As spring is transitioning into summer
and the Salmonberries (Rubus spectabilis)
ripen, the warm breeze has started to carry off the fluffy down of Cottonwood
trees (Populus balsamifera ssp. trichocarpa). Grassy meadows thickly layered with cottonwood
fluff share a likeness to December’s ephemeral snow storms, but in many ways, this
“snow” represents winter’s antithesis.
The days are approaching their longest and the trees are nearing their
peak of new growth.
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| On this piece of Cottonwood bark, the newest growth has a translucent quality. |
All tree growth is a result of cell
division (mitosis) and the cambium cell layer is responsible for enlarging the
girth of a tree trunk. As cambium
divides, the cells on the inside eventually harden into wood, and the cells on
the outside turn into bark. Timing is
critical for successfully harvesting cambium.
You want to collect the cambium when growth rates are fast enough that
there is a thick layer of new tissue that hasn’t yet turned into wood. These new tissues also serve as the blood
vessels of the tree carrying water, sugars, and secondary metabolites like
tannins up and down the tree. Life
history events such as the production of new leaves and needles, flowers,
pollen, or seeds, put special demands on the tree which require the mobilization
of special resources through the cambium.
Theoretically, if you were able to hone in your harvest timing to
coincide with moments when the cambium is full of sugars and relatively free of
bitter tannins, you could maximize your cambium's culinary potential. See Megan Dilbone's master's thesis on the ethnobotany of Lodgepole Pine (Pinus contorta) cambium for more details. Easily observable phenological clues, such as
the release of tree pollen (in pines), can be very useful in identifying the proper
harvest time for cambium and are part of the corpus of traditional knowledge
held by the Native Americans that enjoyed eating cambium. In the case of Red Alder (Alnus rubra), even the position of the
tide was considered by the Salish (best to harvest at high tide).
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| Cottonwood cambium scraped and ready to eat. |
Here in the Pacific Northwest, Native
Americans utilized an incredible diversity of trees for edible cambium
including Western Hemlock (Tsuga
heterophylla), Sitka Spruce (Picea
sitchensis), Bigleaf Maple (Acer
macrophyllum), Red Alder, Lodgepole Pine, Quaking Aspen (Populus
tremuloides), and Black Cottonwood. The
air alighting with Cottonwood down is a pretty dramatic phenological event, so
I set out to taste test some “cotton-camby” (Cottonwood cambium). I selected a Cottonwood tree that was about 1
foot in diameter and sliced a rectangle into the bark with my pocket
knife. Then I carefully pried the bark
away from the tree. This time of the
year, the bark is relatively easy to remove because the sap is flowing
strongly. I then scraped off the soft
and juicy new tissue from the inside of the bark and ate it fresh. The flavor of the cambium was mildly sweet
with a hint of cucumber and only a touch of bitterness—by far the best cambium
I have tried so far.