Fog and Redwood Forest Plants

Understanding the Physiological Consequences of Fog for Redwood Forest Plants

Emily Limm found that western sword fern absorbed the most moisture from fog. Photo by Emily Burns
Emily Limm found that western sword fern absorbed the most moisture from fog. Photo by Emily Burns

Coast redwood forests depend on fog to survive the nearly rainless summers of California’s Mediterranean climate. It was once thought that redwoods captured this moisture through their roots. But a 2004 Save the Redwoods League-funded study proved that redwoods suck up water through their leaves as well.  Intrigued by that result, Emily Burns, former University of California, Berkeley, doctoral student, set out to discover whether other plants in the redwood ecosystem were equally adept at “foliar uptake.”

In 2007, also funded by Save the Redwoods League, Limm studied 10 dominant plants in the coast redwood ecosystem, including ferns, shrubs and broadleaf and coniferous trees. She found that 8 of the 10 were able to take in water through their leaves. Limm was surprised by that result. “I didn’t think that foliar uptake was going to be unique to redwoods,” she said. “But I had no idea it would be so common.”
Limm found that western sword fern (Polystichum munitum) absorbed the most moisture from fog, but salal (Gualtheria shallon), madrone (Arbutus menziesii), tanoak (Notholithocarpus densiflorus), Douglas fir (Pseudotsuga menziesii), California huckleberry (Vaccinium ovatum), California polypody (Polypodium californicum), and, of course, redwood, were good at foliar uptake, too. By coating leaves with water, fog also helped these species conserve moisture that might have been lost through transpiration, the process of giving off water vapor through the plants’ surface pores.

Only two species in the study, California bay (Umbellularia californica) and redwood sorrel (Oxalis oregana), failed the foliar uptake test.  Limm is not sure why, but she suspects the surfaces of their leaves are different. “Water easily rolls off of it,” she said.

Now the Director of Science for Save the Redwoods League, Limm said the study may prove useful in predicting how these plants may respond to climate change. 

“As long as these plants have access to fog water, they will be able to stay hydrated,” she said. On the other hand, “Fewer fog events in the summer could have a huge effect.”

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