熱帯樹とツル植物の生存における「密度依存性」を解明(Seedling Survival in Tropical Trees and Lianas)

2025-09-24 中国科学院(CAS)

中国科学院西双版納熱帯植物園の研究チームは、タイのカオヤイ国立公園にある30haの熱帯常緑林調査区で、87種の樹木と56種のつる植物(リャナ)の実生計3万6000個体の生存を追跡し、隣接個体密度が生存に与える影響を比較しました。その結果、リャナは初期段階で樹木よりも強い「同種密度依存効果(CNDD)」を受けることが判明しました。特に成木が隣接するとリャナ実生の生存率は1.2~1.8%低下したのに対し、樹木では0.3%の低下にとどまりました。また、樹木のCNDDは年ごとの変動が大きい一方、リャナでは安定していました。これは、樹木が保守的な成長戦略をとり環境変動に敏感であるのに対し、リャナは機会主義的な戦略を進化させた結果と考えられます。本研究は土壌病原菌や資源競合による密度効果がリャナ個体群を強く制御する可能性を示し、森林生態モデルに多様な植物成長型を組み込む必要性を示唆します。

<関連情報>

つる植物は、熱帯の実生の生存に関して樹木よりも強い同種の負の密度依存性を示す Lianas exhibit stronger conspecific negative density dependence than trees on tropical seedling survival

Zhenhua Sun, Nujaree Prachanun, Arunkamon Sonsuthi, Anuttara Nathalang, Wirong Chanthorn, Warren Y. Brockelman, Rong Gu, Nathan G. Swenson, Luxiang Lin
Ecology  Published: 16 September 2025
DOI:https://doi.org/10.1002/ecy.70210

熱帯樹とツル植物の生存における「密度依存性」を解明(Seedling Survival in Tropical Trees and Lianas)

Abstract

Conspecific negative density dependence (CNDD) strongly influences plant demography, especially in highly diverse tropical forests, but its relative importance may vary between growth forms. We used hierarchical Bayesian models to assess how neighbor densities affected the survival of more than 30,000 seedlings from 87 tree and 56 liana species in a tropical forest across two 1-year census intervals. Although standardized CNDD coefficients were similar between lianas and trees, lianas showed a four- to sixfold stronger per capita CNDD on seedling survival compared to trees. Specifically, adding a single conspecific neighbor (2 cm dbh at 1 m distance) reduced liana survival by -1.2% to -1.8%, whereas it only reduced tree survival by 0.3%. Nevertheless, trees exhibited greater inter-annual variation in CNDD prevalence (47%–11% of species with significant CNDD) compared to lianas (13%–23%). These contrasting patterns likely reflect growth form-specific ecological strategies in density-dependent responses to inter-annual environmental fluctuations. Our findings highlight the importance of examining per capita neighborhood effects when assessing CNDD strength and suggest that lianas and trees may utilize different mechanisms driving CNDD and exhibit varying stability in their contribution to diversity maintenance in tropical forests.

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