恆春半島地區銀合歡移除造林及其生態服務價值評估

銀合歡(Leucaena leucocephala (Lam.) de Wit)已在臺灣地區形成嚴重生態入侵(Ecological invasion)，造成原生森林生態系之服務功能衰退及喪失。政府單位長期以來對於恆春半島地區之銀合歡入侵問題，投入大量人力及費用，進行移除防治及造林復育等試驗工作，已有良好成效；然而，在進行大面積銀合歡移除造林前，對於銀合歡的抑制效果及造林復育對森林生態系服務功能的效益，應進行整合性的探討與評估。本研究以林務局屏東林區管理處於2001至2015年，所進行之銀合歡移除造林區域為研究範圍，並依據銀合歡生育環境及造林方式，共設置10個銀合歡未移除之對照樣區，及21個銀合歡移除造林樣區；依據所選擇7項評估指標所需資料，進行樣區之土壤、木本植群、地被植群及5種陸域動物等調查。藉由能值評估法進行銀合歡移除造林之森林服務價值評估；銀合歡大面積移除造林是否對於環境及銀合歡入侵族群變化有所影響方面，以無人飛行載具收集監測樣區之高解析力影像，分析銀合歡復育移除造林對水土保持的影響；並以不同期Landsat衛星分析不同時期之海岸退縮、陰陽海變化情況來探討銀合歡復育移除造林對環境衝擊之負面影響。同時透過1988、1993、1998、2003、2008、2013及2016年等7期Landsat衛星進行恆春半島銀合歡入侵面積變化分析。研究結果顯示，銀合歡經整治復育造林後，對於土壤及動植物多樣性具有顯著性差異。在土壤化學性質方面，銀合歡移除後土壤有機質從對照區0.11-0.12 g/kg提高至0.13-0.30 g/kg；動植物多樣性方面，經移除後造林約8-15年後，銀合歡重要值則降至7.7且未再發現胸徑大於5 cm以上的銀合歡入侵；透過木本植物與陸域動物Shannon-Wiener多樣性指標相關性分析結果顯示，兩者間Shannon-Wiener多樣性指標具有顯著性正相關(r=0.7217, P=0.029)，顯示木本植物多樣性增加對於陸域動物物多樣性有正面提升之效益。在生態服務效益價值評估上，銀合歡移除造林在生態服務價值估算為40,310.4-53,023.6元/ha/year，高於銀合歡未移除林相之10,495.6-19,556.0元/ha/year；其中，以碳吸存功能(61.6%)，為整體生態系服務經濟價值中最主要之項目。此外，由銀合歡入侵分佈範圍分析結果得知，目前銀合歡在恆春半島地區面積約佔5,535 ha，每年擴散速率約16.41 ha/ya-1；從各期分佈面積分析顯示，銀合歡面積自2009年開始呈現逐年下降之趨勢，其主要原因為該年度起，恆春半島地區開始進行大面積銀合歡移除造林作業。然而，此種造林方式是否對於環境造成影響，本研究利用多期衛星影像及現地調查進行分析其結果顯示，造林作業短期內會對植被及土壤沖蝕產生影響，但長期而言，銀合歡移除後重新造林會逐漸恢復水土保持之功能。以整體性之生態系服務功能及多樣性保育評估，顯示以人為方式，進行銀合歡移除，並進行造林撫育，對於銀合歡整治為一有效之措施；除能維護及提高生物多樣性外，亦可抑制銀合歡再度入侵，並有助於生態服務價值提升。

關鍵字

外來入侵植物；主動恢復；能值評估；森林生態服務；復育造林

並列摘要

The ecological invasion of Leucaena leucocephala (Lam.) de Wit has become more severe and is causing rapid decrease of native forest ecosystem services in Taiwan. With long term comprehensive efforts by the government establishments in Henchun peninsula area, the removal of L. leucocephala (Lam.) and reforestation, displayed positive results, better than before. However, few studies assess and discusses about the relationship between afforestation and the impact of ecosystem services with a large area to remove the L. leucocephala (Lam.) and reforestation. This study aims at covering the project of the afforestation on removal of L leucocephala (Lam.) de Wit carried out from 2001 to 2015 by Pingtung Forest District Office, Forestry Bureau. Based on the environment for planting and the approach for afforestation of L. leucocephala (Lam.) de Wit, a total of 10 control sample plots without having the plants removed have been established. In addition, 21 afforestation sample plots have also been set. Seven (7) assessment indexes are selected by referring to the ecosystem services and regulating services. Then, a survey is conducted to collect the information on soil, woody vegetation, understory vegetation, five terrestrial animals and so on from these sample plots for the purpose of calculating the 7 assessment indexes. In this study, the information collected from the survey on these sample plots is used to explore how different approaches for afforestation on removal of L. leucocephala (Lam.) de Wit can affect biodiversity and to what extent the depression effect is on the species. Moreover, Emergy analysis, an approach of forest ecosystem assessment, is applied to obtain the results of the afforestation on removal of L. leucocephala (Lam.) de Wit and to assess the economic value of forest services. Apart from what mentioned above, this study also attempts to discuss the effects of large-scale afforestation on removal of L. leucocephala (Lam.) de Wit on the environment and population change brought by the invasion of L leucocephala (Lam.) de Wit. In this study, Unmanned Aerial Vehicle (UAV) is arranged to collect high-resolution images of the sample plots so as to analyze how the afforestation on removal of L leucocephala (Lam.) de Wit affects soil and water conservation. Using the large-scale satellite images of the sample plots recorded by Landsat respectively in the years of 1988, 1993, 1998, 2003, 2008, 2013 and 2016, the changes in the areas invaded by this species in Hengchun Peninsula were analyzed. According to results, the removal of L. leucocephala (Lam.) de Wit demonstrate that factors including animals, plants and soil are significantly different. In terms of soil chemical properties, after the removal of L. leucocephala (Lam.) de Wit, the organic matters increase from 0.11-0.12 g/kg to 0.13-0.30 g/kg. In terms of biodiversity, woody plants and terrestrial animals within sampling areas had been investigated all year round, and the difference of biodiversity between the effects of the plantation with the removal of L. leucocephala was analyzed. The Important Value (IVI) of L. leucocephala was decreased to 7.7 after 8-15 years of afforestation. It has been transformed from a pure stand of the dominant species of L. leucocephala to a high complexity species stand, where the biodiversity index of the woody plants in the afforestation area had significantly raised than the control areas. Woody plant and terrestrial animal are positively and significantly correlated r=0.7217, P=0.029), The L. leucocephala (Lam.) de Wit has been successfully eradicated and was gradually restored with high diversity forest types, the diversity of terrestrial animal in afforestation area had significantly increased in pace with the higher vegetation diversity. The value of the ecosystem service is higher after removal and reforestation (40,310.4 to 53,023.6 NTD/ha/yr), compared to the value before removal (10,495.6 to 19,556.0 NTD/ha/yr). Overall, According to the 7 evaluation indicators, carbon sequestration service, which is the highest accounts for 61.6% of the entire ecosystem services value.The results of the distribution of L. leucocephala (Lam.) de Wit obtained from the above mentioned analysis revealed that this species currently covers an area of 5,535 ha in Hengchun Peninsula. It spreads at an annual rate of 16.41 ha ya-1. The analysis on the distribution areas in each time period demonstrated that the area covered by this species has been decreasing year by year since 2009. This mainly resulted from the large-scale afforestation on removal of L. leucocephala (Lam.) de Wit in Hengchun Peninsula starting from 2009. However, the information collected from the satellite images of different time periods and field surveys proved that the afforestation has imposed some effects on the environment. From a short-term perspective, the afforestation has produced effects on vegetation and soil erosion. On the other hand, the functions of water and soil conservation will gradually restore after the afforestation on removal of L. leucocephala (Lam.) de Wit in the future. Thus, for the ecosystem functions and biodiversity conservation, removing invasive plant, reforestation and tending by artificial process is necessary. Not only to maintain and increase the biodiversity but also inhibit alien species invasions.