I learned about the star shape inside cottonwood twigs from a Lakota story. The stars were not always in the sky. They originated in the earth, seeking roots from which they could be born. The sound of water drew them to the cottonwood roots (since this tree often thrives near water). They traveled upward into the trees, waiting for wind to snap the branches, releasing the stars into the sky. The story made me wonder if other trees have this star shape inside their twigs and branches, and what purpose does the star pattern inside the twigs serve (other than cosmological)?
In exploring winter twig keys and a story by Deb Mowry of the Montana Natural History Center, I learned that this five-pointed (also called five-angled) star shape is common in Populus (aspen, poplar, cottonwood) and Salix species (members of the willow family) but is also found in oaks (Quercus), and chestnut (Castanea). The pith inside a stem is made of parenchyma (large, thin-walled cells), which are often a different color than surrounding wood (xylem). The pith’s function is to transport and store nutrients. Pith is usually lighter when new, but darkens with time (as seen in images like these of cottonwood “stars”).
Mowry’s story notes the importance of cottonwood to the belief systems of Native American tribes: the Lakota, the Cheyenne, the Arapaho, and the Oglala Sioux. Pacific Northwest naturalist and poet Robert Michael Pyle’s essay, “The Plains Cottonwood” (American Horticulturist, August 1993, pp.39-42), describes an Arapaho version of the story of the stars that you told above: “They moved up through the roots and trunks of the cottonwoods to wait near the sky at the ends of the high branches. When the night spirit desired more stars, he asked the wind spirit to provide them. She then grew from a whisper to a gale. Many cottonwood twigs would break off, and each time they broke, they released stars from their nodes.” Cottonwood twigs sometimes snap off without the assistance of wind, a self-pruning phenomenon called cladoptosis. Pyle suggests looking for twigs that are neither too young nor too weathered if you want to observe the clearest stars: “The star is the darker heartwood contrasting with the paler sapwood and new growth.”
I am trying to help my neighbors select trees for their front garden. The trees will be in a parking strip that doesn’t have any structures near it or any overhead lines and it is on the north side of a fairly large 2-story house. We live in an old neighborhood with very large, grand trees. One tree I thought might be a contender, which is approved by the city (Portland, OR), is Cladastris kentukea. My only concern is that the seed pods might be messy. The neighbors themselves were thinking of aspen (nostalgic for them, as Coloradoans), but I didn’t think this was a good idea. What do you think?
I checked in a few places, and the main thing that might be disappointing is that in the Pacific Northwest, Cladrastis kentukea doesn’t flower reliably (although that solves the small trouble of seedpods, I guess!). Local tree expert Arthur Lee Jacobson says the following, in his book Trees of Seattle (2006):
“In nature this is an uncommon, even endangered species. It has been recorded to 87′ x 23′ x 96′ wide, and has reliable bright yellow or even yellow-orange fall color. Its heartwood is also deep yellow. Uncommon in Seattle, Yellowwoods are unreliable as flowering trees: their white flowers appear full force in some Junes, but are absent or weak in most years. They have no other faults except a branching habit prone to breaking up; careful pruning can help with this.”
(The Seattle-dwelling specimens of this tree which Jacobson lists are between 23-60 feet tall by 4 to 8 feet wide)
Below are links to information and images, from Oregon State University. This tree looks glorious when it flowers! Provided the spot is well-drained, and has no history of verticillium, to which Cladrastis is susceptible (see the link from SelecTree below for details), it seems like a great choice.
OSU
SelecTree
As an argument against aspen (Populus species, usually P. tremuloides in our area), Arthur Lee Jacobson mentions that they tend to sucker from the roots. The SelecTree site mentions twig and dry fruit litter, high allergen count, and numerous pest and disease problems.
When a cottonwood tree is cut down, does the stump die, or does it send out shoots that grow into more trees?
And, if a cottonwood tree located on a hillside is cut down, what is the risk of erosion?
As it turns out, some poplars and cottonwoods sucker from the roots and some do not. Determining what kind of cottonwood you have is the key to answering this question.
Identifying tree varieties can be tricky. The best way to get a positive ID is to take a sample to the Hyde Herbarium at the Center for Urban Horticulture (near the University of Washington). It is definitely worth a visit, as it is the only herbarium on the West Coast that serves the public.
Hours, driving directions, how to collect specimens, etc. are on the Hyde Herbarium page.
As for your second question, here is what the Washington State Department of Ecology’s Vegetation Management: A Guide for Puget Sound Bluff Property Owners has to say (p.25):
Given the importance of tree cover on potentially unstable slopes and the advisability of retaining them for erosion control purposes, a landowner should explore alternative options to tree removal or topping…[if a tree must be cut] stumps and root systems should be left undisturbed…[to reduce the risk of erosion].
A companion website from the Washington State Dept. of Ecology contains a great list of groundcovers, shrubs and trees that will help keep your slope intact if you decide to remove the cottonwood. The website includes a Plant Selection
guide.
Cottonwood and the River of Time by Reinhard Stettler explores an unlikely topic, cottonwood trees and their kin including poplars and aspens. A retired University of Washington professor of forestry, the author writes an engaging natural history beginning with a single tree, an old matriarch near the Snoqualmie River. While eventually global in scope, many of the examples continue to be set in the Pacific Northwest.
While many of the titles from the middle chapters may look a bit dull, e.g., “Natural Hybridization” and “Adaptation and Its Limits”, the writing is quite engaging and aimed at a general audience. The book concludes with cultural history of poplars–the importance of poplars in agriculture, forestry, and landscapes.
Excerpted from the Fall 2011 Arboretum Bulletin.
