Monday, June 11, 2012

Cotton-Camby (Cottonwood Cambium)

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.

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).

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.

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  3. Black bears are fond of douglas fir cambium in young fast growing trees (typically in the 15 year old range). At one time I was a forester working to prevent this behavior (unsuccessfully, for the most part). They go after it in late May-early June, before the berries are ripe. I tried some of it myself and found it to be very sweet. Certainly worth eating in a pinch, and by no means a chore otherwise. Porcupines also utilize this food, usually higher up in the tree.

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