Growth of Secondary Forests on Serpentine Soil After Different Soil Disturbance Intensity

27 Mar Growth of Secondary Forests on Serpentine Soil After Different Soil Disturbance Intensity

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Abstract

北海道北部の音威子府村にある蛇紋岩土壌のササ地に,樹木の更新を図るために1969年に除草剤を散布し,翌年に強度を変えたかき起こしを行った。その後成立した林分について,1984年から継続的に毎木調査を行い,表土の撹乱強度と更新樹種や更新木の成長の関係を調べた。強度のかき起こしを行った強度区では多数の針葉樹の更新がみられ,弱度かき起こしの弱度区や除草剤散布のみの対照区では針葉樹はほとんど更新しなかった。しかし,強度区では針葉樹,広葉樹ともに成長が非常に悪く,健全な林分成長は期待できないことがわかった。一•方,弱度区や対照区では一般的な土壌と変わらない成長がみられ,とくに斜面下部で地位が高いと考えられる弱度区では,非常に高い成長がみられた。これらのことから,蛇紋岩土壌では,表土を剥ぎ取るような強いかき起こしを避けるべきだといえる。蛇紋岩土壌であっても,表土の撹乱をなるべく抑えた更新補助作業を行えば,一般土壌とそれほど変わらない林分成長が得られることがわかった。

English Abstract

In order to promote forest regeneration on serpentine soil, an herbicide was applied to the sasa grassland in Otoineppu, Northern Hokkaido, Japan, in 1969, followed by differing intensities of soil scarification the next year. After 1984, the site was continuously investigated to clarify the effect of soil disturbance intensity on the species composition and growth of regenerated trees. Many conifer seedlings were recruited in heavily scarified plots, but few conifers were recruited in mildly scarified or unscarified plots. In heavily scarified plots, however, the growth of both conifers and deciduous trees was very depressed, so that healthy stand growth cannot be expected. In contrast, growth after mild scarification or no scarification was as good as on ordi ry non-serpentine soil. In particular, the growth after mild scarification is superior, partly due to the higher site productivity at a relatively lower altitude as compared to other plots. In conclusion, heavy scarification must be avoided as it will remove the surface soil. Even on serpentine soil, disturbing the soil less when promoting regeneration would result in stand growth equally as high as on non-serpentine soil.