Dieback in North Idaho’s Fir Trees Explained

Rampant dieback is evident in area trees, but why?

This year, many of us noticed conifer dieback —especially affecting fir trees—on our properties and in our surrounding forests. The flaring out (or reddening) of so many trees is alarming to those of us familiar with bark beetle infestations elsewhere, including those decimating entire hillsides in Montana and Colorado. Are our tree stands doomed, too?

The thing is, bark beetles aren’t to blame for what we’re experiencing here; they’re just finishing off a job begun by other factors. The fir dieback we are now seeing actually has its roots in a century’s worth of logging, fire suppression, and the introduction of pathogens like white pine blister rust. This all contributes to more grand fir, Douglas fir, and subalpine fir than North Idaho has traditionally supported.

Next, the hotter, drier summers of recent years have stressed out our trees, leaving them more susceptible to diseases and pests. Thus, pathogens that healthy trees can easily fend off are now flourishing amidst weakened “immune systems.”

One such problem is the myriad native fungi that lead to root rot. Doug fir, grand fir, and subalpine fir are the species most susceptible to root diseases, and these diseases alone—even without the beetles—are leading to massive dieback.

Since the fungi responsible for root rot live in the soil and remain onsite through generations of trees, this problem isn’t going away anytime soon. However, even in the face of drought, there are things a landowner can do to diminish the threat of dieback. The first step is to thin the forest so trees aren’t competing for water and nutrients. Twelve to fifteen feet between saplings (more for larger trees) is a good rule of thumb. The second step is to ensure forest diversity, including a majority of trees tolerant of root diseases. These include (in descending order): ponderosa, Western larch, Western red cedar, lodgepole pine, Western white pine, Western hemlock, and Engelmann spruce.

Fir trees sometimes struggle and survive at the brink of dieback brought on by drought and root diseases, but opportunistic beetles exist to finish off the job. In North Idaho, we have over 100 species of bark beetle, each specializing in different conifers and sometimes even different parts of specific conifers. These beetles are a natural part of our forest, but they are flourishing right now due to the aforementioned factors of drought, overcrowding, fir population imbalances, and root rot.

If you notice fir dieback (or other struggling trees) on your property, give us a call. We can provide an assessment of your trees and forest and how best to tackle the domino effect that runs from drought to dying trees.

For more information on area tree diseases, check out “A Field Guide to Diseases & Insect Pests of Northern & Central Rocky Mountain Conifers.” To learn more about root diseases in particular, visit “Root Diseases in Coniferous Forests of the Inland West.”

 

Root Problems: The Most Difficult Hazard to Detect

Root problems might be simmering under the forest floor, waiting to topple your trees…

Root problems are the most difficult hazards to detect because most of the problem is underground and out of sight. People often have to wait for the visible portion of the tree to be affected before determining that there are root problems. Above-ground signs of root problems might include dieback, discolored needles or leaves, leaning with recent root exposure, as well as soil heaving, conks, or sap flow near the base of the tree. Also, failing trees nearby could indicate that the still-thriving trees might have a root problem.

Roots are essential to the structural support of your trees. They literally hold your tree to the earth. Thus, when root systems begin to fail, trees become a hazard to nearby people and property. Root problems may lead to blow-down in windstorms or tipping over without warning under the weight of leaves in the summer. Root problems are often silent but carry deadly consequences.

root problems

Decay fungi often indicate that a root problem is present.

There are two types of root problems: physical and biological. Decay fungi often cause biological root problems. This becomes evident when conks appear near a tree’s roots and in nearby decayed stumps. However, only about half of the trees infected with root rot might show symptoms at any one time. In this region, grand fir and Douglas fir are particularly prone to laminated root rot. Idaho Department of Lands provides an excellent and informative explanation of laminated root rot.

Physical root problems are often human-caused. They include severed, loosened, cracked, broken and exposed roots. Construction or paving near a tree, driving vehicles over roots (soil compaction), and raising or lowering the soil level near a tree can all cause physical root problems. In attempting to diagnose a failing tree, we may ask you questions about recent activity on your property. If you’ve just constructed an addition to your house or have rerouted your driveway or plumbing, that might be the problem.

One final physical root problem that is not human-caused is the girdling root. These roots grow around or across the trunk or other roots on the tree. As the tree grows, girdling roots may begin to choke the tree, reducing its ability to take in water and nutrients. Symptoms are similar to those you might see in drought, including early fall color and dieback.

Of all of these issues, the symptom you should be most concerned about is a tree demonstrating an increased lean with cracking or mounding soil at the base. This is a serious hazard and should be dealt with immediately, before it falls on its own…because it will soon fall. Even if you only suspect root problems in one of your struggling trees, give us a call. We’re happy to provide an assessment and free estimate.

For more information about root diseases, go to the Forest and Shade Tree Pathology website. And to learn more about your potential hazard trees, don’t hesitate to contact us.

Cankers: An Easy to Spot Hazard

Cankers are often quite visible, but cause and treatment aren’t always straightforward…

Cankers tend to be prominent. If your tree has a potentially hazardous canker, it’s hard to miss. Think of the tree version of a large, open wound or deformity, and you’ve got the visual idea of cankers. They may be ugly, but are they a problem? Maybe yes, maybe no. And maybe not quite yet.

Baumkrebs-Birke

An older callused canker on a paper birch. Photo courtesy Markus Hagenlocher via Wikimedia Commons.

Visually speaking, cankers are places on the trunk or branch of a tree where the bark is sunken or missing. They can lead to hazardous situations, creating weak spots where breakage can occur. Of most concern are cankers that affect more than 120 degrees of the tree’s circumference or cankers connected to other tree defects (e.g., cracks, weak branch unions, or cavities). Also of concern are cankers that are either directly facing or opposing prevailing winds.

Otkrytyj_smol’anoj_rak_na_jeli

Note the callus formed on the canker on this spruce tree. Photo courtesy Сыроежкин via Wikimedia Commons.

 

 

Cankers are typically caused by bark-inhabiting pathogens (usually fungal or bacterial), but sunscald and frost can also cause cankers by killing patches of bark. And while a wound on a tree (an improperly cut branch or a damaged place on the trunk) won’t directly lead to a canker, it can be the entry point for pathogens that will.

Cankers can either be annual or perennial. The annual ones are handled in a single year by a healthy tree, which grows a callus over the affected area. A perennial canker returns year after year, growing slightly bigger in the process. The pathogens attack the callus each year, meaning the tree has to start over again. These cankers often have the look of a target on the face of a tree, exhibiting concentric circles. Though these cankers may be visually unappealing, they are slow-growing, and you may be able to enjoy your affected tree for years to come.

What you really need to be concerned about is canker rot. This is when the canker is actually associated with fungi that is decaying wood inside the trunk of the tree. Thus, you have the combined issue of poor internal structure (from the rot inside the tree) and dead bark and tissues on the outside of the tree. Trees exhibiting canker rot are very hazardous and should be dealt with immediately.

Cankers come in all shapes, sizes, and can be from scores of different pathogens. Often, we can’t pinpoint how exactly the canker came about, but we can assess your tree and let you know if the canker is simply an eyesore or a true hazard.

For more information on cankers, the Forest and Shade Tree Pathology website is absolutely the best place to go…and it will make your head spin with all the scientific information they have to share. For an overview, go to their Cankers page, and to learn about specific diseases, go to Cankers on Parade.