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.

The construction conundrum.

This week we have a guest writer featured on the Wandering Arborist. Brandon Hogan is an ISA Certified Arborist & Municipal Specialist, and is ISA Tree Risk Assessment Qualified. Currently he is a sales consultant at Heartwood Tree Service in Charlotte, NC, but has also had an opportunity to travel throughout most of North America creating tree inventory and management plans. Enjoy.
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There are two major concerns when trying to preserve tree(s) within construction sites.  The first is preventing physical injury to the tree in the form of damage to branches, trunk or roots.  The second is soil disturbance in the form of compaction and changes to the grade or elevation of the soil.  Preventing physical injury to trees during construction can best be accomplished through installation of a physical barrier between the worksite and the tree.  This area is designated as the Tree Protection Zone and serves not only to protect the tree from physical injury, but also minimize the disturbance to the surrounding soil.  

Physical injury to a tree can lead to a wide variety of issues depending on the location and extent of damage.  Wounds created through improper pruning, careless equipment use or root severance can open the door to pest, disease, or decay issues in many trees.  Soils are where trees, live so protecting them is vital for any tree.  Soils can be easily damaged through compaction created by mechanical equipment or the storage of heavy materials (bricks, stone, etc.).  Compaction creates an environment below ground that will be less conducive to root growth and health.  The addition or removal of soil near a tree can also have a negative effect on its health.  Removing soil can damage roots and adding soil can suffocate them.  In addition, even grade changes a good distance away from the tree can change how water flows through a site and how much will be available to the tree in the future.  

Tree where absolutely no thought is given to preservation.

Ideally the Tree Protection Zone would extend outward from the trunk of the tree in a circle to the outer limits of its canopy (drip zone).  Usually coordining off this large of an area within a construction site isn't feasible.   In this case, protecting as large an area as possible within the tree’s drip zone is recommended.  Generally, the minimum acceptable distance for the Tree Protection Zone from the the tree would be a circle extending out from the trunk a distance of 3Xs the diameter of the tree, measured at 4.5 feet above ground.  Excavations leading to root severance within this zone can create structural issues that may warrant the removal of the tree.  By severing large roots very close to the trunk, not only is the tree’s ability to extract water, nutrients, etc. from the soil compromised, but also its ability to anchor itself to the ground.  

Here an effort is made in erecting tree protection.  While the trunk seems well protected, little thought is given to protect valuable soil.  Care should be taken to preserve as much undisturbed soil as possible. (PA)

Not every tree is a good candidate to try and preserve through a construction project.  There are several other steps that would need to be taken both before, during and after the construction project to ensure the tree remains healthy and stable.  The steps will vary with each tree and site.  Protecting the soil and tree itself during the construction is a practice that will apply to any site.  The larger an area that can be protected around the tree the better chance that tree will have of remaining for many years after construction is completed.  

What big thorns you have.

Have you ever noticed the thorns on a honey locust and thought to yourself 'what's goin' on with those big daggum thorns?'  Honey locust evolved along side the Pleistocene megafauna.  Extinct animals such as woolly mammoths, mastodons, and giant sloths used to roam North America, and likely fed on the seeds of honey locusts and water locusts.  

These trees depend upon large mammals eating their seeds and passing them through their gastrointestinal tract out as a way of dispersal.  But inviting a 5-ton animal to dinner can be dangerous, thus the reason for thorns that can be 8-inches long.  The prehistoric mammal gets a meal, the tree's seeds are spread, and the thorns keep the dinner guest far enough away from the tree so it can survive to make another crop of seeds next season.

Next time you see a honey locust just imagine, one of it's ancestors probably grew because a woolly mammoth pooped it out somewhere.

Honey locust thorns, they'll take your eye out.

The Band, a spray alternative.

When controlling pests on trees and shrubs we often think of spraying some kind of chemical product, and while this is often our only course of action, for some pests there are alternatives.  Many pests can be physically removed.  Webworms and tent caterpillar nests can be pruned out or destroyed.  White peach/prunicolia scale can be scrubbed off the stems of small cherry laurels and lilacs.

Another non-chemical method for preventing pest injury to trees is creating a physical barrier.  This is most effective against certain species of lepidoptera that climb from the ground in to the canopies of trees to feed or lay eggs.  In the Charlotte, NC metro area there's an unprecedentedly large population of fall cankerworms (Alsophila pometaria).  There are many theories as to why cankerworm numbers are so large, but no doubt part of the problem lies within the overwhelming number of mature willow oaks (Quecus phellos) lining streets and gracing private yards.  

Cankerworm adults emerge from the ground after the 1st series of cold nights (at or below freezing) in the late fall/early winter.  The adult female cankerworm doesn't have wings, and is forced to climb up the trunk into the canopy of a tree to mate and lay eggs.  Each female can lay  between 100-200 eggs.  In spring, just as leaves are approaching full expansion, the little inching cankerworms emerge from their eggs and feed on the tender young foliage.

These cankerworms are present in such damaging numbers that the city of Charlotte, and most of her residents, habitually affix bands covered or lined with sticky stuff to trees throughout the fall.  This way cankerworms are controlled safely and economically.

Heartwood Tree Service Arborist affixing 'Bug Barrier' to the trunk of a willow oak.

Is it over reacting?

Trees respond to damage or decay by forming reaction wood.  The placement and extent of reaction wood can be telling of where and how long the tree has been affected by decay.  When we think about a tree responding to decay organisms,  most often our first thought is the compartmentalization of decay in trees (CODIT) model.  However, the CODIT model is based upon a tree's reaction to damage to the bark and cambium.  When decay enters from the tree's structural root system, or perhaps an old tap root that has died off, trees react a little differently since the decay organism is growing in duramen (heartwood) tissue, which is effectively dead structural tissue.

The root flare of the willow oak pictured below has been quite disfigured by years of attempting to out grow Inonotus dryadeus and Ganoderma lucidum.  When sampled with an IML-Resistograph, what appears to be a substantial amount of wood reveals areas and pockets of substantial decay.