The first 10 hours of exposure to salt water in June 2022 showed little effect on our coastal forest and grew normally for the rest of the year. We increased the exposure to 20 hours in June 2023, and the forest still appeared mostly unaffected, although tulip poplar tree Water was slowly being pulled from the soil, which could be an early warning sign.
Things changed after a 30-hour protest in June 2024. Tulip poplar leaves in the wild began turning brown in mid-August, several weeks earlier than usual. By mid-September the forest canopy had become bare, as if winter had arrived. These changes did not occur in a nearby plot that we treated in the same way, but with fresh water instead of seawater.
The early resilience of our forest can be partly explained by the relatively low amount of salt in the waters of this estuary, where freshwater river water and salty ocean water mix. Rainfall following the experiments in 2022 and 2023 washed the salt out of the soil.
But after the 2024 experiment there was a major drought, so salt remained in the soil then. The prolonged exposure of trees to salty soils after our 2024 experiment may exceed their ability to tolerate these conditions.
The seawater being pumped into the Southern California fires is full-strength, salty seawater. and the conditions there have become very dryEspecially compared to our east coast forest plot.
Changes in the ground are clearly visible
Our research group is still trying to understand all the factors that limit the forest's tolerance to salt water, and how our results apply to other ecosystems such as the Los Angeles area.
The leaves of the trees turning from green to brown in advance of autumn was a wonder, but the soil beneath our feet hid other surprises as well.
Rainwater seeping through the soil is usually clean, but for the first time in 2022 and after about a month of being exposed to salt water for only 10 hours, the soil water turned brown and remained that way for two years . The brown color comes from carbon-based compounds leached from dead plant material. This is a similar process to making tea.
