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Too Much of a Good Thing?

Recently we began a series of articles exploring the Inland Northwest’s common tree species. In 2018 we highlighted western redcedar and last fall we looked at western larch, two highly regarded species promoted by forest managers.

We now continue our series by taking on grand fir, a tree that, depending on who you talk to, has many wonderful characteristics or is considered to be a disease prone, disrespectful weed.

The good

When considering the positive aspects of grand fir, one is hard pressed to think it could cause any problems.

True to its name, grand fir (Abies grandis in Latin, meaning to rise, grand) is the tallest true fir species. In fact, Idaho’s tallest grand fir, found near the North Fork of the Clearwater River, measures 181 feet tall and 70” DBH. Truly a grand tree!  Idaho’s champion Douglas-fir is noticeably taller, but, then again, it is not a true fir. Causing some confusion, grand fir is also commonly called white fir (because its wood is very light colored) even though true white fir (Abies concolor) grows naturally further south in the Cascade and Rocky Mountain ranges.

Not only does grand fir grow tall, but it does so rapidly. It also grows well even in fairly dense stands, allowing it to produce high yields. In fact, according to Silvics of Forest Trees of the United States, it is second only to white pine among species with the highest yield potential.

In addition to fast growth, grand fir has other enviable characteristics. One of the most significant is the seed’s ability to germinate well on both bare soils and the forest floor. Deep initial root penetration then protects the seedlings from dry soil surfaces, giving it more drought resistance. Once established, it can survive and grow well in moderate shade. Only cedar and hemlock are rated higher in shade tolerance. If grand fir happens to become established in a stand where it can’t get enough light to grow, no problem, it can withstand suppression for a century or more and still respond well when released by an open canopy.

In addition to its many favorable botanical characteristics, grand fir offers up valuable forest products. In our region, most of the revenue comes from sales to local mills where it is commonly made into hem-fir lumber, a mixture of true fir and western hemlock that is well suited for general-purpose framing. But because it is not quite as strong or decay resistant as Douglas-fir and western larch, it often brings a slightly lower price. Grand fir’s shape, dark green foliage, needle retention, and wonderful smell make it an ideal Christmas tree. It is also popular as an essential oil. Essence of grand fir is said to “promote well-being and the sensation of deeper breathing.”  Indeed, if you have forest land in Bonner of Boundary County don’t be surprised if someone asks to collect some of your fresh grand fir slash to process into essential oils.

Throughout history, grand fir had many alternative uses including medicinal tea for colds, a salve for minor wounds, and incense to ward off illness. It has even been used to make baby powder, deodorant, and a concoction to prevent balding.

Wow, this tree does everything from bringing in money to preventing baldness! That’s enough to make grand fir sound like a fairly respectable tree. How could it cause angst in anyone? Well, since space for this article is limited, let’s just outline the most significant reasons.

The not so good

Grand fir’s main problem is an overabundance. Since it is vulnerable to wildfire, historically uncontrolled fires effectively limited grand fir’s range and easily kept its numbers in check. But more than a century of fire suppression has, regrettably, given grand fir plenty of opportunity to expand.

At the same time, periodic selective harvesting became popular which resulted in diseases becoming more widespread, especially root disease.  These events opened the forest canopy gradually creating ideal conditions (i.e. just enough light and the precise seed bed) to favor grand fir establishment over other species.

Grand fir’s fast growth and shade tolerance then allowed it to steal growing space from other trees. To add more fuel to the fire (pun intended), weak, immature stands are highly susceptible to snow damage so thickets of stressed and damaged trees quickly developed into a forest prone to wildfire.

To complicate things further, grand fir is a rather site sensitive species, making it less resilient to unusual climate swings. Furthermore, grand fir’s expansion has taken it to marginal sites where it performs poorly. Hard pan soils with a fluctuating water table provide one good example.

Because of this constellation of factors, native insects and diseases that would normally exist within the population in low numbers now have an opportunity to cause severe loss. In our local forests, fir engraver beetle provides one of the best examples. (Damage from this insect can be very apparent because when the insect kills the tree, it often turns bright red. Unfortunately, the color often does not show until the year after attack, when the beetles are already gone. )  This beetle got a really big boost after the severe drought years of 2014 and 2015 and, since it is not uncommon for high levels of beetle activity to continue several years after such an event, we still see the impacts even after a return to healthier precipitation levels.

Grand fir is also very susceptible to tussock moth, spruce budworm, and balsam woolly adelgid which take a significant toll. When damaged by logging, or frost cracks, heart rot may set in allowing the introduction of Indian paint fungus.

Once again, we could go on but the point has been made. Grand fir is a native tree with desirable characteristics that is causing some serious problems. So what can we do?

Management considerations

Here are a few general principles to keep in mind when working with grand fir. Of course, ownership objectives and forest condition ultimately drives specific actions.

  • All cutting prescriptions need to consider their potential to promote grand fir and then strive to favor the development of other species wherever possible.
  • Addressing challenges in stands where grand fir has taken a firm hold can be expensive and time consuming and will likely require repeated entries.
  • Commercial stands with grand fir in them can easily be over-thinned thereby opening the forest too much (with good intentions) and exposing the stand to increased wind damage, potentially accelerating the spread of root disease and favoring conditions for undesirable understory development.
  • In areas with root disease or many declining trees, species conversion may be the best option, i.e. cutting all of the vulnerable species while creating planting areas for seral tree species.
  • Pre-commercial thinning is a useful tool to improve overcrowded stands of younger grand fir and shift species mix in favor of more desirable trees; however, thinning pure grand fir stands where root disease is prevalent can actually increases the rate of spread for this fungus. It is often best to avoid thinning altogether in very active root disease pockets.
  • Check in with a consulting forester or your local Idaho Department of Lands Service Forester to see what management options best suit your stand.

-Steve Bloedel, ACF, Certified Forester

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