Pilkington Creek lies behind the Santa Cruz Museum of Natural History building and continues roughly ⅛ mile (500 feet) down river ending at Seabright Beach. The land along Pilkington Creek is dotted with populations of oak and eucalyptus.

The indiginous Awaswas people lived in western Santa Cruz County, along the coast from slightly north of Davenport to Rio del Mar, and they used native oak trees extensively. Eucalyptus trees, in contrast, were introduced to California following the arrival of European settlers but are now as commonplace as the native oak throughout the area once inhabited by the Awaswas. Both trees are beneficial to the landscape in some way and both are strongly associated with the California coast.

At what point does a non-native plant become essential to an ecosystem, or in other words, native? Does it ever? Let’s take a look at the Awaswas’ relationship with the oak and the Europeans’ relationship with the eucalyptus, then you can decide.

Acorns: Not Just for Squirrels

During the 16th and 17th century, the native Awaswas peoples may have kneeled by Pilkington creek, harvesting plants that once grew along its edges. If you visit in autumn, be sure to look for acorns littering the ground.

Acorns were an important part of the Awaswas’ food supply. Don’t try to take a bite out of this nut though. The Awaswas had to spend days processing the acorns — first by cracking open their hard shells and pounding them into a paste with a mortar and pestle, then leaching the tannic acid from the acorn meal, possibly with water from a creek like this one. Then the meal was boiled in a basket with stones heated over a fire.

Food & Lodging in California’s Oaks

Today, California’s oaks provide nourishment for many types of wildlife. Bears, mule deer, insects, and about two dozen species of birds all thrive on a diet that includes acorns. One mule deer alone can eat more than 300 acorns per day — it’s no wonder the Awaswas and other tribes in the area enlisted the help of the whole tribe come harvest time!

Cavity-nesting birds such as barn owls and wood ducks live in hollows in oak trees and these voids provide a winter hideout and summer home for squirrels. The arboreal salamander also makes its home in these cavities. The hollowed out trunk of an oak provides the perfect spot for a beehive and the bark provides habitat for spiders and centipedes.

On the ground you may see slugs, snails, caterpillars, ants, and earwigs ooze, inch, scurry, and scuttle beneath the leaf litter at the oak’s base and nematodes (tiny roundworms) and earthworms crawl throughout the tree’s root system. Also found intertwined in the oak’s root system are the tiny filaments, or mycelium, of numerous types of fungus. Some of these fungi form symbiotic relationships with the trees they cohabitate with– in fact, this oak would likely not be able to thrive without its beneficial fungus companions!

The oak woodland is a vital habitat to many native species. Eucalyptus trees, in contrast, actually prevent many native species from living within their barren groves — except, that is, for the monarch butterfly.

The Introduction of Fast-Growing, Flammable Forests

Accompanying the critters on the ground are flower caps from the eucalyptus, similar to acorn caps but darker and rounder with a cross split on top. The tree’s narrow, pointed, bluish-gray leaves that crackle and crunch underfoot may also carpet the ground.

The eucalyptus was first introduced to California in 1853 as an ornamental tree, but by 1880 it was also planted for lumber, firewood, medicinal products, oil, and windbreaks. The gold rush resulted in a frenzy of construction around the San Francisco area and thus a need for lots of lumber, fast. During this time the redwood, coast live oak and scrub oak forests were drastically thinned. The eucalyptus, one of the fastest growing trees, appeared at first to be a good replacement. Unfortunately, the tree had several downsides.

One downside is that when a relatively young eucalyptus is harvested, the tree’s wood twists and cracks and it rots too quickly to be of much commercial value, unlike the higher quality timber of centuries-old virgin eucalyptus forests Europeans had encountered in Australia. Eucalyptus forests are also a fire hazard due to a highly flammable oil in the leaf litter. To make matters worse, the trees release a toxin into the soil that prevents native plants from growing in or near eucalyptus groves.

Another unforeseen downside to the eucalyptus is the tree’s unquenchable thirst. Eucalyptus trees can soak up a huge amount of water. In fact, stands of them can dry out nearby swamps and the global spread of eucalyptus trees has wreaked havoc on some native wetland communities.

Eucalyptus: Bad for Biodiversity but Good for Butterflies

Today the eucalyptus is perhaps best known for its importance as a monarch butterfly habitat. Every October through February, eucalyptus groves in Santa Cruz provide a resting place for thousands of these migrating butterflies. Natural Bridges State Park harbors most of the area’s monarchs, hosting migration festivals and leading tours of the park’s monarch sanctuary.

So, the question remains: Does the native oak belong but not the non-native eucalyptus? At first look, it does appear the eucalyptus is doing more harm than good and yet it now provides important habitat for the monarch butterfly.

What do you think?

If you’d like to try eating acorns, check out this fun article.

Diluted eucalyptus oil can also be consumed or used topically, but undiluted the oil can be toxic. For more information, check out SF Gate’s article here.

Take the Self-Guided Mobile Tour

This piece is part of a walking tour all about Pilkington Creek by the Santa Cruz Museum of Natural History. You can download the free mobile app with many tours of the Santa Cruz area and beyond.