| 摘要: | 熱帶森林是生物多樣性最高的陸地生態系統。儘管熱帶森林對人類的生存至關重要，卻經常處於威脅之中，主要是因為高強度的土地利用。本研究的目的是通過多時期的遙測影像監測技術來分析並評估中美洲尼加拉瓜波沙瓦生態保護區中核心區域的森林砍伐問題及其過程。
本研究使用了2011年，2015年和2016年的Landsat影像進行分析，並應用物件式影像分析方法(Object-based Image Analysis, OBIA)進行影像分類，用以偵測森林的覆蓋範圍，並進行森林砍伐情形之評估。結果顯示森林覆蓋面積從2011年的6206.77平方公里降至2015年的5825.14平方公里。此外本研究利用地理資訊系統(Geographic Information System, GIS)整合相關的環境圖層作為解釋因子，並應用最大熵模型(MaxEnt)以評估研究區森林砍伐之潛勢，其中包含包括完全砍伐區(砍伐後土壤裸露)與砍伐植被區(砍伐後有植生覆蓋)。本研究判釋了2015-2016年間影像中的砍伐之區塊，並使用ROC曲線(receiver operating characteristic curve)下面積，AUC(area under ROC curve)來驗證模型。模式驗證成果中，針對完全砍伐區可得AUC為0.71，植被區AUC為0.88；這些結果表明，最大熵模型可應用於評估波沙瓦核心區域內可能受到森林砍伐之區域。
模式分析結果發現，距離裸露地的遠近以及距離其他類型的植生地的遠近分別對於完全砍伐區以及砍伐植被區也最佳的解釋力，並顯示了森林砍伐過程中的不同階段：完全砍伐區為較早的階段，空間分布上有集中的情形亦有分散的狀況，而這樣的分布主要與土地的可購買與否有相關；而砍伐植被區則屬與下一個階段，其分布狀況則隨時間漸漸擴張。不論是針對完全砍伐區或者砍伐植被區的評估模式中，本研究發現距離民居社區的遠近以及距離道路、河川的遠近則對模式的解釋力無顯著的貢獻：這說明了交通、可及性等因子對於本研究區的森林砍伐問題並無明顯關聯。本研究建議，除了利用環境因子來評估雨林砍伐的問題之外，可以進一步分析砍伐區域內的區塊特性，例如： 種類、形態、演進等過程等，以期對森林砍伐議題能有更深入、更全面的了解。
;Tropical forests represent the terrestrial ecosystem with the highest biodiversity. Despite the importance of tropical forest to human species survival, these are frequently at risk, mainly because of the dynamic use of the land. The objective of this study is to assess and analyze the deforestation process in the nucleus zone of the Bosawas Biosphere Reserve, in Nicaragua, Central America, by means of remote sensing image classification and interpretation.
Landsat images from 2011, 2015 and 2016 were classified using an object-based approach. The resulting land-cover classification maps were then utilized to conduct a deforestation assessment, which revealed a loss in forest cover, going from 6206.77 km2 in 2011, to 5825.14 km2 in 2015. Moreover, with applying GIS (Geographic Information System), this study incorporated environmental factors into the Maximum Entropy model (MaxEnt) to assess areas most susceptible to deforestation, including clear-cut and vegetated areas. Deforestation patches from 2015-2016 were used to validate the models. The Area Under the Curve of Receiver Operating Curve (AUC) for the clear-cut patch model was 0.71, and 0.88 for the vegetated patch model. The results indicate that MaxEnt is a reliable method to identify the areas more likely to be affected by deforestation within the Bosawas nucleus zone.
Results show that distance to soil and distance to other types of vegetation are the most important variables for the clear-cut and vegetated patch models, respectively. This indicates that the two types of patches have different deforestation dynamics because they represent different stages of the deforestation process. Clear-cut patches belong to the early stages of deforestation, they are clustered and diffuse, and their appearance can be related to the availability of purchasable lands in the area. On the other side, vegetated patches represent more advanced phases of the deforestation process, and they tend to expand through the years. In both models, however, variables including distance to communities, roads and rivers do not show significant contribution to deforestation, meaning that accessibility is not a vital factor in the deforestation process of Bosawas. In addition to analyze the relationship between deforestation and environmental factors, to study the characteristics of the patches (e.g. morphology, type, evolution) is also suggested an important approach to broaden the understanding of the complex issue of deforestation in tropical rainforest. |
