Guest Opinion: The Arastradero Preserve eucalyptus: great tree or giant weed? Guest Opinion: The Arastradero Preserve eucalyptus: great tree or giant weed? (May 05, 2004)

by Michael Closson and David Smernoff

There has been a good deal of coverage about the large eucalyptus tree that Acterra's staff killed, while acting as stewards of Palo Alto's Arastradero Preserve. Some context may help people make sense out of that controversial act.

Introducing non-native plants and animals to a region's ecosystem is an enormous and increasing problem in the United States -- and worldwide. These "invasive species" displace native species and sometimes dramatically alter natural processes. The National Invasive Species Council estimates that these unwelcome visitors cost our country $100 billion a year through the havoc they wreak on forests, grasslands, waterways, farms, parks and human health.

Some of the most infamous invasive plants -- kudzu, yellow star thistle, purple loosestrife, tamarisk, and Eurasian milfoil -- transform entire ecosystems, leading to the eradication of native plants and animals. Next to habitat fragmentation caused by human sprawl, the invasive-species invasion is the largest global threat to biodiversity. Many invasive plants are quite attractive. California's nurseries showcase an array of ornamental plants from around the globe: pampas grass, scarlet wisteria, Scotch broom, periwinkle, English ivy, ice plant and many other non-native plants. But some are highly invasive and just don't stay put in our gardens. Since they are not kept in check by indigenous insects, foraging animals and disease, over time these plants can dominate large areas.

Eucalyptus trees, often very attractive, are one of California's most invasive plants. They were introduced to the state in the 1850s as a fast-growing source of timber, fuel and shade -- 100 of the world's 600 eucalyptus species now grow here. None are native.

Within a few decades of their introduction, eucalyptus trees became a dominant feature in our coastal hills. Leland and Jane Stanford planted hundreds on the Stanford campus, which still is veiled from Palo Alto by a "eucalyptus curtain."

The ecological case against eucalyptus trees in California is strong:

1) Compared to native trees, eucalyptus provides little support for wildlife. California oaks support at least 100 times more insects, a primary food source of songbirds. Few native animals and birds find food or shelter in eucalyptus trees.

2) Chemicals in eucalyptus create toxic conditions in the soil and this plus their biomass of bark and leaves make it difficult for native plants to grow under their canopy.

3) Eucalyptus trees are hummingbird killers. Their sweet-scented flowers attract hummingbirds and other birds, such as the Ruby-crowned Kinglet, that on occasion are smothered by a tar-like pitch as they attempt to drink the nectar.

4) The extensive root systems of eucalyptus trees soak up large volumes of ground water, reducing the amount available to native plants and trees. Large stands have been known to dry up all-year streams, threatening local aquatic life.

5) Eucalyptus trees are extremely flammable. Called "gasoline trees" by firefighters, the combination of their combustible oil, copious litter and long strands of hanging bark make them into giant torches during a fire. The devastating blaze of 1991 in the Oakland hills was fueled by thousands of eucalyptus trees. In 1985, a eucalyptus-fueled fire flashed through portions of Arastradero Preserve destroying segments of the riparian canopy -- damage Acterra still is repairing.

In short, eucalyptus trees, especially in groves, are water-hogging, toxic and fire-prone "zones of ecological emptiness." They are a significant threat to biodiversity in California.

Despite the powerful indictment of eucalyptus trees in general, we acknowledge that reasonable people may disagree about the wisdom of girdling the large blue gum eucalyptus tree on the Arastradero Preserve. All we can say is we did what we thought was appropriate for the site.

Our charge is to restore the Preserve to a condition in which native flora and fauna can thrive. The great majority of our time is devoted to controlling fast-spreading weeds. After seven years of effort, we found that we could not successfully grow native plants and trees near the big eucalyptus. It was only then we decided to girdle it.

The tree will remain standing for many years, providing excellent perches for red-tailed hawks, great horned owls and other raptors. Over the years a lovely grove of native oaks, planted by our staff and volunteers, will grow around the dead eucalyptus tree, providing habitat and forage for a variety of native fauna.

We have no doubt that visitors to the preserve will come to love that oak-covered knoll, finding solitude and renewal there.

Michael Closson is executive director and David Smernoff is a board member of Acterra. They can be e-mailed at michaelc@Acterra.org and DavidS@Acterra.org.

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