Sunday, October 28, 2012

I Like Red Maples

Really I do, and at this time of year as their leaves are turning different shades of red, I can't help but think they are not as bad as many arborists make them out to be. Sure I've been known to role my eyes at thought of planting another 'October Glory,' but in October I wish I had one in my yard.

Red maples in the landscape get a bad wrap. They are produced in the millions by growers, and by the time they make it to retail there are layers of pot bound induced girdling roots, and the root flare is almost hopelessly buried. Lack of young tree pruning and disregard for proper crown structure leave them prone to co-dominate stems, included bark, and branch breakage. But aren't these true of many species by the time they make it in the landscape, and maybe we just notice it more on red maples because there is just that many more of them?

Red maples as a species are incredibly versatile. Native red maples grow through out the Eastern U.S. from low land swamps to rocky hillsides.  They are like a native super tree.  This species is planted in the landscape from Florida to British Columbia. Except for gloomy scale in the South East there are no more pest problems with red maple then with any other landscape tree. And even in the South it isn't uncommon to see a red maple planted to deep in a parking lot, with girdling roots, and covered in gloomy scale, and though not looking good, still surviving.  So take a break from hating on red maples and enjoy some fall color.

Friday, October 19, 2012

Trees Don't want to Die: A Musing

Trees have been around for millions of years, and they have found ways to survive outside in all kinds of conditions. We as humans try to understand why trees die and fail, and how to predict these events. Along the way our industry has come up with 'rules of thumb' to help us predict this. We hear arborists reference numbers like 30%, 33%, or 70% to quantify chances of tree failure or death, but trees break these rules on a daily basis.

There are 'high risk of failure' trees, condemned years ago, still standing today.  These trees have stood through wind and storms which have toppled other trees.  I've seen mature oaks with more than 50% of their trunk circumference damaged from the ground to 20-ft up the stem that are green and vigorous, and which have had enough energy to form callus tissue around the damage.

My view is becoming not, 'we have this much strength loss,' but instead 'we have this much strength left.'  And the same when it comes to the vascular tissue.  We must realize, of course, that some of this will be species, condition, and site dependent.  But, if a tree has 32% of it's root-flare compromised by decay is it a moderate risk of failure, while at 33% it is a high risk of failure?  Or, is what matters the 2 or 3 root flares not damaged are strong enough to support the weight of the tree even if even if all the other flares were compromised? How long will a tree with 50% of the stem girdled maintain a health canopy? 1yr, 5yrs, or 10yrs?  These are the questions I ask myself, because I don't want to remove a tree until it is necessary  and most of my clients feel the same way.

Notice how this tree has fallen completely over, and yet it continues to put out growth maintained by just a small portion of vascular tissue.

Sunday, October 7, 2012

Tree Root Failure: A Discussion

Earlier this week an arborist friend and I were discussing root failure.  The discussion revolved around, if roots were severed, which direction would the tree fall.  His argument was the tree would fall towards the severed roots, while my argument was the tree would most likely fall away from the severed roots.  I believe my argument, the tree would most likely fall away from the severed roots is supported by a publication from the University of Georgia Root Strength  & Tree  Anchorage.

Root failure occurs in association with wind load and gravity.  'Beyond the root plate area, root tensile strength becomes more critical to anchorage.'  That is, as the wind blows roots on the wind ward side of the tree, the tension roots, are doing the most work.  Relatively speaking of course.  If these roots should be severed or damaged the tree would fail in on the opposite side of the force, or away from the root damage. Mattheck describes the roots on the tension side of the tree as forming holding knots in the soil.  Again, considering damage to the tension side of the tree will give a hint to where the tree may fall.

In addition to these references, I have also seen trees that are root decayed fall opposite the decay.  Now I could be wrong in my conclusion, but I think I make a pretty good case.  Some other interesting information from the UGA publication:

-'To summarize, a few large diameter and long roots can not provide effective resistance to failure.  It is in the proliferation of smaller roots in consolidation of the root plate which provides anchorage success.  (Stufka & Kodrik 2008)'

- 'Compression strength increases for a short distance from the stem base before declining with length.  Root compressive strength was found to be roughly the same for angiosperms and gymnosperms, but bending strength was found to be much greater in angiosperms. (Stokes & Mattheck 1996)'

-'Anchorage is concentrated in two general locations around a tree base: 1)  close to the stem base on the
leeward side and focused on several large diameter roots; and,  2) farther away from the stem base on the windward side in many, smaller, large surface area, near-surface roots.  (Danjon 2005)'

-'Windward roots have forces applied which are concentrated approximately 1.5X (one and one-half times) farther away from the stem base than leeward roots.  (Stokes 1999)'