Short-term Effects of Leucaena Leucocephala Removal and Restoration Planting to Remaining Native Woody Plants in a Kenting Coastal Forest Restoration Site

27 Mar Short-term Effects of Leucaena Leucocephala Removal and Restoration Planting to Remaining Native Woody Plants in a Kenting Coastal Forest Restoration Site

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Abstract

墾丁國家公園內遭外來種銀合歡入侵情形嚴重，急需進行有關銀合歡移除及復舊作業的相關研究。詴驗地作業前為農耕地廢棄後遭銀合歡入侵之林地，成(幼)樹(DBH≧1cm)的密度為7,645株/ha，其中銀合歡占72%。詴驗地分為12 m與6 m兩種寬度之銀合歡移除帶，移除帶之間有3 m之保留帶，以達遮蔭及防風效果。銀合歡於2008年梅雨季前移除，並於作業前後進行現地保留原生木本植物之調查。結果顯示銀合歡移除及栽植作業不會減少成(幼)樹的密度及物種數，但會降低其樹冠面積，此外10月時冠幅的大幅下降則導因於颱風干擾。相對的，移除作業會明顯降低稚樹(DBH<1 cm，高度≧50 cm)及幼苗(高度<50 cm)的密度及物種數，且12 m移除帶的受害情形多比6 m顯著，密度減少約1/3。整體來說，銀合歡移除作業對幼小木本植物衝擊較大，移除帶越寬植生受到的影響也越大。但本研究結果顯示，多數受擾動的植生可在一個生長季內經由幼苗庫與種子庫等更新材料快速補充恢復，但未來植生更新之速度與方向，則需要進一步的監測研究。

English Abstract

Leucaena leucocephala is a widely-spread exotic invasive species that has seriously threatened the natural ecosystem in Kenting National Park. Therefore, L. leucocephala removal and native vegetation restoration are urgent issues to be addressed. A 2.2-ha experimental site, an abandoned farm, was dominated by L. leucocephala before treatment. Density of all trees with DBH≧1cm was 7,645 trees/ha, with 72% being L. leucocephala. There were two widths of removal zone, 12-m and 6-m, respectively, and a 3-m preservation zone (no L. leucocephala removal) between the removal zones. Woody plant surveys were conducted before and after removal of L. leucocephala prior to the rainy season in May 2008. Our results showed that L. leucocephala removal and restoration planting did not affect trees with DBH≧1 cm in terms of density and species richness, but canopy area of trees was reduced, especially in the 12-m removal zone. Furthermore, considerable canopy area was reduced in October as a result of typhoon disturbance. In contrast, removal of L. leucocephala significantly decreased the density and species richness of saplings (DBH<1 cm and height≧50 cm) and seedlings (height<50 cm), especially in the 12- removal zone. Average density of saplings and seedlings was reduced by 1/3. Overall, L. leucocephala removal had more impact on smaller trees. Vegetation was affected slightly more in wider removal zones. However, most of the disturbed vegetations would recover after a growing season through various regeneration sources, such as seedling bank and seed bank. Long-term monitoring is suggested to fully understand the effects of L. leucocephala removal on subsequent vegetation regeneration.