天然生アカマツ林内の林冠木および亜高木の成長特性

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天然生アカマツ林施業のための基礎資料を得るため，アカマツ林内の林冠木および亜高木の胸高断面積と樹高の成長について解析を行った．対象林は九州大学宮崎演習林における天然生アカマツ林である．樹幹解析のため，樹種構成，林分密度およびサイズ構造の異なる約70年生の2林分から，アカマツ4本，モミ1本，ツガ5本，ミズナラ3本を資料木として採取した．解析の結果は以下の通りである．林冠木であるアカマツは，断面級，樹高ともに，4樹種の中で最も平均成長速度が高かった．亜高木の中ではモミの平均成長速度が高く，ツガとミズナラはほぼ同様な平均成長速度で，モミよりも緩やかに成長した．樹幹の形状比は相対的にアカマツやモミが低く，ミズナラが高い値を示した．すべての樹種において，短期的あるいは長期的に肥大成長を抑制し，伸長成長を優占する個体が確認された．また，亜高木であるツガとミズナラにおいては，生育期間途中から伸長成長が著しく抑制される個体も確認された．アカマツと他樹種の間の，断面積のサイズ差は時間とともに増大し，樹高のサイズ差はアカマツが30年あるいは40年生に至るまで増大し，その後は微増か，ほぼ一定となった．Growth, allometry, and biomass allocation to stem in canopy and sub-canopy trees in 70-year-old Pinus densilflora (Pinus) stands were studied at the Kyushu University Forest in Miyazaki. The purpose of this study was to collect basic information in order to construct a working system for natural Pinus stands. Sample trees of Pinus densiflora, Abies firma (Abies), Tsuga sieboldii (Tsuga) and Quercus mongolica var.grossesserralta(Quercus) were selected for stem analysis in the stands where tree species composition, stand density and size structure were different. The four species were compared for height and basal area growth. The results obtained were as follows. The canopy tree, Pinus had the greatest height and basal area growth rate, and sub-canopy trees of Abies, Tsuga and Quercus had a lower growth rate, The ratios of height to diameter at breast height had relatively low values for Pinus and Abies, and Quercus had the highest ratio values. For all species, there were trees whose biomass allocation to basal area growth decreased and biomass allocation to height growth increased greatly over short or long periods. Further, there were also sub-canopy trees (Tsuga and Quercus) whose biomass allocation to height growth decreased greatly. Size difference in basal area between Pinus and other species trees increased with stand development. However, size difference in height was approximately constant or increased very slowly, after size difference increased until Pinus reached 30 or 40-year-old. From these results, it was concluded that competition for light among intra-species trees and/or among inter-species trees might influence biomass allocation to stem and the growth in each species.

天然生アカマツ林内の林冠木および亜高木の成長特性

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