The consumption of tree bark is an ancient practice, but its safety and nutritional value depend entirely on the specific species and the part of the bark consumed. Botanically, bark includes all tissue layers outside the vascular cambium, which is the living growth layer. This protective outer layer shields the tree from physical damage, weather, and pathogens. To safely consume bark and derive benefit, one must differentiate between the dead, indigestible outer layer and the thin, nutrient-rich layer beneath it.
The Edible Layer: Cambium and Nutritional Value
The edible portion of the bark is the inner layer, which includes the phloem and the vascular cambium. The vascular cambium is a thin, living layer of cells situated directly between the outer bark and the wood. This tissue transports sugars and other nutrients throughout the tree by producing new wood inward and new inner bark (phloem) outward.
Because of its nutrient transport role, the inner bark is rich in stored carbohydrates, such as starches and simple sugars. This layer also contains various minerals, vitamins, and a significant amount of dietary fiber. While nutritional density is relatively low compared to processed foods, providing about 80 to 100 kilocalories per 100 grams, it serves as an energy source during scarcity.
The inner bark of certain species, including most Pines, Slippery Elm, Black Birch, and Maple, is considered edible. It is often harvested in the spring when high sap flow makes the cambium soft and slightly sweet. The flavor and texture vary widely, ranging from a starchy consistency to a taste that may be mildly sweet or sometimes bitter and resinous.
Toxicity, Indigestibility, and Poisonous Species
While the inner layer offers some nutritional value, the majority of the bark structure is highly indigestible for humans. The outer bark, or rhytidome, is composed primarily of dead tissue containing high concentrations of cellulose and lignin. Since humans lack the cellulase enzyme needed to break down cellulose, these components pass through the digestive system without providing nutrition. Consuming large amounts of this fibrous material can cause severe digestive upset, mechanical irritation of the gut lining, or intestinal blockage.
Many tree species contain toxic compounds concentrated in the bark and sap that pose a significant health risk. For example, Wild Cherry contains cyanogenic glycosides, which the body metabolizes into hydrogen cyanide. Ingestion can lead to symptoms such as confusion, headaches, and diarrhea, and in larger doses, it can be fatal.
The Yew tree is another example, as its bark and other parts contain taxine alkaloids, which are highly cardiotoxic compounds. Even small amounts of toxic bark can result in severe cardiac effects, gastrointestinal distress, and central nervous system disruption. Furthermore, bark acts as a natural bio-indicator, absorbing pollutants like heavy metals and organic contaminants from the environment. Consuming bark harvested from urban or industrial areas risks ingesting these accumulated environmental toxins.
Contextualizing Consumption: Historical and Survival Uses
The consumption of inner bark was common in northern latitudes where growing seasons are short. Indigenous cultures, such as the Sami people of northern Europe and various Native American tribes, utilized inner pine bark as a regular staple food, not just an emergency ration. This practice provided necessary carbohydrates, fiber, and vitamin C, balancing their predominantly protein-rich diets.
To improve palatability and digestibility, harvested inner bark was processed. People often dried strips of cambium and ground them into a flour or meal. This meal could then be mixed with other ingredients to make bread or thicken soups and stews. Preparation methods sometimes included cooking the bark in earthen oven pits.
Certain tree barks have also been incorporated into traditional medicine for their therapeutic properties. Willow bark, for instance, contains salicin, a glycoside that the body converts into salicylic acid, known for its pain-relieving and anti-inflammatory effects. Similarly, Cinchona tree bark was historically used to extract quinine, an alkaloid that served as the first effective treatment for malaria.