Green Wednesday: Tackling Invasives & Woodpecker Wonders
By Tom Hixson, UC Master Gardener of Napa County / By Kathleen Scavone, Environmental Contributor
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Every Wednesday, Napa Valley Features includes posts from environmental voices and the UC Master Gardeners of Napa County, who share research-based horticultural advice. Together, these contributors provide valuable insights into sustainable gardening practices and climate-related topics relevant to our region.
"Trees of Heaven Are Not So Divine" by Tom Hixson, UC Master Gardener of Napa County: This article explores the invasive "tree of heaven" (Ailanthus altissima), detailing its aggressive growth, ecological impact and practical tips for managing its spread in Napa Valley landscapes.
"The Call of the Pileated Woodpecker" by Kathleen Scavone, Environmental Contributor: A celebration of the vibrant pileated woodpecker and its role in Napa Valley’s oak woodlands, encouraging appreciation and conservation of these lively forest inhabitants.
Trees of Heaven Are Not So Divine
By Tom Hixson
NAPA VALLEY, Calif. — Most Napa Valley residents recognize the plant known as “tree of heaven” when they see it sprouting wild in fields, taking over their gardens or defiantly establishing itself in sidewalk cracks. But despite its purported celestial provenance, this tree poses a significant threat to our landscapes and to agriculture.
Tree of heaven (Ailanthus altissima) is a medium-sized tree first exported from China to Europe in the mid-18th century and to the eastern United States in the 1780s. It was later introduced to California during the gold rush by Chinese miners who believed it had medicinal properties. But initial enthusiasm for the tree was based mostly on its ability to flourish virtually anywhere, regardless of drought, extreme heat or excess rainfall.
This tree never relaxes its efforts to spread.
Because it grows up to 90 feet so quickly and can easily be pruned into a handsome tree, it promised to become an attractive addition to landscape plantings. Appreciation for this tree declined, however, once gardeners became aware of its invasive nature and its foul odor, sometimes described as akin to rotting peanut butter.
Despite these drawbacks, tree of heaven was used extensively as a street tree during much of the 19th century, and it achieved top billing in Betty Smith’s 1943 novel “A Tree Grows in Brooklyn.” It has proliferated throughout the United States ever since.
In addition to having an unpleasant scent and aggressive growth habit, tree of heaven is the preferred host plant of several harmful insects, including the dreaded spotted lanternfly (Lycorma delicatula). This large plant-hopper feeds on — and largely destroys — more than 100 different plant species, including grapes, stone fruits and hardwoods.
Currently the spotted lanternfly has been identified in 18 states on the East Coast. It has the potential to spread rapidly, leaving severe damage in its wake. Tree of heaven is also the preferred host plant for another exotic and destructive pest, the brown marmorated stink bug, already found in much of California.
If you’ve ever gardened near an established tree of heaven, you will understand why its invasiveness is so concerning. It drops tens of thousands of its devilish seeds, which are carried in samaras, 1- to 2-inch pods cleverly engineered for maximum dispersal. On a windy day, the samaras scatter widely, then bed down for the winter under fallen leaves. In the spring, they are resurrected, sending vigorous new shoots to the surface.
Fortunately, at this early stage the seedlings can be easily vanquished by pulling them up by the roots. If not eradicated in the first few months, however, the vigorous young plants will develop tenacious root systems and become more difficult to remove. The entire root system must be dug up, or the plant will return in no time. It’s easier to uproot when the soil is damp.
In addition to having an unpleasant scent and aggressive growth habit, tree of heaven is the preferred host plant of several harmful insects.
What can you do to limit the spread of tree of heaven? First, learn to identify it. Its crushed leaves emit a strong and disagreeable odor, and by late summer its trademark seed-pod clusters appear.
Besides germinating from seed, the mature tree can reproduce through runners. Seedlings from runners can appear up to 30 feet away from the parent tree and need to be dug up and removed. Regularly removing these runner shoots will eventually discourage new growth, but the gardener must remain vigilant. This tree never relaxes its efforts to spread.
The most important thing you can do to manage this tree (besides removing the adult altogether, which is not always feasible) is to remove the samaras when they drop in the fall. A simple vacuum attachment to a leaf blower does an excellent job of picking them up.
Don’t put these seeds in a municipal compost bin. They will flourish elsewhere unless killed by rigorous hot composting. Instead, place them in a bag, seal it and send it to the landfill. It’s worth the effort to collect the samaras in the fall as you’ll greatly minimize sprouts the following spring.
California Master Gardeners are collaborating on a program to identify tree of heaven throughout the state with the goal of reducing its presence. Three hundred Master Gardeners have been trained to identify this tree and report its location, age and size. Researchers and public-works officials use this data to generate maps and prioritize trees for removal, but it will take years for this massive undertaking to have an impact.
Given that awareness of the problem is a key part of managing it, we home gardeners can do our part by teaching ourselves to identify tree of heaven. Then we can utilize available techniques to control its spread in our own neighborhoods.
Library Talk: Join UC Master Gardeners of Napa County for a Napa Library talk on “Growing Peppers” on Thursday, Jan. 2, from 7 to 8 p.m. via Zoom. Let’s parlez peppers — hot, sweet and mild. Learn the basics of starting peppers from seed, plus growing tips and usage ideas for your eventual harvest. Click here to register!
Help Desk: The Master Gardener Help Desk is available to answer your garden questions on Mondays and Fridays from 10 a.m. until 1 p.m. at the University of California Cooperative Extension Office, 1710 Soscol Ave., Suite 4, Napa. Or send your questions to mastergardeners@countyofnapa.org. Include your name, address, phone number and a brief description. For best results attach a photo.
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Tom Hixson is a UC Master Gardener of Napa County.
The Call of the Pileated Woodpecker
By Kathleen Scavone
NAPA VALLEY, Calif. — The clear call of a pileated woodpecker caught my attention recently in the luminous oak woods near the border of Lake and Napa County. The sound is distinct with a high, resonant series that is shrilly repeated across the forest by another pileated woodpecker. Next, I heard the thrum of deep drumming on the tree trunk loud and rich. That never ceases to thrill me! They seem energized and exuberant. As I snuck up on one bird and, miraculously, did not frighten it away, I understood that the woodpecker's lunch was more important than my proximity. This was turning out to be an A-plus day!
Oak woodlands, according to the beautiful book by Kate Marianchild, “Secrets of the Oak Woodlands: Plants and Animals Among California's Oaks,” explains that this ecosystem supports more species than any others, since it plays host to reptiles, insects, fungi, mammals and, of course, birds such as the pileated woodpecker. California is host to about 18 oak species, which have figured widely across time in the state's cultural history as well as the natural history of the state, enhancing the native plant populations of lichens and fungi, as well as an understory of wild rose, poison oak and numerous grass and avian species, including various woodpeckers. The complexities of nature's systems are like doors of mystery opening before us.
The word “pileated” in the woodpecker's name is derived from the Latin pileatus and means “capped,” according to Wikipedia. Measuring 16 to 19 inches long, this outsized species is the largest woodpecker breed living in North America. Its impressive bill is the length of its head. The head is crested with a bright red mohawk, while the remainder of the bird is colored mostly black, along with snazzy black and white throat stripes. EBird, managed by the Cornell Lab of Ornithology, contains many magnificent photos of pileated woodpeckers, and is loaded with information on the species and how to support these birds.
This outsized species, the largest woodpecker in North America, dazzles with its bright red crest and striking black-and-white stripes.
For example, you may want to think about keeping a tree snag on your property since they attract woodpeckers of all sorts, along with lovely nuthatches. The Napa Valley is host to not only pileated woodpeckers but also acorn woodpeckers, Lewis's woodpecker, various sapsuckers, Nuttall's, hairy and downy woodpeckers, and northern flickers, which are also in the woodpecker family. You may have heard or seen these birds in the parks, such as Bothe-Napa Valley State Park, Robert Louis Stevenson State Park or one of the many beautiful Napa Land Trust sites.
Did you know that a pair of pileated woodpeckers will remain together on its claimed terrain throughout the year? These vociferous birds dine on ants, termites and various insect larvae using their extra-strong bills as hammers and elongated tongues to locate their grub. All the foods making up their diet is available to them in conifer, hardwood and mixed forests.
Take a wander in the woods and get an intimate look at woodpeckers. They're a delightful avian species, and although not rare, are always a treat to behold. Living in deciduous forests across America, they will stop you in your tracks when you hear their call. It's not surprising that, according to Wikipedia, Walter Lantz based his Woody Woodpecker cartoon on the pileated woodpecker!
If today's story captured your interest, explore these related articles:
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Birdwatching in Napa County Reveals Avian Wonders and Conservation Champions
Calistoga's Old Faithful Geyser: From Tourist Trap to Natural Wonder
Kathleen Scavone, M.A., retired educator, is a potter, freelance writer and author of “Anderson Marsh State Historic Park: A Walking History, Prehistory, Flora, and Fauna Tour of a California State Park,” "People of the Water" and “Native Americans of Lake County.” She loves hiking, travel, photography and creating her single panel cartoon called Rupert. She can be reached through her website: www.KathleenScavone.com.
My dad planted this tree in our backyard in the 60's. I hated the smell, like rotting rubber to me. He soon took it out, so I never got to see the invasive quality.
Thank you for tackling the Tree of Heaven…something that I am seeing in my neighborhood more and more! was about to propose an article on my personal experience with French Broom… but more recently with my concern for growing strands of arundo in the Napa River, but very close to the Silverado Trail.