It’s Earth Day today, and we’d like to talk about the importance of Eucalyptus trees. Surprisingly, even some people who identify as environmentalists have no idea of the far-reaching value of these trees in our environment.
San Francisco has a lot of eucalyptus trees, mainly in its parks. According to a 2007 USDA report on San Francisco’s urban forest, this species accounts for over 16% of the the total of 669,000 trees in the city. This more than any other kind of tree. It’s a sturdy, fast-growing, graceful tree that grows where others will not – in areas of high wind.
(Monterey pine and Monterey Cypress are next, together accounting for about 12%. But unlike the eucalyptus trees, which are healthy and long-lived, many of these trees are nearing the end of their lives and have infections of bark beetles and pitch pine canker.)
As we enter a world of increasing climate change, we’re starting to understand the value of carbon storage. Trees capture carbon dioxide from the atmosphere, and store it in their wood, roots and leaves – and in the soil beneath them. The actual amount stored is proportional to the dry weight of the wood and organic matter. Eucalyptus is particularly good at sequestering carbon.
- Its wood is very dense, which means it holds more carbon for each cubic inch of wood;
- It grows fast, which means it take up carbon quickly;
- It grows large, which again means it stores more, in the trunk and branches and its root system.
- It lives a long time, around 400-500 years in the kind of wet conditions we have in San Francisco, which means it will not be giving back the carbon any time soon.
According to the Report, “Of all the species sampled, blue gum eucalyptus stores
and sequesters the most carbon (approximately 24.4% of the total carbon stored and
16.3% of all sequestered carbon).”
In places like Sutro Forest, where it grows in association with acacia trees – a nitrogen-fixing species – it’s even better at storing carbon. The carbon gets stored in the trees and the soil. Sutro Forest is an excellent carbon sink.
HABITAT FOR WILDLIFE
Eucalyptus has nectar-rich winter-blooming flowers. It’s the largest flowering plant in the world. In the Bay Area, it flowers when few other trees or plants are in bloom, and its flowers are rich in nectar. It provides a food source to insects and the birds that feed on them, as well as directly to nectar-feeding birds.
(And if you’ve heard the urban legend about eucalyptus resin killing birds – it’s not true.)
- Eucalyptus trees provide nest sites for a whole variety of birds. As the trees mature, cavities form or are excavated by woodpeckers. These form nest sites not just for woodpeckers, but Western Bluebirds and other cavity-nesters. The crooks of the branches provide nesting spaces for Great Horned Owls and for Red-tailed Hawks.
- Where ivy or other vines are allowed to grow on eucalyptus trunks, they provide additional nest sites – as well as excellent cover for little birds, bats, and small animals to hide from predators like hawks.
In areas like parks – or Sutro Forest – where the leaf litter is allowed to accumulate under the trees, it provides an excellent habitat for small reptiles like salamanders. The damp environment is good for animals like banana slugs, which have been seen in the forest.
POLLUTION AND SOUND CONTROL
Like all trees and bushes, eucalyptus helps control pollution, especially particulate pollution. The particles are trapped on the leaves, and washed to the ground when it rains – thus staying out of our lungs. Barriers of trees and dense vegetation also help absorb the sounds of urban life.
The Report calculates an “Importance Value” based on the percentage of trees plus the percentage leaf area. For eucalyptus, that is calculated at around 27%. (Monterey Pine is higher, at 31%, but as we said – there are issues with the health of that species.)
SLOWING WATER RUNOFF
San Francisco is working hard to slow water run-off, to keep rain water out of our sewer system and let it soak into the ground. They’re encouraging people to use build sidewalk gardens and use permeable paving so water can get through to the ground rather than run off.
Eucalyptus is excellent at slowing water. It moves a lot of water, sucking it in through the roots, and transpiring it through its leaves. The leaf litter and plants that grow below it also help in trapping wand slowing water. In San Francisco, they help enormously in slowing run-off; you can see the obvious difference after a rain-storm between the water running off Twin Peaks Boulevard in a river, and the relatively small amounts running off Mount Sutro.
NATIVISTS DESPISE EUCALYPTUS
As we’ve been reaching out to let people know about the threat to Sutro Forest, we’ve been encountering some people who despise eucalyptus. We’re not talking of developers, who don’t actually hate trees, only obstacles of whatever species or nature. We mean people who identify as environmentalists – as we do, too. But they have focused on Native Plants, and fail to recognize the importance of eucalyptus in our environment.
We urge UCSF, the Sutro Stewards, and SFRPD to recognize the urban environment we live in, and the unique value of eucalyptus in our city. No other tree is as useful from an environmental standpoint. It’s time to stop attacking these trees and to start recognizing how much they’re doing for us.
San Francisco had, in 2007, only 12% canopy cover – less than almost every city in the report except Jersey City, NJ. Our city cannot spare its majestic and valuable eucalyptus trees.