Not to Kick You when You're Down, but another Incredible Tree Failure

I always hate seeing a tree fall, but sometimes there is no better way to learn about the way trees grow than from a post failure forensic investigation.  And while I know our last post was about a fantastic large tree failure, this was too good to pass up.

Our subject is a large mature willow oak that suffered a tremendous root plate failure.  This tree was growing in a known flood plain, and was one of the tallest trees on the block.

Notice the amount of standing water in hole left behind when the roots pulled from the soil.  Keeping the size of the root plate in mind, and the proximity to the camellia in the picture below, notice how the wet conditions allowed the roots to be pulled from underneath soil like a magician pulling the table cloth from a fully set table.

The only indication of decay at time of failure was a cavity along the lower trunk/root flare of the tree.

Now, here is a part of the tree we don't get to see often.  With the root flare up ended we can see the structure and arrangement of the structural root system, and associated decay.

The decay column moving upward in to the stem is a common occurrence in many tree species.  It is a result of the original tap root dying off and allowing a path for decay to move into the stem.  This is a process that can take years, if not decades.  In species that compartmentalize well it is just a peripheral event, but for poor compartmentalizers, it may the defining defect in their demise.

Good thing the Jeep was insured.

Anatomy of a Tree Failure

All trees will eventually fail.  By observing tree structure, site conditions, work history, signs of decay, etc. we may glean some insight as to how likely failure will occur in a given time period.  Let's use the following example as a case study for likelihood of tree failure.

The specimen is a mature willow oak with a 30%-40% lean towards the North East.  Prevailing winds usually blow in from the South West.  The site is several yards from a creek that is known to flood, and the area received several inches of rain over the past few weeks.  Primary power lines are close to the tree. Utility pruning has been performed on the subject for decades, leaving an uneven crown with weight distributed on the leaning portion of the stem.

Upon closer examination Inonotus dryadeus conks are present on the tension side of the lean on the root flare.  Inonotus causes a white rot in the lower stem and structural roots of trees, and is common on willow oaks in this geographic area.  Resistance drilling tells us that up to 50% of the root flare is compromised by some form of decay/damage.
 

Finally, a live structural root, also located on the tension side of the lean, is cracked all the way through.

The culmination of these defects resulted in whole tree failure with property damage (thankfully, no one was injured).  The tree failed in the direction of the lean.

Notice the extensive root decay.

Here we can see partial root place failure due to wet soils.

This tree is an almost text book example of a high risk of failure tree, with final results as such.  As defects compound so does likelihood of failure.  That being said, I have participated in workshops where the same high risk of failure tree has been used for years, and still stands to this day.  Assigning risk and predicting failure is one of the hardest things we do as arborists.  Documentation and communication is key.  

The Root Collar, Oh No

By now we all know trees in the landscape, big or small, should have an exposed root collar. The root collar is the area of the lower trunk that flares out at ground level.  It is the transition area between the stem and the structural root system of a tree.

Tree root collars have evolved over eons to be exposed to air.  Buried root collars are detrimental for several reasons.  Cell respiration is disrupted, adding just one more stress to the tree.  This area of the tree can be intolerant to prolonged soil moisture, which can decompose tree bark and give way to stem pathogens.  Finally, buried root collars can lead to and disguise stem girdling roots.

Stem girdling roots arise in a few ways. When root collars are buried the tree reacts as if part of the root system has been damaged, and the tree forms a secondary root system.  These secondary roots can grow parallel to the stem, and begin girdling.  The other danger in this scenario, the secondary root system may take over water and nutrient uptake for the tree while the primary/structural roots slowly rot away.  Thus, a tree that looks perfectly healthy is standing with little to no structural root system.

Another way girdling roots develop on our landscape trees is through container production.  Many of the trees we plant are started in pots. When trees are allowed to stay in these pots for too long roots interact with the sides and begin circling the container. In many cases this is allowed to happen through every change in pot size, creating an almost hopeless structural root system.

With all that said, here are some pictures of messed up root collars and girdling roots:

Girdling roots around the circumference of the lower stem.

Large impacted girdling root, notice the diameter of the root compared to the diameter of the stem.

Severed girdling root, notice the large amount of stem damage that has occured.

What would you do for Liberty?

In 2010 an unknown assailant attempted to cut down a young tulip poplar in Charlotte's Freedom Park.  The vandal made it half way through the trunk before giving up.  While I know how many arborists feel about tulip poplars, this one was different.  This tree was grown from the seed of Maryland's original Liberty Tree.  You can read more about that story here: http://thequeenscrown.org/locations/6/Freedom-Park-Tulip-Poplar .

The Liberty Tree Tulip Poplar in the Summer of 2012

In an attempt to save the tree, horticulture staff installed guys in the direction of the damage and fastened steele plates adjacent to the cut.  Tulip poplars are fast growing trees, especially when young, and the idea was by stabilizing the trunk the tree will form reaction wood and grow over the damage.

After 2 years, see the amount of growth already put on by the tree.

Many of the prejudices we have about tulip poplars come from working on forest grown trees that suddenly find themselves in the middle of a suburban development.  Open grown tulip poplars can develop massive trunks with good taper, and are usually not as tall because reduced competition for light.  We think of tulip poplars as poor compartmentalizers, but the speed at which decay moves is relative, and may take decades to effect a tree that is today young and vigorous.

What would you do?  Would you have just removed it and said 'oh well.'  I think the horticulture department did the right thing, and because of these efforts we'll have an interesting tree to enjoy for years to come.

I'm Stubbed.

I've seen a rash of poorly pruned trees lately, and I think the picture below enforces why we should prune trees at the branch collar.  See the lower part of the branch forming callus tissue. This area is the remaining natural branch collar.

The rest of the cut is well outside of the collar, forming a stub.  You see how the tree has been unable to form reaction growth around this area.  This now leaves an entrance for pathogens, and may cause harm to the tree.  It also doesn't look very good.

Sometimes it isn't easy to get that final cut right, but its well worth your time.  Happy pruning out there.

Native Ash Trees: Oh No

I was at the ANSI IPM summit this week, and had the privilege to hear several industry leaders talk about the state of IPM. Dr. Mike Raupp from the University of Maryland was one of the speakers.  Dr. Raupp informed us the US stands to lose over 8 billion ash trees to emerald ash borer.

While this is tragic unto itself, something I hadn't thought of before was the effect on other species of plants and animals that have a symbiotic relationship with ash trees in the wild.  Untold numbers of animals use ash trees as primary food sources and shelter. In a greater view there are untold more animals that rely on the 1st bunch for food, seed dispersal, germination, etc.

So, what to do for these poor unfortunate creatures?  The Manchurian ash (Fraxinus mandshurica) has a natural resistance to emerald ash borer, and is similar to our native ashes.  Would it be possible to begin replanting our imperiled ash forests with Manchurian ash? If it is, could we save numerous species of plants and animals from possible extinction, assuming this Asian ash species would be a suitable substitute for our native ash?  Or would this exotic ash fall victim to a native pest our endemic ash has long since built resistance to?

These are interesting questions, and play a role in the future of our landscapes, forestry, and conservation arboriculture.

Manchurian ash, could you tell the difference.

The Scourge of Imidicloprid

If you're like me, then while your wife is looking at power tools at Home Depot, Lowes, or wherever, you are looking at the active ingredients on pesticides in the garden aisle.  Which means you have probably noticed that many general purpose over the counter insecticides are now imidacloporid based.

As an industry, we have relied on imidacloprid, Merit in its most popular form, for more than a decade.  Applied properly it is a great product.  It is in the neonicotinoid family of chemicals, and its mode of action is kind of neat.  The chemical interferes with an insects nervous system which results in death. Imidacloprid can be applied as a foliar spray, soil application, or directly injected into the trunk.  It is nontoxic to mammals, has a long residual, and can be quite effective.

However there are some things we need to consider when using this pesticide.  Studies have shown that with repeated use the molecule can make its way into the flowers of plants.  For trees and shrubs that are not wind pollinated this exposes pollinators to the product, and may lead to civilian casualties in the war against plant pests.

The other issue is pest resistance to imidacloprid.  In some areas imidacloprid has been so heavily used that it is no longer effective against targeted pests.  With imidaclolprid now being readily available to the public at large, and continued reliance on the chemical in many professional PHC programs, we may only assume that this pest tolerance will grow.

There are few 'silver bullets' in pest management.  Product/chemical diversity is an important part of an IPM program.  Imidacloprid may still be part of your chemical arsenal  but pest monitoring and investigating different products for use on target pests should be on the forefront.

The molecule