Subfossil bald cypress trees suggest localized, enduring effects of major climatic episodes on the Southeast Atlantic Coast of the United States.

Bald cypress (Taxodium distichum) is the longest-lived tree species in Eastern North America, but coastal cypress forests are vulnerable to a range of environmental factors [D. W. Stahle et al., Q. Sci. Rev. 34, 1-15 (2012)]. Here, we present analyses of bald cypress trees from a subfossil deposit at the mouth of the Altamaha River on the Georgia Coast, United States. Shifts in tree lifespans and growth rates correspond temporally to the onset of the Vandal Minimum environmental downturn, c. 500 CE. Trees that sprouted after c. 500 CE had significantly shorter lifespans on average (<200 y) than those that sprouted before this point in time (>470 y). Trees sprouting after c. 500 CE also grew significantly faster than those that sprouted before this point. Bald cypress lifespans at the Altamaha River mouth never recovered to pre-Vandal Minimum levels and, in fact, continued to decrease significantly over time. The last long-lived trees retrieved from the deposit died at the beginning of the Little Ice Age, another major climatic shift. This study suggests the enduring, localized impacts of climatic downturns and indicates the vulnerability to climate change of coastal cypress forests of the Southeast. These conclusions pertain to this location and, perhaps, other near-coastal forests. In remaining pockets of old-growth forest with bald cypress in the Southeast, 800 to 2600-y-old trees are still proven to be alive [D. W. Stahle et al., Q. Sci. Rev. 34, 1-15 (2012); D. W. Stahle et al., Environ. Res. Commun. 1, 1002 (2019)].