Tree Risk - notes

 Notes from Tree Risk Assessment Qualification (TRAQ) class taught by Kevin Eckert for the Arizona Community Tree Council.  October 2022 

About 25 people are killed each year by falling trees in U.S.

Removal should only be an option when mitigations are not sustainable.  We have an ethical obligation to do no harm.  The benefits of trees are important.  

A risk is meaningless without a time frame.

Imminent - if a tear in the tree is weathered, the failure is not Imminent

Probable - failure would likely occur during normal (expected/seasonal) extreme weather.

Possible - failure would likely occur during abnormal (hurricane, tornado, derecho, etc) extreme weather.

Wounds

Thicker sap trees tend to compartmentalize better

If sap is oozing, touch and smell it:

Sticky = ok, its sap

Sour = bacteria

Slimy or foamy = fungus

Wet = just water

Drought

Tree dying from bottom up is over-irrigation

Tree dying from top down is drought (under-irrigation)

Failure

Soil failure vs root failure:  roots in air or roots break and stay in ground

Codominant is not a fault.  

Included bark is a fault because weak area doesn't hold stems.  

Aspect ratio near 1:1 for codom stems is a fault because don't have enough wood to wrap around union.  This is common cause of failure in pines, especially CA fire investigations.

Decay

Worse on compression side and at the base.  Hollow poles are strong. Most stress in tree is around the shell, so sapwood carries most weight, not heartwood (which is more brittle).

Heartwood - least concern

Sapwood - will start seeing tip dieback. 2nd worst.

Root - will also see tip dieback.  Not too bad if not structural; crown dieback will balance root dieback.

Basal - worst.  

Types of Response growth:

Reaction wood from tension/compression

Flexure wood from movement

Wound wood - e.g. lip around wound. More growth shows more stress

Likelihood of failure increases/decreases based on load (e.g. wind exposure) / response growth

Stress

Reproduction is sign of stress in trees (plants):  orchard trees cut to fruit more, but decreases lifespan.

Vigor/health does not always reduce tree failure risk

Adding N can increase leaf area and stem elongation, but that can increase load on stem and if stem doesn't thicken then can increase tree failure risk, even while increasing tree "vigor".  Sometimes reducing growth (ie use growth regulator) can improve mitigations.

Sheer plane: where tension and compression meet

Cracks: transverse (fiber failure) or longitudinal (with the grain)

Age

Old trees: retrenchment = natural process of aging, shortening and widening = more stable

Trees naturally move with wind.  Mass damping shows importance of inner branches and leaves.  Helps tree stems "undulate like snake in the wind".  Sharp bends or lack of inner leaf area can inhibit natural movement.

Construction

New concrete can leach lime/calcium oxate which raises soil pH and can harm some plants if too much

Adventitious branches = "water sprouts" (from topping = non ANSI cuts) = epicormic.  Poor attachments can rip out.

Shigo said:  "don't err on the side of safety….just do it right!"  :: Do the best you can based on your education, training, and experience.  

What Causes Colon Cancer? More importantly, what prevents it?

Colon cancer incidence --like that of many cancers-- varies several-fold between different countries, indicating that perhaps there are environmental or lifestyle factors that cause or prevent it. Much of this post is based on this excellent review article

Known Influences of Colon Cancer Risk (ranked from most important to most equivocal)

Aspirin: The Women's Health Study of 34,000 women 45 years and older found a 42% reduction in colonrectal cancer in the group that was taking aspirin.

Selenium: Populations with adequate selenium intake (most of the U.S. is OK, but European soils are selenium-depleted so their foods are lower) have lower colorectal cancer.

CLA, or conjugated linoleic acid is protective against cancer and found in grass-fed beef and dairy products, possibly explaining a lower incidence of colorectal cancer among people who eat dairy.

Dietary fat: results are conflicting. While a study based on a large, hospital-based sample of cases and controls, provided no evidence that dietary fat was associated with increased risk15, an equally large and well executed case-control analysis revealed a strong association of dietary fat with colon cancer risk 16.

Fiber: results are conflicting. One of the best studies of diet and colon cancer, the prospective Nurses Health Study, indicated that dietary fiber does not affect the risk of subsequent colon cancer 17. Although some fruits and vegetables, which contribute fiber to the diet, may be protective, dietary fiber alone appears to have no impact on colon cancer risk17.

Vegetarian Diet: while eating a vegetarian diet slightly lowers the risk of all cancers, it has also been found to increase the risk of colon cancer, according to the European Prospective Investigation into Cancer and Nutrition (EPIC) study.

Meat: results are conflicting, and different for different types of meat.  “The available epidemiologic data are not sufficient to support an independent and unequivocal positive association between red meat intake and CRC [colorectal cancer].” - from a review of the evidence regarding red meat consumption and colon cancer in the European Journal of Cancer Prevention [1]. Cited by Dr. Briffa.

However, a number of compounds in meat are known to be harmful.  For example, heterocyclic amines, a known cancer-promoting substance, are produced when meat is grilled or fried at high temperature.  High iron levels may induce oxidative stress and can be harmful.  Meat increases IGF-1, which promotes growth of all cells, esp. cancer. Recently, a sugar in red meat called Neu5Gc has been linked to inflammatory effects.  And even Carnitine, a heart-healthy compound found in red meat, has been found to stimulate bacteria to produce TMAO, a known cancer-causing substance.  However, whether all of these individual compounds, when consumed as part of a healthy diet, cause cancer, has yet to be determined.   Chris Kresser has comprehensive review article that addresses these complexities in greater detail.  

[1] Alexander DD, et al. Meta-analysis of prospective studies of red meat consumption and colorectal cancer. Eur J Cancer Prev. 2011 May 2

Risk Assessment

Nuclear and chemical technologies (except for medicines) have been stigmatized by being perceived as entailing unnaturally great risks.

R. Gregory, J. Flynn, and P. Slovic, ‘‘Technological Stigma,’’ American Scientist 83, 220–223 (1995).

The social problem is compounded by the fact that we tend to manage our risks within an adversarial legal system that pits expert against expert, contradicting each other’s risk assessments and further destroying the public trust. The young science of risk assessment is too fragile, too indirect, to prevail in such a hostile atmosphere. Scientic analysis of risks cannot allay
our fears of low-probability catastrophes or delayed cancers unless we trust the system. In the absence of trust, science (and risk assessment) can only feed public concerns, by uncovering more bad news. A single study demonstrating an association between exposure to chemicals or radiation and some adverse health effect cannot easily be offset by numerous studies failing to and such an association.

Psychometric Factor Analysis of Risk Perception: Dread Risk and Unknown Risk

Risks are perceived based on their qualities.

Micromorts can be used as an "objective" statistical approximation of risk.

"Substance X causes cancer in animals...."

Consider two statements, S1 and S2: S1: ‘‘Would you agree or disagree that the way an animal reacts to a chemical is a reliable predictor of how a human would react to it?’’

The second statement, S2, is a little more specific: ‘‘If a scientific study produces evidence that a chemical causes cancer in animals, then we can be reasonably sure that the chemical will cause cancer in humans.’’

How did you respond? How would a scientist respond?

from P. Slovic, ‘‘Trust, Emotion, Sex, Politics, and Science: Surveying the Risk-Assessment Battlefield,’’ in Environment, Ethics, and Behavior, M. H. Bazerman, D. M. Messick, A. E. Tenbrunsel, and K. A. Wade-Benzoni (eds.) (San Francisco, New Lexington, 1997), pp. 277–313.

How much is a human life worth?

From a 2008 article in the Washington Post: Several federal agencies have come up with figures for the dollar value of a human life to analyze the costs and benefits of new programs they believe will save lives. A sampling:

According to the Principles of Economics by Gregory Mankiw, economics calculate the

value of a human life by looking "at the risks that people are voluntarily willing to

take and how much they must be paid for taking them".

For example, the decision to work as a contractor in Iraq involved placing a monetary value on

years of extended life. Assuming an annual risk of death of 0.004 and a salary

premium of $30,000 per year over comparable jobs in the United States, contractors in

Iraq are essentially compensated at a rate of $250,000 per statistical year of life. A recent survey of estimates based on occupational risk that found a range from $500,000 to $21 million per statistical life year depending on how dangerous the work is. If someone will accept a 1-in-10,000 chance of death for $500, then the value of life

must be 10,000 times $500, or $5 million.

An example of this kind of analysis was used by the federal Consumer Product Safety

Commission this year:A proposal to make mattresses less flammable was expected to cost the industry $343 million to implement. But, a spokeswoman said, the move was also expected to save 270 people. The commission calculated that each life was worth $5 million, which meant a

benefit of about $1.3 billion.

This total value can also be annualized. The World Health Organization has proposed $108,609 as the value of a disability-adjusted life year, while a recent study by Lee et al using Medicare willingness-to-pay, estimated it as $129,000. Lee notes that this figure compares to a range of $50,000 to $100,000 used in other countries, such as Australia and the UK, which run national health care systems in guiding their coverage decisions.

see: EPA's mortality risk valuation

The fact of the matter is that monetary valuations of human life are a necessary step in triage. However, as Risk and Decision-Making researchers know, individual's valuations of their own and others lives is rarely consistent or logical. For example, many people complain bitterly about automobile or factory pollution, while themselves being one of the largest, willful, and unnecessary sources of pollution:

Environmental Decisions: Easy, Common, Info, or Tough

http://dispatchnie.com/live/export-content/sites/dispatchnie/pdfs/2010InWeather.pdf

Toxic Bodies by Nancy Langston

"Toxic Bodies: Hormone Disruptors and the Legacy of DES" explores why our environment has become saturated with synthetic chemicals that disrupt hormones, and asks what we can do to protect human and environmental health. In this thorough undertaking, Environmental Historian Nancy Langston examines endocrine disruptors as a case study of environmental risk assessment and response. Interesting to compare this book's stance on weight-of-evidence to Our Stolen Future or The Secret History of the War on Cancer by Devra Davis. Compare that to a more formal report by the American Institute for Cancer Research.