和歌山演習林におけるモミ, ツガ林の生産力調査 : 第4報 伐採跡地に更新したミズメ若齢林について

Abstract

本報告は1, 2, 3報につづいて, 和歌山演習林の天然林, とくに伐採跡地に天然に更新した若い落葉樹林を調査し, その地上部の相対生長関係, 現存量, リター量について記述したものである。さらに, 主としてミズメについて地上部養分現存量, リターに含まれる養分量についても求めた。現存量調査は, 和歌山演習林内3林班の上腹 (標高850 - 1000m) に生立している, 更新後10数年のミズメを主とした落葉広葉樹林で, 1974年9月と1975年9月に行なわれ, さらに, 1976年5月から12月まで一生育期のリター量を求めた。集めたリターより, ミズメの葉と枝, その他広葉樹の葉と枝, 食葉性昆虫類の虫糞, 昆虫の死体, その他を選り分けた。ミズメの幹の直径と樹高に対する幹, 枝, 葉の諸量の相対生長関係はつぎのようになった。log w_s=0. 89531 log D_2・H-1.40293…(1) log V=0. 88826 log D_2・H+1. 91467…(2) log w_B=0. 92448 log D_2・H-2. 06527…(3) log w_L=0. 96357 log D_2・H-2. 41758 (A標準地)…(4) log w_L=0. 89782 log D_2・H-248048 (D標準地)…(5) log w_L=0. 87103 log D_2・H-2. 18114 (C標準地)…(6) log w_L=0. 99024 log D_2・H-2. 48173 (G標準地)…(7) w_s : 幹乾重量 kg, V : 幹材積cm_3, w_B : 枝乾重量 kg, w_L : 葉乾重量 kg, D : 胸高直径cm, H : 樹高m (1), (2), (3) 式では, 林分による分離は認められず, 調査4林分とも同一の近似式を満足した。しかし (3) 式では大きなバラツキがみられた。D_2・Hに対する葉の関係は, 林分ごとにそれぞれの相対生長関係が得られた。生枝下直径 (D_B : cm) と葉乾重量の関係は, log w_L=1. 05988 log D_B_2-1. 81276…(8) のようになり, 比較的立木密度が似ていた3林分では同一の近似式をほぼ満足した。ミズメを主とした落葉広葉樹林の現存量は, haあたり幹乾重量17 - 38ton, 幹材積34 - 73m_3, 枝乾重量4. 1 - 8. 5ton, 葉乾重量2. 2 - 4. 1tonと推定された。さらに, 葉面積は4. 1 - 5. 8ha/haとなった。1年間の幹生長量は, 調査林分のなかで最も良く生長したところで, 8. 7ton/ha・yearで, 多くは3 - 5ton/ha・yearであった。1年間のリター量はhaあたり4. 1tonで, その内訳は, ミズメ葉2. 23ton, その他の落葉広葉樹葉1. 25ton, ミズメの枝0. 33ton, 他の広葉樹の枝0. 15ton, 虫糞32. 57kg, 虫体2. 91kg, その他71. 21kgであった。虫糞量より食葉性昆虫類に摂食された葉量を推定すると約60kg/haとなり, 全葉量の2％弱に相当する。地上部の植物体の養分量は, haあたり, Nは158 - 241kg, P_2O_5は97 - 160kg, K_2Oは57 - 88kg , CaOは146 - 230kg, MgOは26 - 40kgと推定され, Nは葉に, P_2O_5, CaO, MgOは幹に多く含まれていた。リターに含まれる養分量は, haあたり, Nは127kg, P_2O_5は28kg, K_2Oは37kg, CaOは145kg, MgOは29kgと推定されたが, その90％以上が落葉に含まれていた。

This report deals with some investigations on forest production of young deciduous broad leaved trees regenerated on felling area in Kyoto University forest in WAKAYAMA (Lat. 30°04´N, Long. 135°30´E, Alt. 500 ~ 1, 200m). The investigations were carried out in forests dominated by Japanese cherry birch (Betula grossa) existed in compartment-3 (Alt. 850 ~ 1, 000m) of WAKAYAMA's forest in September, 1974 and 1975. The diameter measurment of all the trees in nine plots were carried out (Table 1). All the trees in four plots (A, C, D and G) were felled at the base, and the fresh weight of stem, branches and foliage of each tree were separately weighed. The materials for stem analysis and for determination of dry-fresh weight ratio were sampled. During eight months from May to December in 1976, five traps (50cm×50cm) were set up seventy centimeter above the ground in plot-I stand and litter fall was collected monthly. These traps made of Tetoron-cloth of fine mesh were made in the shape of a funnel. The litter was divided into the following seven fractions by hand sorting: Leaves of Betula grossa Leaves of deciduous broad leaved trees except Betula leaves Branches of Betula grossa Branches of deciduous broad leaved trees except Betula branches Faeces of herbivorous insects Dead bodies of insects Others Each fraction was oven-dried and weighed in the laboratory. 1. Each allometric relation of stem dry weight (wS, kg), stem volume (V, cm3), branch dry weight (wB, kg) and leaf dry weight (wL, kg) to D2･H (cm2･m) per a tree was shown as Fig. 1, 2, 3 and 4. Therfore, D and H represent the DBH and tree height. 2. The biomass of deciduous broad leaved stands per hectare was estimated 17 ~ 38 ton in stem dry weight, 34 ~ 73 m3 in stem volume, 4.1 ~ 8.5 ton in branch dry weight and 2.2 ~ 4.1 ton in leaf dry weight (Table 2), and leaf area was 4.1 ~ 5.8 ha/ha. Foliage biomass was within the range of that in deciduous broad leaved stands. 3. The maximum of current annual stem increment was estimated 3.3 ~ 8.7 ton/ha･year (Fig. 7). 4. The dry weight of litter fall was calculated 4.1 ton/ha from May to December, 1976. There were 2.23 ton as Betula leaf-litter, 1.25 ton as deciduous broad leaves, 0.33 ton as Betula branches, 0.15 ton as other branches, 32.57 kg as faeces of herbivorous insects, 2.91 kg as dead insects and 71.21 kg as the others per hectare (Fig. 8). 5. The primary consumption by herbivorous insects in foliage was estimated about 60 kg/ha in dry weight from May to December and that was less than 2% of leaves produced for one year. 6. The nutrient contents of upper-ground parts in young Betula grossa stands were in the range of 158 ~ 241 kg as N, 97 ~ 160 kg as P2O5, 57 ~ 88 kg as K2O, 146 ~ 230 kg as CaO and 26 ~ 40 kg as MgO per hectare (Table 3). 7. The leaf-litter of Betuia grossa had high concentration in N and CaO, and low concentration in P2O5, K2O and MgO (Fig. 9). 8. The nutrient contents of litter-fall were about 124 kg as N, 28 kg as P2O5, 37 kg as K2O, 145 kg as CaO and 29 kg MgO per hectare, and the nutrient contents of leaf-litter were more than 90% of the total (Table 4).