ヒノキ人工林の物質生産の検討

Abstract

1. 綿向山々麓 (滋賀県蒲生郡日野町) に成立するヒノキ人工林について伐倒調査を行ない, その物質生産について調べた。調査林分は林令40年と30年の2林分である。両林分とも良く閉鎖し, 枝の枯れあがりも良好で, 地位に大きな差はないと思われる (表1参照)。2. 調査方法は13本 (40年生林分は7本, 30年生林分は6本) の伐倒木を1m巾の層別刈取で調べた。他にリタートラップによる落葉枝量の測定, 個体別の落葉量の測定, また樹幹解析と同じ手法による根と枝の生長量の測定を行なった。3. 林分の現存量, 生長量は樹体を構成する各器官の間に成立する相対生長関係と毎木調査結果とから推定した (表1参照)。枝生長量は40年生林分で1. 8ton/ha・yr, 30年生林分で1. 7ton/ha・yrと, 両林分に大きな差はなく, また幹生長量の約20％に相当する。30年生林分の根生長量は2. 3ton/ha・yr, トレンチ法で推定した直径2mm以下の細根量を加えると3. 0ton/ha・yrと推定された。これは根量の約6％, 幹生長量の約33％に相当する。4. 林分の純生産量 (⊿P_N) は次の2つの式から推定し, データによる推定法の検討を試みた。1) ⊿P_N=⊿y+⊿L+⊿G II) ⊿P_N=y_2N+⊿L_N+⊿G_N I) を用いると, ⊿P_Nは21. 9ton/ha・yr (40年生林分), 16. 9ton/ha・yr (30年生林分) となった。II) を用いると, 14. 9ton/ha・yr (40年生林分), 15. 9ton/ha・yr (30年生林分) となった。5. 林分の垂直構造を, 枝の生長量を中心にして論じた。地上高Z'mにおける枝の生長率をλ (Z') とすると, 両者の間に λ (Z') =α・exp 〔-β(H_max-Z')〕 の関係が認められた。ただし, α, βは定数, H_maxは林分ごとに定まる最高樹高。αは個体の優劣をあらわし, βはその林分のこみ合い方をあらわす。

1) To investigate the primary productivity and production structure of Chamaecyparis obtusa Sieb. et Zucc. forest, two test plots of even aged plantation of 40 and 30 years old and situated continuous to each other were settled. The sample trees were cut down in the fall of 1968 and analyzed. As the site quality of the two plots were seemed to be same, so the data earned by the experiments could be compared with each other. 2) The biomass of tree organs of root, branch, stem in the forests and current annual increments of dry weight of them were tabulated on table 1, which were estimated by using the allometric relations and census of experimental plots (Fig. 1, 2, 3, 4, 5, 6, 7, 8 and 9). The leaf biomasses were 19 ton/ha for 40 year-old- stand and 14 ton/ha for 30 year-old stand, in which the value of 19 ton/ha was the largest among all stands of Chamaecyparis obtusa hitherto investigated. The branch increments in dry weight were 1.8 ton/ha. yr for 40 year-old stand and 1.7 ton/ha. yr for 30 year-old stand respectively, and these values were about 20% of the stem increments. The value of dry weight increment of root was estimated about 3.0 ton/ha yr for 30 year-old stand, and its value was about 6% of root biomass and 33% of stem increment. 3) The dry weight density of stem (ys/H¯; ton/ha. m) in 40-year-old stand were larger than that in 30-year-old stand, and the value in 40-year-old stand was agreed with the maximum value theoretically derived by Dr. M. Kan. The difference of the values of the two forests seemed to be reduced to the difference of age of the stands. 4) Net primary productions (Pn; ton/ha. yr) of each stand were estimated as following [Figure omitted] Between the estimation method (1) and (2), there was little differences caused by the differences of calculation procedure of each item in the formula mentioned before (Table 2) 5) Vertical distribution patterns of weight density of each organ were discussed. Especially, the problem on the branch increment of respective layers was analysed relating to the weight density of leaf and branch. Following relation was found out between the growth rate of branch weight in respective layer (λB)Z') and height of each layer (z'; m). [Figure omitted] where α and β are constant, Hmax･. is maximum tree height. The two parameters in the above mentioned formula were analysed from the biological point of view.