Devereux Kendra, Rother Monica, Hawkes Andrea D, Bresnahan Philip, Corbett D Reide, Shew Roger
Department of Earth and Ocean Sciences University of North Carolina Wilmington Wilmington North Carolina USA.
Center for Marine Science University of North Carolina Wilmington Wilmington North Carolina USA.
Ecol Evol. 2025 Aug 28;15(9):e71677. doi: 10.1002/ece3.71677. eCollection 2025 Sep.
Forested, freshwater tidal wetlands in the southeastern US are dominated by bald cypresses (), which tolerate low levels of salinity. However, the response of old-growth bald cypress trees to prolonged increases in salinity remains uncertain. Bald cypress ghost forests occur along Smith Creek, a tributary of the Cape Fear River, North Carolina which has been dredged multiple times since 1871. Atop relative sea-level rise, dredging may be accelerating saltwater intrusion and ghost forest formation. To examine the effects of increased salinity on bald cypress and improve understanding of the process of ghost forest formation, we sampled trees and sediments along a salinity gradient in Smith Creek. We developed tree-ring chronologies for a high-salinity (8-12 ppt) and low-salinity (< 5 ppt) site. We quantified growth suppression patterns and climate-growth relationships at each site. Agglutinated benthic foraminifera and thecamoebians found in sediment samples served as proxies for increasing salinity over time. At the high salinity site, foraminifera began to appear at 25 cm depth in the sediment profile (indicating elevated salinity since c.1950). A lack of foraminifera at the low-salinity site indicated no major salinity increase. We identified five growth suppression events in bald cypress at the high-salinity site that were not observed at the low-salinity site (1859-1860, 1877-1887, 1946-1960, 1971-1983, 1985-2022), three of which are consistent with stress following years of dredging in the Cape Fear River (1946, 1970, 2000). The length and severity of the most recent suppression event at the high-salinity site suggests that those bald cypress are experiencing permanently stressful conditions. Additionally, monthly correlation analyses indicated that these trees may have increased sensitivity to drought and temperature. Saltwater intrusion into forested freshwater tidal wetlands induces stress in bald cypress, facilitating ghost forest formation and the loss of important ecosystem services.
美国东南部的森林淡水潮汐湿地以耐低盐度的落羽杉为主。然而，老龄落羽杉对盐度长期升高的反应仍不确定。落羽杉幽灵森林出现在北卡罗来纳州弗吉尼亚角河的一条支流史密斯溪沿岸，自1871年以来该溪已被疏浚多次。除了相对海平面上升外，疏浚可能正在加速咸水入侵和幽灵森林的形成。为了研究盐度增加对落羽杉的影响，并增进对幽灵森林形成过程的理解，我们在史密斯溪沿盐度梯度采集了树木和沉积物样本。我们为高盐度（8 - 12‰）和低盐度（<5‰）的地点建立了树木年轮年表。我们量化了每个地点的生长抑制模式和气候 - 生长关系。沉积物样本中发现的粘结底栖有孔虫和变形虫作为盐度随时间增加的代理指标。在高盐度地点，有孔虫开始出现在沉积物剖面25厘米深处（表明自约1950年以来盐度升高）。低盐度地点没有有孔虫表明盐度没有大幅增加。我们在高盐度地点的落羽杉中识别出五个生长抑制事件，而在低盐度地点未观察到（1859 - 1860年、1877 - 1887年、1946 - 1960年、1971 - 1983年、1985 - 2022年），其中三个与弗吉尼亚角河多年疏浚后的压力一致（1946年、1970年、2000年）。高盐度地点最近一次抑制事件的持续时间和严重程度表明，那些落羽杉正经历永久性的压力条件。此外，月度相关性分析表明，这些树木可能对干旱和温度的敏感性增加。咸水入侵森林淡水潮汐湿地会给落羽杉带来压力，加速幽灵森林的形成并导致重要生态系统服务的丧失。
