A Day With Dr. Alex Shigo

 

Baldcypress (Taxodium distichum) trees are one of the trees recommended by Dr. Alex Shigo to be planted in city conditions.  The Baldcypress tree in this picture is on the Campus Drive side of St. Mary's Residence Hall on the University of Maryland campus.



Recently, while rummaging through some old notebooks filled with plant information, I found some notes that I made from a conference or symposium given on June 5, 1994 by Dr. Alex Shigo.  Dr. Shigo has been dubbed by some people as the 'Father of Modern Arboriculture.'  Many foresters and horticulturists just need to hear the name 'Shigo' and immediately know who that you are talking about.  At the time I made these notes, I was living in Lincoln, NE and working as a landscape designer for Campbell's Nurseries.

Growing up in Kansas, a plains state where the vast open prairie was once king, trees were a rare and treasured commodity to me.  I loved looking through books such as The Audubon Society Field Guide to North American Trees.  The seductive glossy color pictures showed exotic leaf shapes that I had never seen before and bright fall leaf colors that were very alluring. 

Trees are big, up in your face type of plants that demand to be noticed.  They are much easier to pick out as individuals from a greater distance than most other kinds of plants.  Sometimes, trees within a species can appear to be be different from one another due to various environmental conditions or trauma that they have encountered over the years.  Prairie grasses with their fine bladed, herbaceous leaves are much harder to distinguish as individuals than trees with their their large woody trunks; however, in vast numbers in a tightly spaced community, grasses can work together with forbs, an unfettered view of the sky and the sometimes sparse accents of shrubs and trees to create quite dramatic landscapes.  Because trees can be distinguished as individuals and are usually long lived, it is easier to have an emotional attachment to them than other kinds of plant.  Great grandmother's treasured fern leaf peony that has been lovingly handed down through the generations might be an exception.

When I saw the information the Dr. Alex Shigo would be speaking at the spectacular and recently constructed Lied Lodge & Conference Center, part of the Arbor Day Farm in nearby Nebraska City, NE, I decided that this was an opportunity that I did not want to miss out on.  I was not disappointed.

Dr. Shigo's opening statement was 'Training without education is subjugation.'  As soon as I heard that statement, I knew that we were going to be in for an intense day of training by someone that was very passionate.  While today I do not remember what Dr. Shigo looked like, there were some concepts and information that Dr. Shigo introduced that day that made a big impression on me and have stuck with me and been a part of my thinking on trees ever since.  While many years have passed since that day, the information that he presented is still accurate and unfortunately, still unknown to many that it would be helpful to.

One of the first points that Dr. Shigo made that was that you cannot expect instant results with correct tree pruning methods.  It takes 5-6 years before that you or your neighbors will notice a difference in the way that the trees are pruned.

Below are some scattered notes on concepts and examples that Dr. Shigo gave that caught my attention:

• 'In Denmark, trees are root pruned 4-5 times before leaving the nursery'.  He was a big believer of root pruning in nurseries.  Shigo insisted that you need to make clean cuts when root pruning.  Most American nurseries do not root prune that often to my knowledge.
• 'Well paid people are people paid for making decisions.  We are paid for making correct decisions'  I think this statement was related to if you (an arborist or tree care professional) just do what a customer asks without alerting the customer to the fact that what they are asking you to do is not a good tree management practice, you will not be able to ask a decent price for your services, given the probable bad end results.
• Do not mix trees that like dry conditions in the same planting with trees that like wet conditions.  The different water requirements will kill one group of trees when you have an automatic irrigation system that does not allow for this differences in water requirements.
• 'Trees should be planted in clusters rather than singulary'.
• When transplanting, 'the smaller the tree, the better for long term survival.'  Recently, the wife of a former college roommate that now lives near Emporia, KS asked me on Facebook what kind of trees she should consider planting that she would likely have good results with as she had very poor results with some maple trees that she had previously planted.  When I suggested that she plant an acorn from some oak trees native to the area where that she lived, I think she was quite shocked and thought that I was joking as a reply quickly came back 'PLANT AN ACORN???  Seriously, ....'   
• Absorption of many nutrients by a tree's roots happens during the winter.  Mycorrhizae that surround tree roots can help keep the soil from being frozen in that immediate area.  Mycorrhizae can also help aid in the absorption of nutrients by a tree's roots, much better than a a tree's roots can on their own without the help of mycorrhizae.  The pH can vary by up to 2 points from the soil to within mycorrhizae.  This can be very helpful to uptake of nutrients as the availability of nutrients in the soil is pH dependent.  Snow and leaf litter can also aid in keeping the soil from being frozen in winter, allowing the absorption of nutrients in winter.
• Composted mulch (ground leaves and twigs) is a good product to use to encourage the growth of mycorrhizae.  Mycorrhizae do not grow well in compacted soils.  Shigo felt that a thin application of composted mulch was better than a thick one and that it would be better to mulch two to three times per year.  He mentioned that Disney World mulches 3 times per year.  This concept may be a hard sell to people on a tight budget as weeds will likely come up in a thin mulch and additional money will have to be spent on weed removal and the reapplication of mulch.  Application of fresh wood chips brings with it the possibility of undesirable pathogens that may harm a tree.
• 'Healthy mycorrhizae on a tree keep pathogens away that can cause problems.'
• 'Mycorrhizae live at least a year while root hairs come and go quickly.  Root hairs live only a couple weeks.'
• 'Do not stake trees or they will become weak.' 
• 'Oak roots can be like carrots, bigger than the above ground parts.  Pull up a 1/2" caliper maple and then challenge an unsuspecting friend to pull up a 1/2" caliper oak.'
• 'Temperature really affects photosynthesis.  Photosynthesis stops when temperatures reach over 100 degrees Fahrenheit.  Photosynthesis moves into the interior of trees on hot days.  You need leaves on the inside of a tree because of this.  Do not clean the leaves out of the center of a tree!'
• 'Tree wounds spread less if that they occur in spring.  They spread more severely in the fall.'
• 'Do not drain slime flux by drilling and inserting tubes as the holes open up new sites for disease spread.'
• 'Cut close to the tree collar, whether it is close to or far out from the trunk.  Flush cuts create internal cracks.'





Blue lines show where that the last saw cut should be made just outside of a branch collar on a Crapemyrtle tree in order to remove the branch.







The saw cut made to remove this branch on a Goldenraintree (Koelreuteria paniculata) appears to have been a flush cut.  Notice the decay inside of the wound and how little callus tissue has formed around the outside of the wound.  Also, there is no bulge away from the tree trunk.  The cut appears to have been made inside of the branch collar rather than outside of it.







A dead branch was allowed to remain on this Sawtooth Oak (Quercus acutissima) a number of years before being removed.  The edge of the callus tissue that is closest to the trunk is where that the cut should have been made at the time that the branch first died to remove it.  The wound would have healed much faster.  If no branch collar is visible which happens on some trees, the angle shown in this photo is generally a good angle to cut to remove a branch.






Excellent removal cut on a Goldenraintree (Koelreuteria paniculata) that was made just outside of the branch collar.  If you cannot detect a branch collar, this is generally a good angle and distance away from the trunk to cut.









A good removal cut was made on this Crabapple (Malus sp.) tree.  The callus roll that forms the doughnut shaped ring around the wound appears to be very healthy and healing relatively quickly.






This photo shows a branch collar on a Sugar Maple (Acer Saccharum) that has formed at a quite unusual angle.  The blue lines show where that the recommended last cut be made in order to remove the branch.  These blue lines are just outside of the branch collar. 

 



Completely healed wound on a Crabapple (Malus sp.) tree.



• 'Trees need a continuing supply of energy.  Do not cut roots and the top both at the same time.  Your are reducing the energy, either stored energy or future energy to be captured by the sun.  Don't worry about trying to balance top and roots by pruning.'  Independent research by prof. Carl Whitcomb of Oklahoma State University backs this up. 
• Do not prune the top of a tree when planting, come back a year later and prune the top then if needed.
• 'Everytime that a sprout comes up, you have adversely affected the energy of the tree.'  My comment is that the more branches you remove from a tree, the more likely you are to see adventitious sprouts form.  That is not a good thing!
• 'Crabapples send up sprouts when planted too deeply.'
• 'Enthusiasm is infectious.  Show customers how excited you are to be on their property helping them out.'
• 'Indeterminate type trees that are fertilized late will continue to grow and not have the chance to form up energy carbohydrates that will allow the apical bud to have enough energy to emerge the following spring.'  This will cause the tips of twigs to die back.
• 'First buds of planetrees do not have enough energy to withstand anthracnose, while the secondary buds have more energy in the and are more resistant to anthracnose.'





Anthracnose on Sycamore or American Planetree (Platanus occidentalis).


• Trees with thin bark such as birch, beech and planetrees can have photosynthesis occurring in the cortex of the tree.  This means that in these kind of trees, photosynthesis can occur in the twigs, branches and trunks of young trees.  These kind of trees can conduct photosynthesis on rare warm days in the winter.  Do not wrap the trunks of these trees as you block the sun and interfere with the process of photosynthesis.
• Some young trees with living cells in the center of the tree such as planetrees for example can live five to six years after being girdled.  Most temperate zone trees do not have this capability.
• 'Over pruning of trees is done to let customers know that the arborist was there.'
• 'As trees get older, 90% of the pruning should come from dead wood.
• 'Planetree and Catalpa are good species for the practice of pollarding.'  I wonder if Catalpa bignonioides 'Aurea' would make a good specimen or feature plant in the right location when pollarded.  Pollarding would certainly allow it to grow in a much smaller area.
• On the west coast of the USA, many people take out too much wood on trees past maturity which often yields the unwanted result of Armillaria root rot.
• 'Trees that do well in cities also tolerate wet soils.  Baldcypress make good city trees.'
• 'You have one year after planting a tree too deep to pull the soil off of the top.'  
• 'Burlap left in planting holes can last 20 years and will restrict root growth.'  I have personally seen untreated burlap last as least 5 years in planting holes and certainly agree with Dr. Shigo that as much of it as you can remove should be removed before filling in the planting hole. 
• After removing the burlap on a tree root ball, cut off the bruised and torn roots cleanly.

This landscape installation crew is removing the burlap and manila cords or rope after that the tree has been set in the hole and stabilized.  Removing the burlap from trees when planting was one of Dr. Shigo's recommendations.



The landscape installation crew is back filling the hole after removal of the burlap that covered the root ball of the tree.



• Do not apply nitrogen to a newly planted tree.  Sucking insects come when too much of the energy reserves intended for defense are used up in growth.
• Plant on a mound if you have a tight clay soil with poor drainage that does not support the growth of trees. 
• 'Improper grafting causes sun cracks on most fruit trees, not winter cold.'
• It is best not to use tree wrap on trees.
• 'Resistance to decay comes from within the plant which is why wound dressing does not work.'
• Floods kill mycorrhizae which in turn leads to the death of obligatory trees (trees that rely totally on mycorrhizae).  Those trees that do not require mycorrhizae can probably survive a flood.
• Roto-tilling under the canopy of a tree is the worst thing that you can do to a tree.  Piling soil around a tree is the next worst thing that you can do.  These two comments by Shigo pretty much eliminate the possibility of being able to successfully grow most annual flowers underneath of the canopy of trees if you want to continue to have healthy trees.
• Roto-tilling will open up many jagged wounds that will attract disease organisms.

The above was just a small fraction of the information that Dr. Shigo presented that day.  He presented detailed support of his concepts, which for the most part I left out of my above notes.  If any of the above information interests you, I would highly recommend that you visit his official website for more detailed information.

Dr. Shigo was a very generous man as he issued an open invitation to all attendees that day to visit him in his laboratory in New Hampshire.  Dr. Shigo died on October 6, 2006.  His passing was a huge loss to the forestry and horticulture communities.  Fortunately, Dr. Shigo was someone willing to pass his information on to others and record it for future generations!