台灣亞熱帶雨林喬木小苗之長期動態

Long-term Seedling Dynamics of Tree Species in a Subtropical Rain Forest, Taiwan

關於植物小苗新增、成活表現的研究對於了解森林的組成與動態，扮演著極為重要的角色。本研究於台灣北部的福山亞熱帶雨林（24°45’N, 121°35’E）長期監測喬木小苗的動態（2003至2010年），發現森林地被層中的小苗密度有著很大的年間變化，而此現象主要是受到研究期間每年小苗新增數量不同的影響，此外，研究期間各樹種新增苗數量上的差異與其母樹數量無關。福山地區先前的研究認為頻繁的颱風干擾導致森林冠層破碎、林下光線充足，應該有利於樹種的更新，然而我們的研究結果並不支持此一論述：絕大多數的新增小苗會在6個月內死亡，且新增小苗平均每年僅生長1.55±0.20 cm，推測可能是受到福山濃密的地被壓抑所致。研究結果顯示大多數福山的樹種都有明顯的更新限制，此一機制可能對於福山地區樹種的共存有很大的影響。小苗新增有著很大的年間變化，加上小苗的生長緩慢，這些現象再再突顯長期研究對於了解森林動態的重要性。

Knowledge of demographical rates at seedling stage is critical for understanding forest composition and dynamics. We monitored the seedling dynamics of tree species in a subtropical rain forest in Fushan, northern Taiwan (24°45’ N, 121°35’ E) during an 8-yr period (2003–2010). There were great temporal fluctuations in the seedling density, which might be largely driven by the pulses of seedling recruitment. Interspecific variation in the seedling abundance, however, was not related to the reproductive adult abundance. Previous studies showed that frequent typhoon disturbances contributed to the high canopy openness and high understory light availability at Fushan, which might benefit tree regeneration. But our results do not support this idea. Most of the newly recruited seedlings died within six months and only grew 1.55 ± 0.20 cm per year, which might be suppressed by the dense understory vegetation. Our results suggested that the majority of tree species in Fushan were recruitment limited, which might have important consequences for species coexistence. High temporal variability in recruitment density and low growth rates of seedlings emphasize the importance of long-term studies to our understandings of forest dynamics.