What could it be? I hope it doesn't suck....

Take a look at the picture of the Nelly Stevens holly below.  You'll notice the top of the tree is in decline.  What could it be?  Root rot? Nutrient deficiency? Perhaps straps where left around the stem and are now girdling the tree...

Now let's take a closer look...

Upon closer inspection we see the top die back is being caused by coalescing sap sucker wounds.  The yellow belly sap sucker drills holes in over 1000 species of trees.  The purpose of this behavior is to feed on the high sugar content tree sap, and any insects that may get caught in it. Sap suckers form two kinds of holes.  The first is a round hole that extends far into the tree and is not enlarged.  These are the holes that are commonly associated with species like sugar maple.  The second is a square hole that is shallow, but which needs to be be constantly maintained for sap flow.  It's this square hole that I've seen kill whole branches of trees over the years, most notably holly species. 

There aren't any good ways to prevent sap suckers from enjoying your trees.  Repellent sprays on the market seem to not be effective.  For high value trees I've seen burlap being wrapped around trunks during times of sap sucker activity.  This provided some modicum of protection, but can be unsightly and labor intensive.  In the interest of political correctness, I'll refrain from any BB-gun jokes.

It starts at Day 1

When we take a tree from its native environment and plop it in the middle of the landscape, we're taking on a lot of responsibility.  The seemingly simple step of planting a tree can be the most important moment for the plant over the course of its life.

In the picture below are two oaks planted at the same time and at the same size.  The tree in the left of the picture was planted with the root collar exposed and at the proper grade.  The tree to the right was planted with root collar well below grade.  Several years down the line the correctly planted tree is far out performing the improperly planted tree.

The precedent for how these trees will function in the landscape was set on the day they were planted.   Proper planting, soil moisture, soil texture, etc. all play a part in how our trees will survive. Attention to detail is important to the long-term success of any introduced tree in our landscapes.

Zombie Tree

One theme I can't emphasis enough is that trees don't want to die.  Over millions of years, these large woody plants have found ways to overcome all kinds of ordeals.  We often try to predict tree failure and mortality by quantifying visible and perceived damage.  If said damage exceeds some measurable threshold, then that tree is often slated for removal.  But trees don't always fall in line with what we think is so certain.  Take for instance the tree pictured below.

At some point in time this tree met with some accident.  Significant area of trunk circumference was damaged.  Upon initial inspection, most of us would probably not give this tree much chance of survival.  Now there is no telling how long ago the damage occurred, but if you look closely you'll see the extensive amount of wound wood growing over the damaged area.  Some may say this is unprecedented, but I say it's a tree showing us that there are exceptions to every rule, and those exceptions seem to be exceptionally common in arboriculture.

The arrows highlight areas of the tree where wound wood is forming around extensive trunk damage exceeding 30%  of trunk circumference.

Tippy trees.

Some trees lean.  Leaning trees are a natural phenomenon in nature.  While there are many reasons why trees lean, most of the time the reason involves the search for light.  This is called a phototropic growth response.  Trees growing in this manor put on adaptive growth and reaction wood to maintain stability.

Once a tree has grown to a point where there is a clear view of the sky the lean will 'self correct,' and new growth will begin to grow with a more vertical orientation.  At this stage the stem lean should be at its maximum, and if the tree remains structurally sound the angle of the lean should remain constant.

Look carefully at the pictures below.  The picture on the left is a screen shot from Google Street View of a post oak taken in 2011.  The 2nd picture is of the same tree taken in December of 2013.

2011                                                                                       December 2013

Notice the difference in orientation of the lean.  The root collar of this tree is not well exposed.  The homeowner indicated she noticed a change in the lean of the tree in July of 2013, and was aware of at least one 3- to 4-inch diameter root that was severed to install the brick walkway earlier that same year.  After some peripheral probing with a soil knife to about 6-inches deep, no structural roots were detected on the tension side of the lean. 

Could this tree be actively failing, albeit slowly?

Back in the day.

I just started getting into the book 'Tree Disease Concepts' by Paul D. Manion.  The book has been out of print for some time, but Dr. Glen Stanosz mentioned it as a good resource at his talk during the recent TCI Expo here in Charlotte, NC.  By some serendipitous alignment of the stars, a retiring arborist friend of mine had given me the book just weeks beforehand.

The book begins with a historical perspective of plant diseases.  Around 300 B.C.E. the philosopher Theophrastus, known to many as the father of botany, 'recognized that wild trees were not liable to the ravages of disease, whereas cultivated plants were subject to an array of devastating diseases.'  This seems very interesting to me.  Since ancient times humans have, with the best intentions, been trying to grow plants, but missing the big picture when caring for them in the landscape.  The battles of poor cultural management we arborists fight on a daily basis, have probably been taking place for eons!  Imagine mulch volcanoes on olive trees planted around the Acropolis.

Another thought; we are members of a global economy.  Because of shipping and imports, numerous tree diseases and pests have been introduced to the US.  Around the time of Theophrastus Greece was the center of a global economy.  One may wonder how many of the diseases ravaging the urban trees of Ancient Greece were introduced from afar.

Theophrastus, the father of botany.
Pic borrowed from Wikipedia (you should donate to Wikipedia)

Where they headin'?

Recently, a study by US Forest Service Researcher Christopher W. Woodall reported that 70% of 'northern' tree species are regenerating significantly further north and/or at higher elevations than their mean biomasses (where most of the mature trees of that species historically grow).  If the current trend stands, many northern tree species' biomass may migrate up to 62-miles (100-kilometers) over the next century.  Other species' range appear to be decreasing all together, though they may be thriving in Canada since this study only sampled trees in the United States.  While northern tree species are retreating northward, southern species are having greater seedling success at higher latitudes, and some signs show that some southern species may begin invading even more southern latitudes.

Bob Dylan said 'the times they are a-changin,' and many researchers would agree.  Now we can debate whether climate change is real, and whether its causes are natural or man made, but for the sake of argument let's agree something is happening with our climate.  Our question is 'what about our urban and landscape trees?'  The affects of climate change on tree species may be somewhat predictable.  Decline diseases on sensitive tree species may become more pronounced, thus shrinking the area suitable for them to grow.  While other, more adaptable, species may thrive in greater ranges.

We can look at this as both a challenge and an opportunity.  The challenge will come from trying to preserve some well-loved and traditionally planted landscape species.  Pest and disease ranges will likely change as well, and so our management strategies will need to adapt.  But in some instances, there will be opportunities to introduce and diversify our landscapes with new plant species/varieties.  I know I wouldn't mind having some nice flowering oleander (Nerium oleander) in my, for now, zone 7 garden.

Check out your hardiness zone.

Remember to sweat the small stuff.

Every time we apply a product to solve a plant 'problem' we are changing the environment in some way.  The collateral damage caused by our plant heath care actions can range from minor to catastrophic; for example, the large bee kill in Oregon this past year.  Even soil-applied fertilizers will affect soil chemistry in unintended ways.  High concentrations of some plant essential elements can be antagonistic to other plant essential elements, making them unavailable for uptake.

We have a responsibility to take proper precautions, make accurate diagnoses, and know what and how things we are doing will affect the world around us.  Our management goals should be based around having as little impact as possible, and in the end, introducing as little outside product as possible in to the environment. As arborists we are expected to be stewards of the environment, and this is something we shouldn't take lightly.

Something that seems as unintrusive as applying an adhesive band to the tree can capture a range of off-target insects, reptiles, and mammals.