Departmental Bulletin Paper ミズナラ堅果生産量の長期動態と豊凶仮説の検証

來住, 牧  ,  宮, 久史  ,  吉田, 俊也  ,  植村, 滋

0073pp.125 - 132 , 2015-03-31 , 北海道大学低温科学研究所 = Institute of Low Temperature Science, Hokkaido University
北海道北部の天然林に生育するミズナラ種子生産量の年次変動の特徴を明らかにし, 種子の豊凶現象に関する至近要因仮説の適合性をGLM 解析により評価した. 各モデルのAIC 値から, 豊凶の変 動には気象要因よりも個体の資源動態が強く影響することが示唆された. 各モデルで選択された説明変数のΔAIC 値から, 前年の種子生産量が不作を誘発する負の方向への強い影響と, 花芽形成期の降水量と生育期の気温の弱い影響が認められ, 個体の内的条件が整った上で外的因子が作用することにより個体間で豊凶が同調すると考えられた.
We explored models for mast-seeding by using a set of long-term data for acorn crop from 1984 to 2011 and tree-ring records of 47 labeled trees of Mongolian oak Quercus crispula Blume growing in the Uryu Research Forest of Hokkaido University,northern Japan. We verified three dominant models for a proximate approach to mast-seeding:the weather dependence model,the resource balance model,and the combined weather-resource model. Annual acorn crop has intensely fluctuated synchronously among individuals and sites, and there was a trend towards biennial reciprocal masts, except in the consecutive extremely lean years from 1988 to 1993. The models were subjected to GLM analyses,and the AIC values indicated that the obvious fluctuations in acorn crop was strongly influenced by the inner resource dynamics of the trees, rather than the seasonal weather conditions neither in anthogenesis, fecundation, nor maturation. However, the AIC value was higher for the weather model than for the complex model, suggesting that the influence of the weather conditions was not negligible. Among the explanatory variables adopted in each model,acorn crop was the most strongly influenced by the previous crop size,and subsequently by rainfall in the previous June corresponding to the anthogenetic season negatively, and then by the current mid-summer temperature promoting maturation after fecundation. The negative correlation between acorn crop and rainfall in the previous June for the period from 1981 to 1993 was insignificant, suggesting that the phenological schedule for reproduction in this species may have changed over recent decades, possibly because of drastic changes in climate such as global warming.

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