和歌山演習林におけるモミ, ツガ林の生産力調査 : 第6報 モミ, ツガ林の下層に成立したサカキ小林分について

Abstract

本報告は, 和歌山演習林のモミ, ツガ天然林の生産力調査の一環として行なわれているもので, 上木のモミ, ツガの下層に成立しているサカキを主とした常緑広葉樹の小林分を調査し, 地上部の相対生長関係, 現存量, 地上部養分量について記述したものである。調査は, 和歌山演習林4および5林班の林班界の尾根 (標高630 - 700m) に, モミ, ツガ林の下層植生として小面積に成立している, サカキに, ヒサカキ, ウラジロガシの混ざった常緑広葉樹林を対象に, 1977年1月に行なわれた。サカキ13本, ヒサカキおよびウラジロガシ各2本, 計17本の供試木の幹, 枝, 葉の諸量を求め, 15m_2 (Plot 1), 10m_2 (Plot 2) の全立木の地上部の重量を求めた。さらに5月には, 同林分において, 2ヵ所の標準地の毎木調査を行なった。平均立木密度は, 46200本/haで, サカキが25600本/ha, ヒサカキ, ウラジロガシなどの常緑広葉樹が14240本, 落葉広葉樹が6360本で, 胸高断面積合計は6. 3m_2/haである。地上部乾物現存量は, 幹, 枝の非同化部分が, 12. 4 - 20. 4ton/ha, 葉2. 6 - 4. 3ton/haで, 平均値はそれぞれ16. 1ton/ha, 3. 6ton/ha, サカキの現存量がその約60％を占めている。葉の厚さは, サカキが最も厚く, ヒサカキ, ウラジロガシの順となり, 葉面積は, 3. 04ha/haと計算された。地上部の植物体の養分量は, 下層植生では, N 104kg/ha, P_2O_5, 23kg/ha, K_2O 83kg/ha, CaO 103kg/ha, MgO 29kg/haとなった。1年間の幹生長量は, サカキで0. 92ton/ha・yr, その他の常緑広葉樹では0. 48ton/haとなり, 単位葉乾重あたりの年間幹乾重生長量は0. 35g/g・yrと推定された。

This report deals with some investigations on forest production of evergreen broad leaved trees growing up the undergrowth of natural Japanese fir-hemlock stand in Kyoto University forest in Wakayama (Lat. 30°04′N, Long. 135°30′E, Alt. 500 ~ 1200m). The investigations were carried out in evergreen broad leaved stand dominated by Cleyra japonica in boundary of compartment-4 and 5 (Alt. 630 ~ 700m) of Wakayama's forest in January and May, 1977. In January, the diameter measurement of all the trees were carried out in two plots (plot 1 and 2). All the trees in the 15m2 and 10m2 plot area were felled at the base, and the fresh weight of stems, branches and foliage of each species were separately weighed. Additionally, thirteen Cleyra, two Eurya and two Cyclobalanopsis were felled, and stem, branches and leaves of each tree were separately weighed. And the materials for stem analysis, nutrient analysis and for determination of leaf area index and of dry-fresh weight ratio were sampled. In May, the diameter measurement of two sample plots were carried out in the same stand. Tree numbers per hectare were 46200, namely 25600 of Cleyra, 14240 of other evergreen broad leaved species and 6360 of deciduous broad leaved species, and the total basal area was 6.3 m2/ha in the same stand. Each allometric relation of stem volume (V, cm3), stem dry weight (wS, g), branch dry weight (wB, g) and leaf dry weight(wL, g) to D2･H (cm2･m) per tree was shown as Fig. 4 and 5. The biomass of upperground parts in evergreen broad leaved stand was respectively estimated at 12.4 ~ 20.4 ton (16.1 ton in mean) in stem and branch dry weight and 2.6 ~ 4.3 ton (3.6 ton in mean) in leaf dry weight per hectare. The biomass of Cleyra have been accounted for about 60 percent of that in investigated stand. Leaf area per unit dry weight of evergreen broad leaves was 80.8 cm2/g in Cleyra, 97.2 cm2/g in Eurya and 124.2 cm2/g in Cyclobalanopsis, and leaf area index of evergreen broad leaved stand was calculated 3.04 ha/ha. The nutrient contents of upperground parts in evergreen broad leaved stand were calculated 104 kg/ha of N, 22 kg/ha of P2O5, 83 kg/ha of K2O, 103 kg/ha of CaO and 29 kg/ha of MgO as shown in Table 5. Current annual stem increment was estimated at 0.92 ton/ha of Cleyra japonica and 0.48 ton/ha of the other evergreen broad leaved species. Annual stem increment per unit dry weight of evergreen leaves was estimated at 0.35 g/g･year as illustrated in Fig. 7.