カラマツ2代目不良造林地に関する研究

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As the planted areas of Japanese Larch (Lairx Leptlepis Gorden) increase, a phenomenon that the growth of 2nd reforestation Larch stand is extremely inferior to that of Ist stand has been caught sight of by the foresters in Nagano prefecture. This paper aims to analyse 2nd inferior stands and to extract injurious factors from them and finally to find a fundamental plan from a view of forest ecosystem. As a result of the investigation of 2nd stand amounting to 58 in number, in Nagano prefecture, in March 1959, about two thirds of them were found to be inferior stands. Of 2nd inferior stands adjoining Ist stands and similar in enviroment 11 stands were taken at random, and compared with Ist stands. The results were as follows; (a) In 2nd stands, 2 or 3 yeaes after plantation, decrease of growth was found remarkable, then dead trees appeared, their average growth volume became extremely lower than that of Ist ones, and finally we could not hope for afforestation there again. (b) Judging from the cross-section of the stumps still existing in 2nd reforestation stands, the growth volume of Ist stand seems to have been corre sponding to that of Ist or 2nd class larch stands. (c) On analysis of sample trees, as compared with Ist stands, the height growth of 2nd stands were generally found to be lower, the development of their root system much worse, and showed of a flat root system type in extent 0-15cm deep. (d) Soil types of most stands investigated were generally of a Bl_D type or B_D type, and there seemed no difference between Ist and 2nd stands in physical, especially permiative quality of soil. (e) Through careful analysis of chemical nutrient in both soil and standing crop, it was found that N, P and K of Ist stand soil were generally higher than those of 2nd, and 2nd stand soil especially in case of black soil type, contained a great deal of either Al or Fe with which P was likely to combine. If we draw a border-line distinguishing a district of snow falling above 50cm deep for a year, from a snowless or freezing district on the Nagano prefecture map, 2nd inferior stands often make appearances in the latter district. But in such a snowless or freezing district, if 2nd stands still give good growth, it is due to the fact that their mountain slopes are generally very steep, and the saturated soil water melted in late spring flows down the slopes so rapidly and outwardly that their root system does not greatly suffer from dumping-off disease. A careful analysis using flat dilution solution method, showed considerable Penicillium, Trichoderma and Mortierella in Larch stand soil, but in 2nd inferior stands the soil microfrora always fewer in sort and number, besides showed there 2 or 3 species of Fusarium often giving rise to dumping-off disease. On a test of root rot resistance, about surface and deeper layer soil of both Ist and 2nd stands, in a surface layer the resistance degree of 2nd was far lower than Ist, but in a deeper layer there was no difference between them. For the purpose of increasing the resistance degree of 2nd stands, we tried to add much lime material to it, to sterilize by heat, and to mix up their upper and lower layers, but no effective results were obtained. Putting together above results, it seems that 2nd stands are generally inferior to Ist stands, that those soil microfloras are extremely more inactive than those of Ist. These facts seem due to break-down of nutrient circle from view of forest ecosystem. So analysis of the nutrient matters of 2nd stands clear cutting of which had already been over was carried out. (a) Total amount of N in timber and others of Ist stands which have already been carried away from the forests to the outside was negligible small in comparison with that of 2nd stand soil itself. (b) On the contrary, total amount of P and K were not so lower than those of 2nd stand soil itself. Besides P generally showed a close system in nutrient circle. Consequently, we found that P contained in 2nd stand soil is insufficient for its growth. Since it became clear, as presumed, that such inferior growth of 2nd stands was due to the lack of soluble phosphorus nutrient in the soil, we attempted a phosphorus fertilizer test on the same soil. The results were as follows; (a) The more phosporus fertilizer to 2 or 3 year trees we gave, the greater they grew. (b) The same results were seen also in case of 5 or 6 year trees. (c) If the trees in the black soil were given a certain amount of fertilizer containing N, K but not P, they grew little. Therefore, in case of black soil type, the lack of phosphorus nutrient was proved. As the degree of fertilizer raised, number of soil micro-flora increased. The fact is that raising a phosphorus fertilizer only, Mortierella came out predoninant, raising nitrate only, Penicllium predominant, and those micro-floras were likely to multiply till the end of growing season. Thus there was found a considerable correlation between soil micro-flora and growth volume of forest. Under these results, it can only be said with certainty that 2nd inferior stands are an undesirable phenomenon which originates from lacking a phosphorus fertilizer and also from bad enviroment. Therefore, from the point of forest ecosystem, it is essential to bring back immediately the lost phosphorus nutrient to 2nd stand soil, and to complete the nutrient-circle ring.
信州大学農学部附属演習林の論文

カラマツ2代目不良造林地に関する研究

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信州大学農学部附属演習林 | 論文

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