The Edible Part: What is Cambium?
When discussing the consumption of tree bark, it is crucial to understand that only the inner layer, known as the cambium, is ever considered for consumption. This soft, moist, and often lightly sweet layer is the tree's growth tissue, containing the phloem and outer secondary xylem, which transport nutrients and water throughout the tree. The outer, rough bark is not edible for humans due to its high cellulose content, which our digestive system cannot break down, and it often contains bitter and indigestible compounds.
Foraging for cambium requires careful technique and identification. To harvest, a small, vertical strip of the inner bark is carefully scraped away without penetrating into the hard, inner wood. Harvesting too much can severely damage or kill the tree, making sustainable practices essential.
Nutritional Value of Inner Bark
While not a rich source of macronutrients, the cambium of certain trees offers some nutritional benefits, particularly in a survival scenario. The value varies significantly by species and season, with spring harvests generally having higher starch and sugar levels.
- Carbohydrates: The inner bark contains digestible starches and sugars that provide a modest energy source.
- Vitamins and Minerals: Pine bark, for instance, has been noted to be rich in vitamin C, helping to prevent scurvy in historical accounts. It also contains essential minerals like calcium and potassium.
- Fiber: Tree bark is an extremely high-fiber food, which can have both positive and negative digestive effects. While it aids in digestion and provides a sense of fullness, it can also lead to significant stomach discomfort and is difficult to digest in large quantities.
Safe vs. Toxic Tree Bark
Species identification is the single most important factor for safe bark foraging. Mistaking a toxic tree for an edible one can have severe, even fatal, consequences.
Edible Tree Bark
- Pines (most species): The inner bark of many pine varieties, especially the White Pine, is a well-known survival food. It is relatively easy to access and can be prepared in various ways.
- Birch: The inner bark of birch trees is edible and can be used to make flour for bread. Black and yellow birch also offer a distinctive wintergreen flavor.
- Slippery Elm: Valued for its soothing, mucilaginous properties, slippery elm bark is often used to treat sore throats and digestive issues.
- Aspen and Poplar: The inner bark of these trees is reported to be somewhat sweet and starchy.
- Shagbark Hickory: An exception, the outer bark of shagbark hickory is used to flavor syrups.
Toxic Tree Bark (To Be Avoided)
- Yew: All parts of the yew tree are highly poisonous and should be completely avoided.
- Ponderosa Pine: While many pines are safe, the bark and needles of the Ponderosa pine are considered toxic and should not be consumed.
- Oak: Oak bark contains high levels of tannins that can be toxic in high doses and is unsafe when used on broken skin.
- Buckthorns: Certain species, like alder buckthorn, have strong laxative effects and are not recommended for consumption.
Preparing Bark for Consumption
Raw bark is often bitter and tough, so preparation is key to making it palatable and more digestible. Here are some common methods:
- Frying: Thinly sliced strips of cambium can be fried in oil or animal fat until crispy, creating a jerky-like texture.
- Boiling: Slicing the inner bark into strips and boiling it can soften the texture, making it edible in soups and stews.
- Grinding into Flour: Dried bark can be ground into a fine powder and mixed with grain flour for baking bread or thickening dishes. Historically, this was a common method for extending grain supplies during famines.
- Making Tea: Some barks, like slippery elm, can be infused in hot water to create a soothing tea.
Comparison: Edible Bark vs. Standard Food
| Feature | Edible Inner Bark (Emergency Use) | Standard Food (Typical Diet) |
|---|---|---|
| Nutritional Density | Low; high in fiber, moderate carbs, some minerals and vitamins | High; diverse macro and micronutrients |
| Caloric Value | Modest; low caloric density compared to nutrient-rich foods | High; provides substantial energy for bodily function |
| Digestibility | Can be difficult; very fibrous, potential for gastrointestinal upset | Optimized for human digestion; minimal discomfort |
| Sourcing | Requires identification, foraging skill, potential tree damage | Readily available through stores or cultivation |
| Health Risks | High risk of poisoning if misidentified; risk of chemical contamination | Low risk of toxicity; subject to proper food safety handling |
| Palatability | Often bitter or bland; taste varies widely by species | Generally pleasant and appealing due to preparation |
Significant Health Risks and Precautions
Foraging for and consuming tree bark is not without serious risks, even for experienced individuals. The practice should be reserved for extreme survival situations only, and never as a dietary novelty.
- Misidentification is Catastrophic: The most severe risk is mistaking a toxic tree for an edible one, which can lead to poisoning. Some toxic species closely resemble their edible counterparts, making positive identification by an expert non-negotiable.
- Chemical Contamination: Trees in urban or polluted areas may absorb heavy metals and other toxins through their roots, which can be present in the bark. Pesticide or herbicide residue is also a concern.
- Digestive Issues: The high fiber and tannin content in many barks can cause significant stomach upset, diarrhea, or digestive tract irritation, particularly with prolonged use.
- Damage to Trees: Irresponsible harvesting, or girdling (removing a ring of bark around the circumference of the trunk), will kill a tree. Sustainable foraging, if necessary, should focus on fallen branches or careful, minimal vertical strips.
- Allergies and Interactions: Certain barks, like willow bark, contain compounds similar to aspirin and can cause allergic reactions or interact with blood-thinning medication.
Conclusion
While eating the inner bark of specific trees is a historically documented survival technique, it is neither safe nor advisable for general nutrition. The risks associated with misidentification, chemical contamination, and digestive distress far outweigh the limited nutritional benefits. Modern nutritional science confirms that a balanced diet of readily available foods is the safest and most effective way to meet your body's needs. Foraging for bark should only be considered a last resort in extreme emergencies, and only after positive identification by a seasoned expert. As a rule, unless you are in a genuine life-or-death situation and are completely certain of your tree identification, you should not consume tree bark. For comprehensive information on safe foraging practices, consulting reputable sources like the U.S. Forest Service is essential.
