Selective Breeding of Resistant Pines against Pine Wood Nematode : Resistance of the Seedlings and the Graftings from Resistant Mother Trees

マツ枯れ激害地域の房総丘陵にある東京大学千葉演習林管内5調査林において，生き残った40～80年生の天然生または人工植栽のアカマツ，クロマツの樹幹にマツノザイセンチュウ2,000頭を接種した。3年間連続接種して枯れなかったアカマツ31本とクロマツ1本を抵抗性母樹に認定した。これらの抵抗性母樹から養苗したつぎ木苗と実生苗にマツノザイセンチュウを接種したところ，生存率は高く，強い抵抗性が再確認された。抵抗性母樹のクローンで造成した採種園から得られた実生苗は，非常に強い抵抗性を示し，マツ枯れ激害地でもほとんど枯れないテーダマツと同程度の抵抗性を示した。数系統のマツノザイセンチュウを接種しても，苗木の生存率は常に高かった。In Boso Peninsula of Chiba Prefecture, a large number of Pinus densiflora and P. thunbergii had been planted naturally or artificially, and a low rate of them survived the past heavy infestation of pine wilt disease caused by pine wood nematode, Bursaphelenchus xylophilus. P. densiflora and P. thunbergii of 40-80 years old in Tokyo Univ. Forest in Chiba were drilled on the trunks and inoculated with about 2,000 nematodes. The living trees in spite of the inoculation were repeated in the second year, and then in the following third year. The trees not killed in this repeated inoculation for three successive years were finally designated as being resistant. The graftings and the seedlings from these resistant mother trees, 31 trees of P. densiflora and 1 tree of P. thunbergii, were set for the same inoculation test, and these young trees were proved of high resistance. The graftings of these mother trees were planted in a seed orchard. By inoculation tests with several races of B. xylopilus, the seedlings bred from the orchard proved of the same strong resistance as those of Pinus taeda which was hardly killed in field by pine wilt disease

Courses of Height Growth of Cryptomeria japonica Trees Planted on a Slope : Comparison among the near ridge, the mid-slope and the near bottom in the Tokyo University Forest in Chiba

東京大学千葉演習林において，スギ造林木の樹高生長経過と土壌の理化学性およびスギ針葉の養分濃度との関係を，斜面上部，中部，下部間で比較検討した。老齢林の樹高は，斜面上部から下部にむかうにしたがって高くなる傾向がみられたが，若齢林や幼齢造林地では，上部と下部との樹高差が著しい調査地と大差ない調査地とがみられた。樹幹解析によってえた老齢林2調査地の樹高生長経過は，中，下部では，両調査地ともそれぞれ対応する地位の樹高生長曲線と似ていた。一方，上部では，20～30年生頃までは樹高生長曲線とにた生長経過であるが，その後生長が頭打ちとなる調査地と初期生長はよくないが中～後期にかけてもあまり頭打ちにならない調査地とにわかれた。中～後期にかけて生長が頭打ちであった調査地の土層は薄く，あまり頭打ちのみられなかった調査地の土層は比較的厚かった。それぞれの調査地の初期生長経過のちがいは，それぞれの老齢林を皆伐した後に植栽されたスギ苗木の生長でもみられた。土壌の化学性は，中，下部では，調査地による差が小さかった。上部では，pH値等に違いがみられ，初期生長の良い調査地の土壌は，pH値が6以上と中性にちかく，生長の劣る調査地は，相対的に酸性度の強い土壌であった。土壌の化学性は，位置的に近く，母材の同じ調査地で似ていたことから，母材の違いが影響していると考えられる。幼齢造林地での葉分析の結果，斜面上部，中部，下部で，それぞれ樹高生長のよい調査区ほど，針葉の窒素濃度が高い傾向がみられた。窒素濃度が同程度の場合，中，下部に比べて，上部で生長が劣る傾向がみられた。調査地間での土壌の理化学性の差が小さい斜面中，下部では，樹高生長経過の調査地間での差が小さく，一方，上部では，調査地間で土壌の化学性や土層の厚さ等の差が大きく，それに対応して生育初期や中～後期の樹高生長経過の調査地間の差が大きかった。Differences in course of height growth of Cryptomeria japonica trees planted on a slope were compared among near ridge, mid-slope and near bottom. The study was made in 14 study areas in the Tokyo University Forest in Chiba and causes of the difference were discussed in relation to properties of soil and nutrients contents of needle. In study areas of older stands, the height of Cryptomeria tree increased from ridge to bottom along the slope, while of younger stands and younger plantations before canopy closing, this difference was various, apparent in some cases and not apparent in other cases. On mid-slope and near bottom in the two study areas of older stands, the courses of height growth observed by stem analysis paralleled with the curves in each corresponding site class of the yield table. Near ridge, the height growth followed the yield table until 20-30-yr-old and depressed thereafter in the one area where soil layer was thinner, and the growth was not excellent in early stage but the depression with age was not obvious in the other area where soil layer was thicker. The similar difference in height growth in early stage was seen in seedlings planted on the study areas after clear-cutting of older stands. Differences in chemical properties of soil among the study areas were found near ridge, but was not apparent on mid-slope and near bottom. The height growth was affected by pH of soil, the values higher than 6 resulted in excellent growth and lower values in poor one. The chemical properties of soil depended on bed rock. In each part along the slope, the height growth increased with nitrogen content of needle. In comparison of the same level of nitrogen content, the height growths on mid-slope and near bottom were higher than near ridge. The differences in height growth between on mid-slope and near bottom were smaller reflecting smaller differences in physical and chemical properties of soil among the study areas. But near ridge the course of height growth was various throughout the earlier, middle and later stages resulting from different soil properties among the study areas

Changes in Aboveground Biomass with Age in Young Cryptomeria japonica Stands

スギ林の地上部現存量，とくに葉の現存量が林冠の閉鎖前後に，どのようにかわるかを，同じ林分で時をおってしらべた。調査林分は，東京大学千葉演習林仁ノ沢（39林班C2－1小班）所在の密度試験地の一部で，3段階の密度区画を対象とした。各区画は35m×30mの長方形で，それぞれの中央に20m×10mの継続測定区，D区（植栽密度13,333本・ha－1），M区（6,667本・ha－1），S区（3,333本・ha－1）を設置，周辺部から試料木を伐倒し，継続測定区の現存量を推定した。調査は林齢14年生（1980年）から20年生（1986年）の間に5回，いずれも5月前半におこなった。葉の現存量は林冠の閉鎖時に，一時的に大きくなる。最大値は，D区が44.4t・ha－1（16年生時），M区が42.0t・ha－1（18年生時），S区が31.2t・ha－1（15年生時）で，D区，M区では，その後，自然間引きがおこり，葉の現存量の減少がいちじるしい。立木密度が高いほど，下枝が枯れあがるので，葉が部分的に集中するが，葉密度（乾重）は1kg・m－3前後に上限がみられた。枝や幹の現存量は，木質の蓄積により林齢とともに増加する。しかし，D区の枝の現存量だけは，葉と同じように16年生時が最大，以後減少した。今後，葉の現存量がどの程度の値におちつくかは，さらに測定を継続しなければわからない。また，密度と葉の現存量の経年変化の関係を，よりあきらかにするには，同じような密度試験地での測定のくりかえしが必要である。Changes in aboveground biomass, especially in leaf biomass, of a young manmade Cryptomeria japonica forest were followed in the same plots during the period before and after canopy closing. The study plots were in a spacing experiment stand in Tokyo University Forest in Chiba and 35m×30m in rectangle, respectively, and differed in planting density; 13,333 tress・ha-1 in CrD, 6,667 trees・ha-1 in CrM, and 3,333 trees・ha-1 in CrS. The continuous study plot, 20m×10m in rectangle, was divided in the middle of each study plot; D (dense) in CrD, M (medium) in CrM, and S (sparse) in CrS. The biomasses of the plots, D, M, and S were estimated by cutting trees selected from the part around each continuous study plot, respectively. The estimations were made five times during years 1980 to 1986, i. e. 14-, 15-, 16-, 18-, and 20-year-old in stand age. The measurements in each year were made in the first half of May before the beginning of vigorous growth. A passing higher level of leaf biomass was observed when the forest canopy was closing. The maximum leaf biomass in each continuous study plot was 44.4t・ha-1 in D of 16-year-old, 42.0t・ha-1 in M of 18-year-old, and 31.2t・ha-1 in S of 15-year-old. After the maximum, the leaf biomass decreased rapidly with the beginning of natural thinning in the plots D and M. The clear length of tree increased with density, and the leaf density in the crown layer became higher. But there was a upper limit in leaf density, nearly at 1 kg dry weight・m-3. The branch and stem biomasses increased with age by accumulation of wood except the branch in D. The branch biomass in D showed a passing higher level as seen in leaf biomass. The measurements in these plots will be continued to follow the biomass in the future. Further data may be necessary for checking the effect of density on leaf biomass changes