Of Coast Live Oaks and Oak Moths

Phryganidia californica - California oak moth and crysalis

There is an infestation this year down around Santa Cruz, of oak moth, aka oakworm moth, aka Phryganidia californica. The caterpillars are stripping all the leaves off coast live oaks (Quercus agrifolia) everywhere. My gardening friends talk of it, I've seen them on trees at nurseries, parks - and even cemeteries I've visited recently.

Oakworm moth chrysalises on the underside of an informational display at Evergreen Cemetery in Santa Cruz, a historical (and run down) cemetery of pioneer and early settler graves extending up into a steep valley.

It's quite bizarre how covered everything is in chrysalises and caterpillars on their way to that state.

Yet, people are not that bothered. Even this article in Santa Cruz Sentinel recently is pretty laid back about them. In fact, gardener friends tell me that their oaks come back even better than before. But they also mention how very unpleasant it is to be pooped on by the caterpillar frass, which falls from the trees with the pitter patter of a light rain. The caterpillars are voracious.

Just a few leaves to go...

They munch all the leaves on one oak, them move on to the next. In this picture the oak on the left is not yet badly hit, yet the one on the right is denuded.

Small oaks at Arana Gulch open space park in Santa Cruz (just behind Santa Cruz Harbor)

So far, we have not seen them up here on the ridge - they seem to be staying coastal. I hope it stays that way. Earlier this year I pruned some little oaks.

Small oaks along our road - in mid haircut

And post-haircut. I don't like them limbed up so, especially since I couldn't bring myself to remove the coffeeberry growing under them - so the lollipopping really has no point, in terms of keeping fire from getting up into the canopy. They are sprouting along the trunk a little bit now though. And not leaning into the road so much. 

Coast live oaks can occur in various forms, depending on the situation they are born into. The ones I pruned are in chaparral habitat. Very thin soil. They also like rich riparian soil.

Here are some oaks in a nearby riparian zone. They grow tall and lanky.

Close to the coast, the trees that grow along rivers are almost exclusively arroyo willow Farther inland, and on the upper slopes of a river, oaks predominate, and California sycamore. Along our higher elevation creek, there is a lot of big leaf maple.


Oak woodland is the climax plant community on the coastal terrace, on which Santa Cruz is built. Also on the second coastal terrace up a level from the city streets. These terraces used to be the sea floor at some point long ago. Climax -- that means that it's the final plant community -- until another fire starts the succession through grassland, shrubs, to woodland going all over again.

First cut of a vegetation map of Santa Cruz built up areas. Yellow indicates the first costal terrace and beige the second coastal terrace that is visible (updates to this graphic are TBD).

I recently began working with Randall Morgan, local renowned naturalist, on mapping out the types of vegetation that would exist in Santa Cruz, if it were not built up. Above is the first cut of the vegetation map. It is created from a map marked up by Randall and turned into a graphic by the kindness of Bill Henry, a biologist working on the West Cliff Coastal Bluff restoration project (that's another story!). He has SGIS software that enables him to add layers onto a topo type map.

The situation of California plant communities, especially grassland types, is complicated by the fact that before the settlers came here, the First People had been managing the land for thousands of years, burning regularly to maintain good production of bulbs and other edible perennials. The burning kept the coastal terraces and other grasslands in their post-fire state of being, with the exception of some large oaks.

After the Spanish, Mexicans, and Americans came along, the burning was stopped. Now the oaks are encroaching, as the natural succession of vegetation types after a fire takes its natural course. Except of course where the ground has been used for agriculture and development of housing.  So if you garden in the city of Santa Cruz and want to recreate a local plant community, you can choose coastal prairie plant community, or oak woodland, or a mixture, with some shrubs too (coyote brush is common). And you can throw a little riparian habitat in on the shady side of your house, too, if you want to splurge a bit of irrigation.

Coast live oaks in good soil grow magnificently to huge proportions, given 200 years or more. They are wide and sprawl all over the place where they have the room. Their long lower limbs often recline languidly on the ground. Here are a few from the second coastal prairie areas of Santa Cruz, mostly in Arana Gulch open space, just above the Santa Cruz Harbor.

Wonderful trees, they benefit many more kinds of wildlife than just the oak moth! - Birds of course, and butterflies - the California Sister butterfly in particular. They create a whole ecosystem where they grow - The Las Pilitas nursery web site has a lot to say about them. They grow easily from seed - see this link for some propagation info.

Oaks of all sorts are just great!