樹冠の年令構成に関する研究 (I) : 16年生クロマツ林について

Abstract

樹冠構造の解析の一方法としてクロマツ (Pinus Thunbergii) を用いて絶対的な時間 (年令) による数・量的な解析を試みた。調査は1971年3月, 京都大学農学部付属演習林白浜試験地の3種類の密度をもったクロマツ林分でおこなった。立木本数はヘクタールあたり40, 000本, 10, 000本, 2, 500本で40, 000本区, 10, 000本区では樹冠が閉鎖しており, 2, 500本区はまだ閉鎖が完了しておらず各々の樹冠が独立しているようであった。3林分より合計20本の試料木を伐倒して, 樹冠をつくる幹・枝を年令別に切り分けその本数, 重量を測定し, 生長量を求めた。調査結果をまとめると次のようになる。1) 生枝下直径 (D_B, cm) に対する樹冠総量 (W_C+L, g), 樹冠の非同化部分重 (W_C, g) の相対生長関係は適合度がよく, その近似式は次のようであった。log W_C+L=2. 7281 log D_B+1. 8627 log W_C=2. 7466 log D_B+1. 6953 D_Bに対する枝重 (W_B), 葉重 (W_L) の関係式は次のように近似された。log W_B=2. 8102 log D_B+1. 1731 log W_L=2. 7672 log D_B+1. 2901 2) 年令 (A) とその枝の本数 (N_A) の関係は片対数グラフで3年枝をさかいに傾きの変化する直線で近似された。傾きの変化する年令は, 樹種あるいはその樹木の着葉年数に関係があるようである。3) 年令 (A) とその枝の平均重さ (W_A) 平均太さ (D_A), 平均長さ (L_A) の間には等比級数の関係がみられ, それぞれの公比は全個体を通じてほぼ安定した値を持つようである。これらの関係式は一般に次のように表わされる。

The age composition of branch was studied for the quantitative analysis of canopy structure in Japanese black pine forest stands at Shirahama, Wakayama Pref. The practice of the investigation was carried out in three stands with different density of 40, 000, 10, 000 and 2, 500 per hectare in March 1971. 20 sample trees of various sizes were cut down at the base. Stem, branch and leaf composing the canopy were cut off separately by age, counted and weighed. The amount of volume increment was estimated by stem analysis. The results obtained were as follows: 1) The relations between total fresh weight of canopy (WC+L) and trunk diameter just below the lowest branch (DB) and between fresh weight of non-photosynthetic organ in the canopy (WC) and DB were closely correlated by linear relation in logarithmic scale (Fig. 1-1 Fig. 1-2). The relations were as follows: [Figure omitted] On the other hand, next equation was seen between number of branch of age 1 and DB, i. e, [Figure omitted] 2) The relation between logarithm of branch number of respective age (NA) and age (A) was approximated by two regression lines, in which the points changed from one to the other at the age 3. The age of the turning point of the lines seemed to be related to the species of trees or life lenght of the needles (Fig. 2-1, 2, 3). 3) Average branch weight (W¯A), average branch diameter (W¯A) and aberage branch length (W¯A) in the respective age were approximated by the geometric series concerning to the age (A), and the relations were arranged by following equations: [Figure omitted] In the equations, respective geometric ratios seemed to have some constant values in spite of difference of the density (Table 3). Namely, crown sizes of each tree seemed to have similar form in weight, and the number of one-year-old branch seemed to be proportional to the surface area of the crown of each tree. Every crown had a characteristic structure for the age composition, which was shown by some geometric series.