臺灣水鳥棲地保育的威脅與機會

Abstract

本研究聚焦在臺灣的水鳥棲地評估，在棲地威脅不斷升高與水鳥族群持續的下降的狀況下，水鳥保育工作越來越重要。臺灣位於東亞澳候鳥遷徙線的中點，臺灣西部海岸的沙質和泥質海岸為成千上萬的遷徙鳥類重要的中繼站，水鳥在遷徙過程中高度倚賴潮間帶泥灘地覓食補給與度冬，棲地的完整對於水鳥整體族群的存續至關重要。然而從上個世紀以來，臺灣的海岸地景因農業、漁業與工業的開發，地景有了大幅的改變。 為了從時間與空間尺度全面評估臺灣水鳥棲地狀態，首先分析潮間帶泥灘地在過去百年的變遷，利用歷史地形圖、Landsat衛星影像與常態化差異含水量指標 (NDWI)分析1920年代至2020年代潮間帶地景的變化。結果顯示，在1950年代以前潮間帶泥灘地面積是有所增加的，但此後逐漸減少。從1980年代起，泥灘地面積從459.72平方公里下降至194.05平方公里，從1950年代到2010年代，這60年間減少了近60%。流失的泥灘地主要轉變為住宅和商業開發（46％）、水產養殖（44％）、農業（9％）與能源生產和礦業（2％）。 人類活動區域持續的擴大，高度重疊到水鳥棲地，導致水鳥可利用區域持續的減少。為了確保自然資源的永續與保護生物多樣性，需要明確的指認出水鳥生物多樣性熱點，進行空間規劃保育。因此利用全球最大公民科學計畫eBird資料集，以1-km空間解析度系統性評估臺灣冬季水鳥分布熱點。水鳥分布熱點評估考量了物種豐富度、數量，以及國家、區域和地方重要性等五項準則。最終指認出994個水鳥熱點，其中132個、154個、137個、205個和366個網格分別符合五項、四項、三項、兩項和一項評估準則。透過分析公民科學資料，本研究有效的填補空間上的資訊空缺，並且提供一套系統化可快速評估生物多樣性分布現況的方法，可以提供生物多樣性空間治理所需的資訊。 近一步分析水鳥熱點受保護情形與棲地現況，發現只有32.60％位於保護留區內。而冬季水鳥熱點分佈區域的土地利用類型為濕地（26.66%）、水產養殖用地（22.15%）、農業（22.11%）、建物與不透水層（17.04%）、潮間帶泥灘地（7.54%）與森林（4.50%）。這亦顯示有許多水鳥的生物多樣性熱點並未受到保護，同時又座落在人類活動區域中。 在過去一個世紀中，人類活動顯著的改變了臺灣的沿海地景，從最初的潮間帶泥灘地等天然棲地組成，逐漸被人類轉變為農業與水產養殖的半天然棲地，最後因為都市與工業開發變成了完全人工化的地景。從研究結果發現傳統保護留區的局限性，無法有效的全面保護冬季水鳥生物多樣性熱點。因此，需要採取更積極與有策略的方式，以促進人與自然的共存，有必要整體評估沿海土地空間規劃與經營管理模式，以減緩水鳥棲地的流失速度，以符合現今全球生物多樣性策略目標。

Waterbird conservation is crucial due to increasing habitat threats and declining populations. This study examines the winter habitats of waterbirds and their conservation in Taiwan, situated centrally the East Asian-Australasian Flyway. The sandy/muddy shores on the western coast of Taiwan support thousands of migratory shorebirds and provide important stopover habitats. Among these habitats, tidal flats are the most crucial for shorebird survival. Migratory shorebirds rely on tidal flats for refueling and wintering. However, Taiwan’s western coast has significantly development since last century. To assess the current status of winter waterbird habitats, I evaluated landscape changes between the 1920s and 2020s using historical topographic map data, Landsat Archive images, and the Normalized Difference Water Index (NDWI). The results showed the tidal flats area increased before the 1950s but has been decreasing since the 1980s. The area has dropped rapidly from 459.72 km2 to 194.05 km2, with almost 60% of the tidal flat coverage lost in the last 60 years. The lost tidal flat areas have been converted into residential and commercial development (46%), aquaculture (44%), agriculture (9%), and energy production and mining (2%). The declining waterbird habitats and increasing overlap with human activities necessitate the identification of waterbird biodiversity hotspots for conservation management. I conducted an extensive analysis of an eBird dataset, a global citizen science initiative, to systematically evaluate the winter waterbird biodiversity hotspots at a 1-km grid scale across Taiwan. This assessment considered five criteria: species richness, abundance, and national, regional, and local importance values. I identified 994 grids as hotspots, with 132, 154, 137, 205, and 366 grids meeting all five, four, three, two, and one of the five criteria, respectively. By analyzing the crowdsourced scientific data, this study fills spatial gaps and provides a systematic method for rapidly assessing biodiversity distribution, generating up-to-date information for biodiversity management that aligns with the current status. These hotspots were mainly located in the coastal region, and only 32.60% were within the protected areas. The land-use types of these hotspot grids included wetlands 26.66%, aquaculture 22.15%, agriculture 22.11%, paved surfaces and buildings 17.04%, tidal flats 7.54%, and forests 4.50%. This implies that winter waterbird hotspots extend beyond the protected areas and significantly overlap with anthropogenic activity area. Over the past century, human activities have dramatically changed Taiwan's coastal landscape. Initially consisting of natural habitats like tidal flats, these areas have progressively been converted into semi-natural habitats for agriculture and aquaculture, and finally transformed into fully artificial landscapes. These findings highlight the limitations of traditional protected areas in effectively conserving winter waterbird hotspots. Therefore, more proactive and strategic management approaches are needed to promote sustainable coexistence between humans and nature. It is also necessary to reevaluate coastal land use plans to mitigate waterbird habitat loss, in line with the objectives of the Global Biodiversity Framework.