モミ,ツガの天然更新に関する研究(I)

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この研究はモミ,ツガ天然林を生態学的にしらべ,今後これらモミ,ツガ林の天然更新を行うさいの基礎資料を得ようとしたものである.　本研究は九州大学農学部附属宮崎地方演習林34～37林班に分布するモミ,ツガおよび落葉広葉樹よりなる天然林でおこなった.　ここでは主に稚樹の生態について報告した.　1) 地形的に見るとモミ,ツガの天然林は斜面の中腹から尾根筋に多く分布し,またモミとツガは通常混生して出現している.　2) モミ,ツガの結実の豊作は2～3年おきにあらわれているようである.　3) 稚樹の発生は5～7月に集中している.また稚樹の枯損原因は,夏の高温と冬季の土壌凍結が主因と考えられた.　4) 稚樹は母樹の少ない落葉広葉林には極めてわずかしか見られず,また母樹が多くても下層植生とくにスズタケが密生している場合には稚樹の成立が少なかった.　スズタケ群落の地床の明るさはスズタケの上の1/5から1/10の明るさで,スズタケ内に生えているモミ,ツガがスズタケの高さとほぼ等しい2.Om附近から急速な樹高生長を示していることからみて,この光不足が稚樹の生長を妨げている要因の一つと考えられた.　またスズタケの地下茎は地下20cmまでの浅い範囲に密にひろがっており,この地下茎の形態も更新を阻害する要因であろうと考えられる.　5) 樹高20cm以下の小さい稚樹の根系には樹種の特性は現われていないが,50cm以上になるとモミは深根性,ツガは浅根性を示している.　根系のひろがりから云えば,モミ,ツガは地下部分においては,よくすみわけていると云えそうである.　6) 庇陰格子試験の結果から,モミの場合庇陰度の違いによって乾物の配分の割合やT-R率が異なることがわかり,とくに庇陰度9(相対照度7.9%)以上になると光不足によって生長が極端に阻害されていた.　過度の庇陰は地上部のみならず,根系の発達を著しく阻害するようである.　また全光下においても稚樹の生長は阻害されたが,この場合は地表附近の高温土壌乾燥等が原因であろうと考えられる.　発芽当初の稚樹にとっての最適照度は80～40%附近ではないかと考えられる.The purpose of this paper is to know the actual condition of the natural reproduction of Momi (Abies firma S. et Z., Japanese fir) and Tsuga (Tsuga Sieboldii Carr., Japanese hemlock) The study was conducted at the natural forest consisted of Momi, Tsuga and some species of deciduous broad leaved trees in compartment 34-37 of Kyushu University Forest in Miyazaki. In this paper we dealed with the ecology of seedlings. The results obtained were as follows; 1) Topographically the natural forest of Momi and Tsuga distribute from the middle part of slope to the ridge and usually appear in company with. 2) It was presumed that the abundant seed years of Momi and Tsuga occur at intervals of 2-3 years. 3) The seeds of Momi and Tsuga germinated mostly from May to July and it was considered that the seedlings dies chiefly of the high temperture in Summer and frozen soil in Winter. 4) The seedlings of Momi and Tsuga were scarecely found in the deciduous broad leaves stand. In case the Suzutake group had developed in the stand, it was hardly possible to find the seedlings in the stand even if the stand was consisted of numerous mother trees. The light intensity at the ground level in the Suzutake (Sasa borealis Mak.) groups was 1/5～1/10 of the light intensity just above the foliage of Suzutake. We found that the seedlings of Momi and Tsuga elongated rapidly when the height growth exceeded at about 2.0 m height equal that of Suzutake. It was presumed that the height growth of Momi and Tsuga up to 2.0 m in the Suzutake group, had been obstructed for the insufficiency of light. And it seemed that the rhizome of Suzutake also retarded the growth of Momi and Tsuga because rhizome spreaded densely to a soil depth of about 20 cm 5) When the seedlings were very small, their root systems were similar but when the seedlings become higher than 50 cm, Momi showed the deeply rooted system in contrast with Tsuga which showed the shallowly rooted system. Judging by the root form, it is presummed that Momi and Tsuga segregate well from each other in undergroud. 6) From the results of the lattice shelter experiment of Momi seedlings, it was found that share of the dry matter produced and T-R ratio varied to the degree of shade. On account of the insufficiency of sunlight, the growth was extremely obstructed in the light below 10 % of the full sunlight. The overshading retarded not only the top growth but also the development of root. In the full sunlight, the growth of seedlings was also obstructed; the causes presumably were the high temperature at the soil surface and the soil drought etc. The optimum light intensity for the initial growth of seedling ranged from 40-80 % of the full daylight.

モミ,ツガの天然更新に関する研究(I)

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