颱風擾動對台灣南部墾丁森林林下光量及六種樹苗生長的影響

Effects of Typhoon Disturbances on Understory Light and Seedling Growth of Six Tree Species in a Forest at Kenting, Southern Taiwan

郭耀綸(Yau-Lun Kuo) ； 尤國霖(Gwo-Lin Yu) ； 楊月玲(Yeh-Lin Yang) ； 王相華(Hsiang-Hua Wang)

《台灣林業科學》 22卷4期 (2007/12) Pp. 367-380

https://doi.org/10.7075/TJFS.200712.0367

摘要

杜鵑颱風於2003年9月過境南台灣，本研究於颱風過後1mo，在墾丁高位珊瑚礁森林以不同程度的人工遮陰處理，探討颱風擾動後林下光資源的提高，是否可促進前生樹苗的高生長及存活率。供試6種天然更新樹苗包括毛柿、黃心柿、大葉楠、蟲屎、大葉山欖及皮孫木。試驗地森林未受颱風擾動前，林下相對光量約為1~2%；颱風過後3wk，林下光量為6~9%，3mo後樹冠層已重新長葉，光量降至2~6%，15mo後成為1~2%，顯示樹冠層已鬱閉。黃心柿苗木在1%以下低光環境生長2yr，存活率仍可維持80%以上，耐陰性極高，而大葉山欖與蟲屎則都僅有12%。供試6樹種除皮孫木外，苗木的存活率及苗高相對生長率多隨樣區內可用光資源的增多而提高，但各樹種反應的程度不同。蟲屎與黃心柿的苗高相對生長率對光資源提高的反應最明顯，毛柿與皮孫木的反應則較低。各樹苗的淨光合作用率與葉片接受到的光量均呈顯著直線正相關，廻歸線的斜率以蟲屎0.15最大，其餘5種的斜率則僅在0.04~0.07間。與遮陰處理樣區比較，杜鵑颱風過後可用光資源的增加，可提高苗木淨光合作用率及碳收穫，促進苗木高生長及減少死亡率，對林內原有前生樹苗的長期生存有助益。然此有利條件約在1yr內隨著森林冠層逐漸恢復鬱閉而減弱。

關鍵字

前生樹苗 ； 可用光資源 ； 淨光合作用率 ； 颱風擾動 ； 林下光量

並列摘要

Starting 1 mo after typhoon Dujuan swept through Taiwan in September 2003, this research manipulated the understory light availability using artificial shading treatments in the Uplifted Coral-reef Forest at Kenting, southern Taiwan. In this study, we examined the survivorship, height growth, and net photosynthetic rates of seedlings of 6 tree species with advanced regeneration for their responses to the elevated light resources after the typhoon disturbance. These species were Diospyros discolor, D. maritima, Machilus kusanoi, Melanolepis multiglandulosa, Palaquium formosanum, and Pisonia umbellifera. Understory light availability in this forest was about 1~2% before the typhoon disturbance. Three weeks after typhoon Dujuan, the understory light was 6~9%. This had dropped to 2~6% after 3 mo, when leaves had partially recovered. After 15 mo, it was again 1~2%, indicating that the canopy had again closed. Seedlings of D. maritima still maintained over 80% survival when grown under less than 1% light availability for 2 yr. However, under the same situation, Mel. multiglandulosa and Pal. formosanum could only maintain a 12% survival rate. The survival rate and relative height growth rate of each species, except for Pis. umbellifera, increased with light availability but at different magnitudes. The relative height growth rates of seedlings of Mel. multiglandulosa and D. maritima showed the most significant responses to the elevated light, while those of D. discolor and Pis. umbellifera showed the least. There were also significantly positive linear relations between the net photosynthetic rates and available light intercepted by the seedlings. The highest slope of the linear regression was 0.15 for Mel. multiglandulosa, and it ranged 0.04~0.07 for the other 5 species. Compared to the shaded plots, the increased light availability after typhoon Dujuan increased the net photosynthetic rates of these seedlings. Carbon yields likewise increased. As a result, the height growth of seedlings was promoted and mortality was reduced. This was beneficial to the long-term survival of these advanced seedlings. However, these beneficial effects diminished within 1 yr as the forest canopy gradually closed again.

並列關鍵字

advanced regeneration ； light availability ； net photosynthetic rate ； typhoon disturbance ； understory light