One of the most conspicuous characteristics of climatic landscapes in Seku destrict, on the foot of Volcano Asama and along the River Chikuma (the upper portion of River Shinano), is the very florishing growth of the lichenss on roofs of many houses in each settlement. T this region the roofs are generally covered by tiles. Except very newly built houses, they grow on almost all the roofs. The author researched their distribution and found that they are valuable indicator of the clinatic characteristics of this region. The species of the lichens there, are
paymers caperate Ach. and
Parmesia conse ter e. First, the autlaor researched the shortest ages of their, growth in each Cettl rent. For this pourpose he looked for the ages of the newest houses with lichened roofs, and desided the ages necessary for their growth. Fig-1 shows the isolines of these ages. The centre of the distribution is found on the region between Komoro and Iwamurada. Here only ten years or so are necessary for their growth, but the farther front the centre, the longer the age, and finally it is longer than thirty years in' the most outside settlements. This fact may show that the central part of this destrict has the most suitable condition for the growth of lichens, and the more outside the settlements, the worse the conditions there.
Next the author researched the situations of the lichens in each settlement, calculating the ratio between the numbers of lichened roofs and of those covered by them all of their surface. Fig-2 shows the distribution of this ratio in the destrict. The centre of the distribution is found et the region between Komoro and hwamurada, and value of the ratio anioonts to more than 35%. The more outside the settlements, the less the values of ratio, and at last they amount to only less than 20%. The situation of the distribution almost coincides with the. charactors of Fig-1.
The most necessary condition for the growth of the lichens is the fluid water, especially fog, dew etc. In this region the fog occures very frequently, especially in summer. For example it appears almost half of each month at Oiwake in summer as is shown in he Tab.-1. Bet the fog prevails in the upper portion of some tributaries rather than the lower portion in this destrict, while the growth of the lichens is more abundant in the latter. These two conflicting facts may be explained as follows. The most suitable temperature condition for the assimilation of the lichens has been said as 10-15°C and 25-30°C, and the worst condition as about 20°C. The tem-npera-ture conditions in summer, in which the fog occures most frequenly, was shown by the isothermals in Fig 3. By comparing Fig-1, -2 and -3, it becomes clear that the most predominant region of the growth of lichens coincides with the region where the mean summer temperature reaches about 23-24°C. As shown an Fig-1, this is the convergent region of the summer wind. The allows in Fig-1 show the prevailing summer wind directions estimated by many climatic landscapes, especially by the. main adhering directions of the lichens on the trees, poles etc, and it must be token into coreideretion that the fogs appear very often there.
As the conclusion, the above appointed region has the most suitable conditions for the growth of lichens concerning the fluid water and temnperature.
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