This is the first in a series of occasional posts I plan to write, featuring my take on one species of plant. This time the plant is the Western sword fern. For the last seven years I’ve been observing the natural world in the Pacific northwest through spring, summer, fall and winter, and I’m getting to know certain players on this verdant stage pretty well.
The Sword fern (Polystichum munitum) is a large, evergreen fern that ranges from Baja California to southeastern Alaska, mainly on the west (coastal) side of the mountain ranges. Along with enormous trees, this fern gives our forests their characteristic prehistoric look, as if a dinosaur might walk into the picture and be perfectly at home.
In the Puget Lowlands there are about 40 species of true ferns, compared to over 10,000 fern species in the world. In Skagit County, where I live, there are only a few dozen different ferns, some of which only live up in the mountains. I tell myself I should be able to find and identify all the ferns in this area. Over time, maybe I’ll get to know many of them well.
The ubiquitous Sword fern is an easy place to start.
Apart from the botanical aspects of the plant, the aesthetic aspects are also important to me – in fact when push comes to shove, the aesthetic characteristics probably move me most. Ferns are universally appealing subjects, with their simple overall shapes and repeating patterns. Sword ferns don’t have the delicate, lacy look of a typical fern; they’re big, tough evergreen plants, with fronds divided into rows of single leaflets rather than divided again and again.
This gives them a bold, graphic look.
The step-wise pattern of leaflets with their little lobes marching up the blade captivates me, but the best part is seeing what happens in spring. When new fronds emerge they uncurl upwards like other ferns, but then for no apparent reason, they appear to take a U turn. At that stage they really have a Dr. Seuss-like charm. It makes me smile with delight, every spring.
If you’ve never seen them in person, you may be surprised to learn that Sword ferns can reach heights of almost five feet (1.5 m)! Each year new fronds grow from a stout, woody rhizome in a vase-shaped arrangement. Fronds can last several years so individual plants can become quite congested.
The leaflets are lined with rows of spore dots; just one frond can release tens of millions of spores in late summer. Brush the underside of a frond with ripe spores and a fine, rust-colored powder takes flight on the wind. Reproduction in ferns is a complex process that I won’t go into here; suffice it to say that it works!
Sword ferns tolerate dryness better than many other ferns, and sunlight too, but the largest specimens grow on damper, shadier sites. Individual fronds persist for several years but if one is cut or broken, it won’t grow back. New fronds will appear in spring; over time the plant will look full again. They will colonize clear-cut areas fairly quickly, and are often a dominant understory plant in old growth forests. You’ll see them along roadsides, you’ll see them deep in the woods.
Here is my take on the Sword fern then: up close, at a distance, in color and black and white, and through all four seasons.
Postscript: For about seven years a citizen science project tracking the response of Sword ferns to changes in rainfall and moisture has been going on in California. Emily Burns, PhD discovered that fog is absorbed directly into the leaves and stems of many plants that grow in California’s Redwood forests. These forests are very dry at certain times of the year, like much of the American west coast, so plants have strategies to help procure and retain moisture. One adaptation Sword ferns use is to limit growth where there is little moisture, and grow prolifically where moisture is abundant. The resulting size differences are easily tracked, yielding data that sheds light on the effects of available moisture on plants over time. Scientists and volunteers are monitoring 11 Fern Watch sites to track Sword fern growth. Since fog frequency is declining, it’s likely that plant stress in these special habitats will increase, making it more and more important to understand where to concentrate efforts to preserve the giant Redwood trees. Data from the Fern Watch studies should be useful as people work to prioritize which Redwood forests are most resilient, and ensure that they are adequately protected.