圍籬排除梅花鹿啃食對墾丁高位珊瑚礁森林樹苗群落更新的影響

野放的台灣梅花鹿已對墾丁高位珊瑚礁森林的更新造成嚴重衝擊。本研究在該森林設置面積890m^2的圍籬樣區，於緊鄰處另設面積850m^2的無圍籬對照樣區，並在兩樣區都栽植易遭梅花鹿危害的12種樹苗。研究目的為比較有無梅花鹿啃食對樹苗群落之物種豐度及樹苗更新動態的影響。試驗2年期間，圍籬樣區高度≥10cm的大苗、高度＜10cm的中苗，以及新生苗的物種數與株數都提高，而對照樣區大苗及中苗該兩介量都下降，只有新生苗增加。對照樣區梅花鹿較偏好取食的大苗及中苗，數量減少的程度也都高於不好取食之樹種，但在圍籬樣區三類取食偏好的苗木數量都增加。圍籬樣區大苗的香農－威納及辛普森兩物種多樣性指數持續提高，而在對照樣區則下降。本研究發現梅花鹿對樹苗群落的啃食壓力已下達＜10cm高的低矮苗木。此外，梅花鹿對不同種樹苗的取食偏好，與先前人為餵食試驗之偏好程度具顯著正相關。對照樣區人為栽植的樹苗在短期內即遭嚴重啃食，只存活2種3株，而圍籬樣區仍存活11種120株，令整體大苗群落的香農－威納指數H'由2.51提高至2.90。結論為設置圍籬阻絕梅花鹿，可提高樹苗群落的物種豐度並維持更新，若無圍籬保護則梅花鹿較偏好取食之樹種的天然更新苗難以更新。兩年期間圍籬樣區三類形體苗木整體的豐量已增為3.4倍，顯示苗木群落恢復速度快。

關鍵字

取食偏好；圍籬樣區；天然更新；樹苗群落；多樣性指數

並列摘要

The reintroduced Formosan Sika deer has caused severe impacts to the regeneration of forest vegetation in the Kenting Karst Forest. The impacts of deer herbivory were studied by comparing the dynamics in species richness and natural regeneration of seedling communities in an exclosure plot (890 m^2) vs. an unfenced control plot (850 m^2) in the vicinity. We also planted seedlings of 12 tree species prone to deer damage in both plots. During the 2-yr investigation period, the species richness and abundance of large-sized (height ≥ 10 cm), middle-sized (height ＜ 10 cm), and emerging seedlings in the exclosure plot all increased. On the other hand, large- and middle-sized seedlings in the control plot decreased, with only emerging seedlings increasing. In the control plot, the abundance of large- and middle-sized seedlings that were highly preferred by Formosan Sika deer were more greatly reduced compared to lower-preference seedlings. However, in the exclosure plot, amounts of higher-preference seedlings of all size classes increased. Values of the Shannon-Wiener index (H') and Simpson's index of species diversity of large-sized seedlings increased in the exclosure plot, but both indices decreased in the control plot. This study found that the browsing pressure of Formosan Sika deer on seedling communities had lowered to individuals of ＜ 10 cm in height. The browsing preferences of various tree species in the karst forest were significantly related to the preferences obtained in previous artificial feeding tests. Planted seedlings in the control plot were severely browsed within a short time, and only 2 species had 3 seedlings survive. While in the exclosure plot, 120 seedlings of 11 species survived. Therefore, the value of H' of large-sized seedlings increased from 2.51 to 2.90 in the exclosure plot. In conclusion, exclosure treatment increased the species richness of the seedling community and promoted natural recruits. Natural regeneration of tree species that are highly preferred by Formosan Sika deer will be hampered if there are no fences for protection. Abundances of these 3 sizes of seedlings had increased 3.4-times 2 yr after establishing the exclosure plot. This showed that the recovery rate of the seedling community was relatively fast.

並列關鍵字

browsing preference ； exclosure plot ； natural regeneration ； seedling community ； species diversity index

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