Stalking The Giant Sycamore

Henry Cowell Redwoods State Park is home to the largest Western sycamores in the world, thanks to a unique combination of factors.

by Samantha Chavez

In the bright afternoon sun, I follow the entrance road into Henry Cowell Redwoods State Park. As the road opens into a meadow, I turn around to squint at the treeline that parallels Highway 9. One tree pokes above the canopies of the others.

I came to Henry Cowell looking for giant trees. Judging by the white forked branches peeking through the mass of dark and bright green leaves, I think I’ve found the one I wanted. It’s not the stately supermodel redwoods I’m searching for—it’s sycamores.

Henry Cowell has the highest concentration of giant Western sycamores found anywhere. One 157-foot-tall specimen stands in a grove along the San Lorenzo River, peering above the park’s California bay laurels and black cottonwoods. This tree is the fourth-tallest Western sycamore (Platanus racemosa) in the world. (The tallest, standing nearly 179 feet, is also found in Santa Cruz County.)

But height isn’t everything. There’s also girth to consider, and these trees have it. That 179-foot first-place recordholder, for example, is roughly half the volume of the tallest sycamore found inside the borders of Henry Cowell, according to botanist Zane Moore, who identified this grove through research he was doing on tall trees in the Santa Cruz Mountains. Moore says it’s mass that distinguishes these individuals.

“For the most part, the Henry Cowell sycamores are more than a meter in diameter and 20 cubic meters in volume,” Moore wrote Hilltromper in an email.

Hikers provide scale for this mammoth sycamore found on the River Trail at Henry Cowell. Hilltromper photo.

On a walk along the park’s River and Zayante trails, it’s easy to see that the trees here easily top 100 feet, and their stout trunks are 10 feet in circumference.

Moore also points out that the Henry Cowell grove “is special because it only contains sycamores and bay laurels that grow extremely tall without competing with redwoods.” Sycamores will get into competitions with young second-growth redwoods, climbing greater and greater heights in a race to get more sunlight. Yet the sycamores at Henry Cowell reached their extreme heights by competing primarily with bay laurels. Redwoods don’t even grow where these sycamores are growing.

It’s the San Lorenzo River and mild temperatures that give these sycamores the extra boost they need to reach stunning heights. People and trees both lose water in hot temperatures, and in sycamores the water loss stunts growth. The moderate climate here helps the trees beat the heat and retain the water that allows them to reach great heights. Furthermore, the nearby San Lorenzo raises the water table so high that the trees don’t have to expend much energy sinking their roots deep into the earth in search of water: it’s right there for the taking. It’s the perfect home for a giant Western sycamore.

More Than A Pretty Face

Sycamores are thirsty trees, and the Zayante Trail follows closely enough along the San Lorenzo River that there are bound to be sycamores growing there. And in fact, plenty stand close enough to the trail to let me get up close and personal as I walk with Henry Cowell docent Barry Grimm.

The first one we find looks 50 to 60 feet tall. I tilt my head up—and up—squinting at the light. Its younger top branches have mottled white-and-gray camouflage patterned bark. Grimm points out the older trunk of the tree, which is heavily scarred with holes created by sapsucker birds (a kind of woodpecker). I see rows of holes around the trunk and scabs of rough brown bark. The leaves by the base of the sycamores are bigger than my hand but soft as velvet. All of the leaves have three to five lobes and will be dropped by winter—crucial for the other plant communities here. “When they drop their leaves, it lets the sun shine on the understory trees like the box elder,” explains Grimm.

He turns over a leaf to show me the bristly brown clusters tucked amongst the leaves. They are the sycamore’s fruit and mark where fertilized flowers once bloomed.

The tree’s white and gray branches make for a picturesque scene, but sycamores are more than just a pretty face. Sycamores, being riverbank trees, provide nesting sites for wood ducks. As Grimm explains, “The wood ducks nest high in the sycamore. When the ducklings are ready to step into the river, they just fall out of the branches and hopefully land in the water.”

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The sycamores also provide fruit and twigs for small birds and mammals throughout the winter. They’re important for the ecosystem, so it’s a stroke of good luck that a common sycamore disease is not found in Henry Cowell.

Anthracnose is a fungal disease that destroys leaves, effectively starving the tree (since photosynthesis happens in the leaves) and stunting its growth. The disease, which so far has been found in Big Sur and the Central Valley, has not been found in the Santa Cruz Mountains.

However, notes Moore, “These trees aren’t resistant to anthracnose.” Moore took a cutting from a branch that fell from the tallest tree and planted it in another location. If the trees in the grove were resistant to the disease, then inoculating the cutting with the fungus would do nothing. But the cutting in fact contracted the disease, proving that, should anthracnose invade the Santa Cruz Mountains, the sycamores would be powerless to resist it. The fungus prefers warm dry weather, and the extended droughts combined with global warming could one day make Henry Cowell the perfect home for the fungus. According to Moore, “It won’t kill the sycamores, but it would definitely stunt them.” If the fungus finds its way into Santa Cruz, the sycamores will no longer be the giants they are now.

It’s hard for sycamores to get much public attention when they’re living in the shadow, sometimes literally, of the redwoods. Maybe we’ve gotten too used to seeing them in cities, where they decorate yards and public spaces, but the grand sycamores in Henry Cowell deserve some recognition. Their size is indicative of the years they’ve stood by the river; through the flooding of the San Lorenzo during harsh El Niño years to the droughts that plague California. Redwoods aren’t the only trees providing a healthy ecosystem for wildlife, and the thirsty sycamores are just as dependent on the San Lorenzo for water as we are. The changing climate and drop in water levels are taking the two greatest resources that the trees utilize. What this will mean for the giant Western sycamores of Henry Cowell and their other neighbors remains to be seen.

Read more about Zane Moore's research in The Tallest Redwoods in The Santa Cruz Mountains