次生林下小苗對光能的利用與耐陰性之探討

The Responses of Saplings Grown under Second Growth Forest to Light Intensity and Shade Tolerance

本研究主要藉由林下不同樹種之小苗的光反應特性，探討次生林演替後期，組成樹種中具較高重要值指數的原因。試驗樣區還在惠蓀林場第三林班長期生態研究區次生林，經選定10×20m三樣區全面調查後，計算其重要值指數，選出五種重要位指數較高之樹種，分別為變葉新木薑子、倒卵葉山龍眼、山紅柿、台灣黃杞及小葉赤楠等。為比較主要樹種與非主要樹種在林下的光照反應，另選擇台灣紅豆與狗骨仔等二樹種，以供比較，共選取了7種樹種以進行光合速率的測定。測定結果顯示變葉新木薑子、倒卵葉山龍眼與狗骨仔的耐陰性較強，山紅柿、台灣黃杞、小葉赤楠次之，而台灣紅豆則屬於不耐陰樹種，至於狗骨仔雖屬非主要樹種，其光合作用特性則表現出耐陰性樹種的特徵，因此可在冠層下生長。自上述結果顯示此林分中的主要組成樹種，在小苗階段皆可在低光量環境下適應良好，對光的捕捉及利用能力也較佳。因此，這些樹種在演替過程可逐漸佔據冠層。 For understanding in a later succession second growth forest, why some trees become dominating species. Five saplings with high importance value index (IVI) that includes Neolitsea variabillima, Helicia rengetiensis, Diospyros morrisiana, Engelhardtia roxburghiana, and Syzygium buxiiblium, moreover, two non-dominating species as Ormosia formosana, and Tricalysia dubia were used to examine the responses of photosynthetic rates to light intensity in the field. The results showed that Neolitsea variabillima, Helicia rengetiensis, and Tricalysia dubia had the higher shade tolerance among these species, Diospyros morrisiana, Engelhardtia roxburghiana, and Syzygium buxifolium ranked second. While Ormosia formosana was not a shade tolerant species. The results as above, indicated the dominating species in a later succession forest have higher shade tolerance in sapling stage, then occupy the canopy gradually during the succession process.

For understanding in a later succession second growth forest, why some trees become dominating species. Five saplings with high importance value index (IVI) that includes Neolitsea variabillima, Helicia rengetiensis, Diospyros morrisiana, Engelhardtia roxburghiana, and Syzygium buxiiblium, moreover, two non-dominating species as Ormosia formosana, and Tricalysia dubia were used to examine the responses of photosynthetic rates to light intensity in the field. The results showed that Neolitsea variabillima, Helicia rengetiensis, and Tricalysia dubia had the higher shade tolerance among these species, Diospyros morrisiana, Engelhardtia roxburghiana, and Syzygium buxifolium ranked second. While Ormosia formosana was not a shade tolerant species. The results as above, indicated the dominating species in a later succession forest have higher shade tolerance in sapling stage, then occupy the canopy gradually during the succession process.