常緑広葉樹林の物質生産力について

Abstract

わが国の暖帯に広く分布する常緑広葉樹林の物質生産力を知る目的で, 次の4種の林分について調査を行なった。コジイ林 (熊本県, 1961年10月調査) ウバメガシ ‐ タイミンタチバナ混交林 (高知県, 1962年11月調査) アラカシ ‐ ツバキ混交林 (三重県, 1963年8月調査) ツバキ林 (三重県, 1963年8月調査) それぞれの林分に数プロットずつの標準地を設け, 胸高直径の毎木調査を行った。プロット内より合計159本の標準木を伐倒した。その後標準木について樹体各部のサイズおよび重量を測定し, それらの間に成立する相対生長関係を求めた。この結果と毎木調査の結果とから林分の樹体各部の現存量ならびに生長量を推定した。各相対生長関係については林分分離型が成立し, 特に葉量・枝量・生長量に関するものでは1林分内でも, 上層木・下層木による林分内分離が認められた。林分の幹の現存量はかなりのバラツキが認められるが, 林分平均樹高の10m前後の林分のみで比較すれば, 150ton/ha ぐらいの値となり, 樹種による差はきわめて少い。ただしツバキの林分においてはいくぶん少いようである。また林分葉量についてみると, 7 - 10ton/ha 程度となり樹種による差は非常に少い。葉面積にするとツバキ林をのぞく各林分は 8ha/ha 程度の値を示し, ツバキ林はそれより少く6ha/ha 程度の値を示す。枝の量は葉に比べると林分による差がかなり見られ 10 - 40ton/ha の値であった。幹の生長量はツバキ林 4ton/ha・yr のをのぞく林分では 10ton/ha・yr 程度の値を示し, この値は地上部の生産量にすると約25ton/ha・yr 程度の値となる。葉量, 生長量は複層林の方がいくぶん単層林に比べ多いようである。その関係と対応すると思われるが, みかけの吸光係数は複層林では0. 4, 単層林では0. 6程度となり, 複層林の方が小さい傾向がみられる。十分に閉鎖した常緑広葉樹林での物質生産力は, スギ等の人工林の物質生産力におとらないものと思われる。

The evergreen broad-leaved forest in Japan which is a dominant type widely distributed over the temperate zone was studied for their productivity of dry matter. The sample stands were chosen from four types of forests; A Castanopsis cuspidata stand, in Kumamoto Pref., in Oct. 1961. A Quercus phillyraeoides-Rapanaea neriifolia mixed stand, in Kochi Pref., in Nov. 1962. A Quercus spp.-Camellia japonica mixed stand, in Mie Pref., in Aug. 1963. A Camellia japonica stand, in Mie Pref., in Aug. 1963. In each stand, several sample plots were taken in order to measure the diameter at breast height. Sample trees were selected from the sample plots and at the ground level for further investigation. The weight of the stem, the branches and the leaves were taken separately; the total length, the diameter at breast height also were measured. The annual increment of the stem volume was enumerated by means of stem analysis. Taking the allometric equation the stem weight into account, it seemed that a single regression was applicable to the sample trees from the plots of the same type. On the other hand those of the branch weight, leaf weight and annual increment varied widely. On closer examination, these revealed the detachments of coefficent of the equation in accordance not only to the varieties of types of the stands but also to the micro-habitat or stratification. Utilizing the regression equation of allometry, the standing crop and the annual increment of stem weight of the stands were estimated in terms of tons/ha and tons/ha/year. The standing crop of the stems of the forests, whose dominant tree height averaged 10 m were estimated to total as much as 150 tons/ha in the stands other than the camellia, where lower estimate was obtained. Leaf weight ranged from 7 to 10 tons/ha. There was found no recognizable difference between the types of forests. Leaf area averaged 8 ha/ha in cases of those types of forests other than the camellia, where the leaf-area was 2 ha/ha less than that of the others. Branch weight ranged from 10 to 40 tons/ha. Marked differences between the types of forests were discernible. The annual increment of stem weight was estimated at 10 tons/ha/year with the exception of 4 tons/ha/year at the camellia stand. The annual increment of the above-ground parts of the stands was estimated at about 25 tons/ha/year. Greater leaf amount and annual increment of weight were always found in the stands of stratfied crown layers over that in the stand of single crown layers. The light extinction coefficient was 0.4 in the stratificed crown stand 0.6 in single crown stands. Generally the evergreen broad-leaved forest seems to build a stratified crown and productivity of the dry matter of the stands of this type of forest is as great as that of artificially raised Japanese cryptomeria stands.