Our coastal forest showed little effect from the first 10 hours of exposure to salt water in June 2022 and grew normally for the rest of the year. We increased the light for 20 hours in June 2023, and the forest still looks mostly unfazed, although the tulip poplar trees draw water from the ground more slowly, which can be an early warning signal. June 2024. Poplar tulip leaves in the forest begin to brown in mid-August, a few weeks earlier than normal. In mid-September, the forest canopy is bare, as if winter has set in. This change did not happen in the plot close to which we treated the same way, but with fresh water instead of sea water. The initial resistance of our forest can be explained. partly by the relatively low amount of salt in the water in this estuary, where the water from the river is a mixture of fresh water and salty sea. The rain that fell after the experiment in 2022 and 2023 washed the salt out of the ground. The longer exposure of the trees to the saline soil after the 2024 experiment may have exceeded their ability to tolerate these conditions. And the conditions there are very dry, especially compared to our East Coast forest plots. Changes Visible in the Soil Our research group is still trying to understand all the factors that limit the tolerance of forests to salt water, and how our results apply to other ecosystems such as. as in the Los Angeles area. The leaves of the tree turning from green to brown were also a surprise before they fell, but there was another surprise hidden in the ground beneath our feet. Rainwater that seeps through the ground is usually clear, but about a month after the first saltwater exposure and just 10 hours into 2022, the ground water turned brown and stayed that way for two years. The brown color comes from dissolved carbon compounds from dead plant material. This is the same process as making tea. The water taken from the ground after one salt water experiment is the color of tea, which reflects the many compounds removed from the dead plant material. Usually, the ground water looks clear. Photo: Alice Stearns/Smithsonian Environmental Research Center, CC BY-ND
