Tree Adaptive Growth: Tree Risk Assessment of Tree Failure, Tree Strength

Summary: Sharon Lilly, Nelda Maheny and E. Thomas Smiley use tree risk assessment to link tree failure to structural defect or tree strength to tree adaptive growth.

Tree risk assessment considers tree damages in the context of tree failure and/or strength; lightning damage to loblolly pine (Pinus taeda): Paul A. Mistretta/USDA Forest Service/Bugwood.org, CC BY 3.0 United States, via Forestry Images

Tree adaptive growth accounts for tree survival of stress, according to Tree Risk Assessment: Structural Defects and Conditions That Affect the Likelihood of Failure in the October 2012 issue of Arborist News.

Sharon Lilly of the International Society of Arboriculture, Nelda Matheny of HortScience, Inc., and E. Thomas Smiley of Bartlett Tree Research Laboratory begin with tree failure. Tree failures can occur during gentle weather because of structural defects compromising tree strength and during severe events because of extreme overloads compromising healthy tree structures. Tree risk assessors designate as structural defects "injuries, growth patterns, decay, or other conditions that reduce the tree's structural strength" and sometimes result in tree failure.

Site, tree and weather conditions explain whether the potential for failure is imminent, improbable even during extreme events or possible or probable under prevailing area conditions.

Adventitious, broken, co-dominant, decaying, hanging, overextended, thicket-like and V-junctioned branches and branch cracks, ribs and seams furnish high-profile examples of branches that tree risk assessment flags.

No or less holding wood gets formed around partial, severed or weak branch attachments to stems, whose dominance requires diameters twice those of the largest branches. Co-dominant branches, near-sized branches and stems and same-sized stems have embedded, included, shared bark that helps cracks to form and hinders the strength of holding wood. Co-dominance implicates mutual branch and stem bark whose vulnerability increases when tree height is compromised by crown bows and trunk leans off-center, respectively downward and sideward.

Co-dominance joins with branches overextended sideward or upward "outside the normal crown area" to jump-start tree failure from overloads or tree strength through tree adaptive growth.

Leafy crowns and woody roots keep branches, stems and trunks balanced by tree adaptive growth and tree strength and imbalanced by site conditions and structural defects.

Live crown ratios let the "vertical extent (height) of the live crown," as leaf- or needle-producing areas, "to the height of the whole tree" be calculated. They measure healthily at "greater than 65 percent," when the upper 65 percent of the tree has live branches," and precariously at "less than 33 percent." Lightning, mechanical injury, overcrowded groves, repeated defoliation, root problems, soil imbalances, transplant shock, vascular diseases and severe weather number among crown dieback and precarious ratio triggers.

Tree risk assessment observes crown- and root-impacting tree failure scenarios from such ground- and underground-related problems as mechanical injury, moisture extremes, nutrient deficiencies and soil compaction.

Division of tree height by trunk diameter provides the degree of taper, or slenderness, from roots to crown, with critical values varying "from 50:1 to 90:1."

Taper never quantifies tree failure or tree strength in tree risk assessment of palms or of "undisturbed forested" trees "less prone to falling" and to wind. Measurement of its basal diameters, when expanded by fused buttress roots and wide root flares, always reveals tree adaptive growth to root anchorage problems in soil. Diminished openings and expanded bases signal roots respectively compromised by or reactive to carpenter ants, decayed openings, disturbed soils, fungal fruiting bodies, restricted spaces, termites and wounds.

Every part of the tree, from above-ground shoots to below-ground roots, tells a survival story to master gardeners, master naturalists, tree risk assessors and tree stewards.

Tree risk assessment considers tree damages and identifies any adaptive growth as indicative of tree failure and/or strength; illustration of compartmentalization of decay (CODIT): Paul A. Mistretta/USDA Forest Service/Bugwood.org., CC BY 3.0 United States, via Forestry Images

Acknowledgment

My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet;
University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:

Tree risk assessment considers tree damages in the context of tree failure and/or strength; lightning damage to loblolly pine (Pinus taeda): Paul A. Mistretta/USDA Forest Service/Bugwood.org, CC BY 3.0 United States, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=1505060

Tree risk assessment considers tree damages and identifies any adaptive growth as indicative of tree failure and/or strength; illustration of compartmentalization of decay (CODIT): Paul A. Mistretta/USDA Forest Service/Bugwood.org., CC BY 3.0 United States, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=1505081

For further information:

Gilman, Ed. 2011. An Illustrated Guide to Pruning. Third Edition. Boston MA: Cengage.

Hayes, Ed. 2001. Evaluating Tree Defects. Revised, Special Edition. Rochester MN: Safe Trees.

Marriner, Derdriu. 11 August 2012. “Tree Risk Assessment Mitigation Reports: Tree Removal, Tree Retention?” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2012/08/tree-risk-assessment-mitigation-reports.html

Marriner, Derdriu. 16 June 2012. “Internally Stressed, Response Growing, Wind Loaded Tree Strength.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2012/06/internally-stressed-response-growing.html

Marriner, Derdriu. 14 April 2012. “Three Tree Risk Assessment Levels: Limited Visual, Basic and Advanced.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2012/04/three-tree-risk-assessment-levels.html

Marriner, Derdriu. 19 February 2012. “Qualitative Tree Risk Assessment: Risk Ratings for Targets and Trees.” Earth and Space News. Sunday.
Available @ https://earth-and-space-news.blogspot.com/2012/02/qualitative-tree-risk-assessment-risk.html

Marriner, Derdriu. 18 February 2012. “Qualitative Tree Risk Assessment: Falling Trees Impacting Targets.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2012/02/qualitative-tree-risk-assessment.html

Marriner, Derdriu. 10 December 2011. “Tree Risk Assessment: Tree Failures From Defects and From Wind Loads.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/12/tree-risk-assessment-tree-failures-from.html

Marriner, Derdriu. 15 October 2011. “Five Tree Felling Plan Steps for Successful Removals and Worker Safety.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/10/five-tree-felling-plan-steps-for.html

Marriner, Derdriu. 13 August 2011. “Natives and Non-Natives as Successfully Urbanized Plant Species.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/08/natives-and-non-natives-as-successfully.html

Marriner, Derdriu. 11 June 2011. “Tree Ring Patterns for Ecosystem Ages, Dates, Health and Stress.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/06/tree-ring-patterns-for-ecosystem-ages.html

Marriner, Derdriu. 9 April 2011. “Benignly Ugly Tree Disorders: Oak Galls, Powdery Mildew, Sooty Mold, Tar Spot.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/04/benignly-ugly-tree-disorders-oak-galls.html

Marriner, Derdriu. 12 February 2011. “Tree Load Can Turn Tree Health Into Tree Failure or Tree Fatigue.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2011/02/tree-load-can-turn-tree-health-into.html

Marriner, Derdriu. 11 December 2010. “Tree Electrical Safety Knowledge, Precautions, Risks and Standards.” Earth and Space News. Saturday.
Available @ https://earth-and-space-news.blogspot.com/2010/12/tree-electrical-safety-knowledge.html

Smiley, E. Thomas; Matheny, Nelda; and Lilly, Sharon. October 2012. "Tree Risk Assessment: Structural Defects and Conditions That Affect the Likelihood of Failure." Arborist News 21(5): 16-22.
Available @ http://viewer.epaperflip.com/Viewer.aspx?docid=995fc5a5-3425-427c-b937-a2a70102b0a7#?page=16