Resilience under redwoods

There’s more to redwood forests than iconic trees. On the drought-prone Central Coast, the forest understory includes a typically tropical resident—ferns.

Polystichum munitum, commonly called sword fern, is one of the most robust species of fern on California’s Central Coast. Its leaves, called fronds, are much thicker and more resilient than those of tropical ferns. Credit: Jarmila Pittermann.

Jarmila Pittermann, associate professor of ecology and evolutionary biology, and Emily Burns of Save the Redwoods League, noticed that during persistent drought, ferns’ fronds dry out and often become infested with tiny insects called thrips. To unveil drought’s physiological effects and how the ferns recover during rainy spells, Pittermann’s team studied the region’s two most abundant species of fern, Polystichum munitum and Dryopteris arguta, comparing ferns growing in the forests surrounding UCSC to potted, greenhouse specimens that they periodically dried out and rehydrated.

As reported in New Phytologist, the ferns were surprisingly resilient, but didn’t produce many fronds when it was particularly dry. Doing so would cause them to “consume their supply of water and carbohydrates too fast,” Pittermann said. The ferns can also rehydrate quickly, taking up water—including from fog—directly from their fronds, as previously shown by Burns.

“People think of ferns as inferior to angiosperms and conifers, and that’s untrue,” Pittermann said. “Ferns are holding themselves up. They have had to be resistant to make it through 350 million years of our changing planet.”

Sukee Bennett