Tidal wetland historical change by habitat class, Oregon coast, USA from 1800s to 2019

How have tidal wetlands on the Oregon coast, USA changed over the past 150-200 years? We mapped and quantified a striking and previously unrecognized coastwide alteration: the near-eradication of once-prevalent tidal forested wetlands (TFWs). We argue that this finding calls for a paradigm shift in management of Oregon’s outer coast estuaries. By combining elevation-based estuary maps and historical (1800s) vegetation data, we found that TFWs made up a majority (54%) of the coast's historical tidal wetland area, while emergent tidal wetlands ("tidal marsh") occupied a smaller area (42%). However, diking and vegetation conversion resulted in the loss of 95% of historical TFW, compared to 59% of historical tidal marsh. Tidal marsh loss was offset by a gain of 1770 ha of tidal marsh through progradation, but no similar gain occurred for TFW. The extreme loss of TFW has most likely reduced the provision of key TFW ecosystem services, such as carbon sequestration and complex, productive salmonid habitat. Restoring TFW is a high priority and can help re-establish these habitats and ecosystem services, benefiting coastal economies and ecosystems. Further research is needed to identify restoration sites with environmental conditions suitable for the establishment and long-term persistence of TFW. Identification and prioritization of potential restoration sites should account for climate change and emphasize the availability of landward migration areas and other landscape setting factors that could affect long-term persistence of TFW.美国俄勒冈州海岸的潮汐湿地在过去150至200年间发生了怎样的变化？本研究通过制图与量化分析，揭示了一项此前未被认知的显著海岸全域变化：一度广泛分布的潮汐森林湿地（Tidal Forested Wetlands, TFWs）几乎被完全清除。我们认为，这一发现要求俄勒冈州外海岸河口的管理范式发生根本性转变。本研究结合基于高程的河口地图与19世纪历史植被数据开展分析后发现，历史上该海岸的潮汐湿地中，潮汐森林湿地占比达多数（54%），而挺水潮汐湿地（emergent tidal wetlands，即潮汐盐沼）占比仅为42%，规模更小。然而，筑堤工程与植被改造导致历史上的潮汐森林湿地损失了95%，而潮汐盐沼的损失比例为59%。潮汐盐沼的损失通过海岸淤进新增的1770公顷盐沼得到了抵消，但潮汐森林湿地并未出现类似的面积增长。潮汐森林湿地的大规模流失极有可能削弱了其提供的关键生态系统服务功能，例如碳固存以及结构复杂、生产力强劲的鲑科鱼类栖息地。修复潮汐森林湿地是一项优先级极高的工作，其有助于重新建立上述栖息地与生态系统服务功能，进而惠及海岸经济与生态系统。未来仍需开展进一步研究，以识别具备适宜环境条件、可支持潮汐森林湿地建立并长期存续的修复点位。潜在修复点位的筛选与优先级排序应纳入气候变化考量，并优先保障陆向迁移区域的可获得性，同时兼顾其他可能影响潮汐森林湿地长期存续的景观格局要素。