下でのシュロ実生個体の生育について

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Recently rapid multiplication of Trachycarpus excelsa (PALMAE) has been observed as the undergrowth of forest in urban area. In the previous papers (Hagiwara 1977,1979), seed dispersa] by Hypsipetes amaurotis, germination period, germination rate, and distribution patterns were studied by comparisons with other floristic composition in urban area. In the present paper the author is dealing with the relation between the growth rate, drought resistance and shade tolerance which are the most important factors in the competition with other coexsisting plant. The previously germinated 720 seeds gathered from one tree were sown in each pot and pots were set under the plots of varying light intensity (full daylight, 50,10,1,O.1,and O.O1% light) and three soil moisture classes (see Fig.1,Table 1) in the early summer 1975. The herb height, leaf number, maximum leaflet number and total petiole length were measured for five growing periods at every summer or autumn. The results are as follows : 1. The survivorships in plots of dry treatment under each light intensity were under 50% at the end of the 1st year and only one individual in 50,10% light has survived untill the summer 1979 (Fig. 3). In the semi-dry and standard plots under the full daylight, 50,10,and 1% light, the some seedlings were died in the 1st year, but more than 80% survivorships were kept after that (Fig. 4). In 0.01% light plot of each moisture class all seedlings were died in the 2nd year and 0.1% in the 4th year. 2. For the growth of height showed as in figure 5,except for dry plots, the vigorous one was not 50% light but 10% light, and 1,100% light are more or less lower. In the differences between the soil moisture classes, the standard plots were higher than semi-dry plots in every light intensity. Generally the growth was slow, and even the highest individual in 10% light-standard soil moisture plot the increment was only 15cm a year, and linear growth curves were obtained in the all plots. 3. For the increasing of leaf number, it tended to arrange each plots in the same order of height growth (Fig. 6). The growth curves were linear, and coeficient of variation within each plots showed the lowest values comparing with other characters. Further more it was observed that most leaves flushed in the first growing season have remained for five years. 4. For the maximum leaflet number, in cotrast with the herb height, semi-dry plots exceede standard one in each different light intensity. The maximum value came up to 13 leaflets in the some seedlings under the 50,10% light, but under the 1% light there was no lobed leaf(Fig. 7). 5. The total petiole length represents sutably the biomass for the occupation of surroundmg space for the young aged seedlings. It increased exponentially and the coeficient of variation within plots atained more than 50%. The differences between 50,10% light and 100,1% light was found to be almost two times as long but the differences btween soil moisture classes was not clear (Fig. 8). 6. Under the extreme water deficit conditions (24.6% in summer, 53.0% in winter, indicated by maximum water capacity), the seedlings ware almost withered but under the fairly dried conditions (50.2% in summer, 66.9% in winter) those were enough to grow. From above results, we can get the estimation that the seedlings of Trachycarpus excelsa in younger stage would be tolerable when those seedlings grow under the mild conditions of forest floor. 7. The seedlings under the 1% light showed high survivorship but growth rate was extremely low, and it is not conclude that seedlings supplying 1% light under the forest floor can grow to compete with another plants. While according to the results that the seedlings of 0.1% light shaded artificialy all the year round survived for the four growing seasons, it would be safe to conclude that the physiological compensation point per individual may exsist 0.1%-1.0% relative light intensity. The conspicuous low growth rate unde
国立科学博物館の論文
1980-03-25

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萩原信介
国立科学博物館

都市林におけるシュロとトウジュロの異常繁殖 : III 相対照度及び土壌水分のいくつかのコントロール条件下でのシュロ実生個体の生育について

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