京都大学芦生演習林のブナ天然林における低木の伸長生長について

Abstract

京都大学芦生演習林のブナ天然林で, 閉鎖林冠下における低木種の伸長生長量と伸長生長パターンについて調査を行い, 伸長生長様式と栄養繁殖様式との関係及び, 株内における個々の地上茎の役割について考察を行った。結果の概要は次のとおりである。1) 年間伸長生長量の地上茎間変異が大きな種と小さな種が認められ, それらは, それぞれ萠芽更新, 伏条更新という種の栄養繁殖様式と密接な関係があるものと考えられた。2) 萠芽更新により株を維持している種については, 地上茎の地際直径の増加に伴い, 地上茎の年間伸長生長量の最大値が減少し, 萠芽地上茎の老齢化に伴う親株への養分依存量の減少が示唆された。3) 萠芽更新により株を維持しているツノハシバミ, マルバマンサク, クロモジでは, 年間伸長生長量の大きな地上茎と小さな地上茎で伸長生長のパターンに差が認められ, 年間伸長生長量の大きな地上茎では伸長期間が長かった。これは株内地上茎間での親株の養分への依存度の違いを反映しているものと考えられた。またコアジサイ, ヤマアジサイでは年間伸長生長量の大きな地上茎と小さな地上茎の伸長生長パターンの差は小さかった。主として伏条更新により株を維持しているイヌツゲ, スギでは地上茎間の伸長パターンの変異は小さかった。

Studies on the annual height increment and the course of seasonal height growth of shrubs under closed canopy were made in a natural beech forest of kyoto university forest in Ashiu. Relationships between shoot elongation characteristics and reproductive mode, and the role of each stems in a stool were discussed. The results are summerized as follows. 1) There were two types in annual height increment of shoot, one was species with large variation in the increment and another one was with small variation. Each type was mostly dependent upon the regeneration by sprouting or the regeneration by layering. 2) Maximum value of annual height increment decreased with increase of diameter at base for species regenerated by sprouting. This suggests that the degree of dependence of young sprout for resources upon parent stool changes with age. 3) Seasonal height growth pattern of stems with large annual height imcrement was different from those with small increment and the growing period of stems with large annual height increment was longer than those with small imcrement for Corylus sieboldiana, Hamamelis japonica var. obtusata and Lindera umbellata. These tendencies were also found among stems in a stool. This suggests that variation in the degree of dependence for resources upon parent stool among stems in a stool affects on the differences of the seasonal height growth pattern among stems. Little difference of seasonal height growth pattern was found between stems with large annual height increment and those with small increment for Hydrangea hirta and Hydrangea macrophylla var. acuminata. Variations in the course of seasonal height growth and in the annual height increment among stems were small for Criptomeria japonica and Ilex crenata.