The time of year is fast-approaching when many will begin bringing greenery inside to decorate for the season. There are many beautiful and fragrant choices, some last longer once harvested and some may be messier than others. The balsam fir, Abies balsamea, is a gorgeous, aromatic quintessential green conical Christmas tree option. However, almost all balsam firs produce resin-filled blisters covering their trunk, which periodically burst and the resin flows out, albeit slowly, but it can still be a sticky mess. But what purpose do those blisters serve?
These pitch filled cysts are ubiquitous on fir stems, with the exception of the very young saplings and very old boles. They can be as abundant as needles on the tree and are perfectly normal, in other words, they are not a symptom of possible disease or an indication of pests. Actually, scientists have theorized that the blisters can actually be part of a defense system against pests and disease.
Inside each blister is a fragrant, sticky, viscous liquid, not sap, mind you, but a resin referred to as “pitch”. Coniferous trees, of course, do produce sap as well, but it consists of sugars, hormones, enzymes and vitamins which serve as the tree’s nutrition, pitch serves an entirely different purpose. There are more complex chemical differences between sap and pitch but the simplest and easiest to picture description is this: no one makes delicious syrup from pitch (which is kind of like turpentine) and most would recognize pitch in its hardened, fossilized form when it is called “amber”.
All of the coniferous trees native to the U.S. produce these resins, although how and where production occurs varies by species. In pines, spruces and larches resin is found in tubular canals within wood tissues, while in firs, hemlocks and cedars pitch is present in the bark. The absence of resin ducts can help distinguish fir from spruce in processed wood products. In spite of their abundance and seeming ubiquity, there is still a fair amount of debate over the function of bark blisters (or other pitch containing structure). There is research which has classified the resin as a hydrocarbon compound produced as a byproduct, while other data suggests it is a useful secretion with mounting evidence supporting its function as protection from predation, pests and pathogens. The latter theory employs a simplistic mechanism: an insect attempts to burrow into bark to feed on sweet sap, but is instead embroiled in sticky resin and thus, foiled. Resins have highly antiseptic properties which most likely aid in prevention of decay and fungal intrusion.
Whatever the debate that remains regarding the resin’s function for the trees, humans have a long history of making use of these substances, specifically from the balsam trees. The refractive qualities of balsam resin led to its use as a mounting medium for microscope specimens and a cement for lenses and gun sights. For centuries these resins have been used as a fixative and glossing agent over oil paintings and to waterproof pottery. Many have started fires, sealed wounds and/or patched ripped gear on a backcountry camping trip. And historical uses also include dental procedures, cough syrups, head and stomach ache remedies and more. Of course, now there are synthetics for all of these purposes, but it is always interesting to learn where the original idea came from.
For more information or help with choosing trees for your landscape or even holiday decoration, contact your arborist and visit http://www.savatree.com/tree-service.html.