A Survey on the Early Growth of Seedlings in Restored Tropical Coastal Forest Invaded by Leucaena Leucocephala in Southern Taiwan

27 Mar A Survey on the Early Growth of Seedlings in Restored Tropical Coastal Forest Invaded by Leucaena Leucocephala in Southern Taiwan

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Abstract

外來入侵種銀合歡在墾丁國家公園已嚴重危害其自然生態，急需防治方法與原生林復舊的相關研究。本試驗地在處理前以銀合歡為優勢種，於梅雨季前採砍伐及藥劑塗抹、注射方式進行銀合歡防除後，隨即栽植八種原生樹種幼苗，並搭配輔助天然苗木更新方式，期望加速樹冠鬱蔽及恢復生物多樣性，已達到森林復舊目的。試驗處理21個月後，栽植樹種中以稜果榕與黃槿表現較佳，存活率超過70%，平均苗高淨生長量分別為200cm 及134cm，平均數冠寬度大魚1.5m，建議可作為未來熱帶海岸林就造林之架構樹種。天然更新苗中以構樹、血桐生長較佳，平均苗高勁升長量超過210cm：單株冠幅中位數超過3.5m2，此外崇史及構樹的冠面積總和大於500m2/ha。上述天然更新苗的苗高級冠幅生長較栽植苗佳，有利於銀合歡防除後樹冠層之快速恢復，除可節省復舊作業的人力與經費外，亦有助於抑制銀合歡再次入侵。因此在天然更新可用材料充足處，宜充分利用此一材料；如於天然更新材料不足或物種單純之擾動地區進行復舊，則建議配合植栽生長快速之原生樹種。

English Abstract

Leucaena leucocephala, an invasive alien species, is growing rampantly in Kenting National Park, posing serious threat to the ecosystem in the area. This study is an attempt to contribute to the research on controlling L. leucocephala and restoring the ecosystem. By the rainy season of 2004, L. leucocephala in a western coastal forest in Kenting was removed manually or by applying herbicide. Container seedlings of 8 native species were plantd, and assisted natural regeneration (ANR) method was used to hasten canopy closure and biodiversity recovery. The growth of 2 planted native species, Ficus septica and Hibiscus tiliaceus, was found to be better than the other 6 planted species after 21 months. Both species had a survival rate above 70%, and 200 cm and 134 cm in average net height growth, respectively. They also achieved an average canopy width of over 1.5m. They are recommended as framework species for tropical coastal forest restoration in the area. Among natural regenerated seedlings, Broussonetia papyrifera and Macaranga tanarius were successfully established, having over 210 cm in average net height growth. The median canopy area of individual tree of B. papyrifera, M. tanarius, and Melanolepis multigalndulosa were 7.8m2, 3.8m2, and 2.5m2, respectively. B. papyrifera and M. multiglandulosa had a total canopy area greater than 500 m2/ ha. By achieving greater growth rate and canopy area than the planted species, natural regenerated seedlings had better chance to reach canopy closure earlier and therefore may help impede the reinvasion of L. leucocephala. With added advantages of less labor and lower cost, ANR method is suggested where feasible. Supplemental planting of fast-growing native species is recommended when natural regeneration plants are inadequately available or low in diversity due to severe site degeneration.