Tree Risk Assessment Mitigation Reports: Tree Removal, Tree Retention?

Summary: Sharon Lilly, Nelda Matheny and E. Thomas Smiley discuss opting for and recording tree removal or tree retention in tree risk assessment mitigation reports.

Tree risk assessment mitigation reports assess tree removal or, preferentially, tree retention; risk tree (right) in park near Tawas City, Iosco County, Lower Peninsula of Michigan: Joseph O'Brien/USDA Forest Service/Bugwood.org, CC BY 3.0 Unported, via Forestry Images

Tree risk assessment mitigation reports are records of the inspections, remedies and reviews of risky trees, according to Tree Risk Assessment: Mitigation and Reporting in the August 2012 issue of Arborist News.

Sharon Lilly of the International Society of Arboriculture, Nelda Matheny of HortScience, Inc., and E. Thomas Smiley of the Bartlett Tree Research Laboratory begin with risk-taking. Master gardeners, master naturalists, tree risk assessors and tree stewards consider tree-based risks regarding the likelihood of tree failure and impact and target-based risks respecting consequences. Target-based thinking drives clients and tree risk assessors to decide immediately upon "the ultimate security of risk elimination based on tree removal" over tree retention options.

Residual risk endures in target-based options since "With tree removal, that residual risk is brought to near zero; however, even stumps can pose some residual risk."

Tree-based thinking finds "possibilities for retaining trees when practicable" since "Trees offer many benefits," such as anchoring soils against erosion, releasing oxygen and removing carbon dioxide.

The "preventive and remedial" mitigation process gets the "likelihood of failure or the likelihood of impact" and their consequences to a level "acceptable to the client." Tree retention mitigation heads toward drainage systems, lightning protection and structural support brace rods, cables, guys and props to reduce wet soil-, storm- and wind-induced failures. Crown-raising, pollarding, reduction pruning, thinning and tree growth regulators increase wind dissipation and transfer while relocating, rerouting or restricting mobile and movable targets inhibits risky access.

Tree risk assessment mitigation reports juggle information, such as residual risks and risk ratings of extreme-risk, high-risk, moderate-risk or low-risk, for tree removal and retention options.

The risk ratings keyed from inspections into tree risk assessment mitigation reports keep work priorities on schedule since extreme-risk trees are mitigated "as soon as possible." They lead to mitigating high-risk trees "as soon as it is practical" and moderate- and low-risk trees whenever pruning cycles and work budgets and schedules converge.

Verbal, videographic, work order or written-up report manages one-time or repeated progression from inspection to intervention, re-inspection and re-intervention for tree removal or tree retention. It notes assessment date and assessor name, inspection level as limited visual or basic or advanced, scope of work, site factors and tree identification and location. It operates as detailed documentation of response growth, storm patterns, structural defects, target mobility and occupancy rates and tree failure and site impact likelihood and consequences.

Tree risk assessment mitigation reports protect "both tree risk assessor and client from misunderstandings" by providing information on residual risks and limitations on inspections and inspectors.

"[U]ncertainties related to trees and the loads to which they are subjected" qualify as limitations on assessments since "scientific study of tree failure is relatively young." Inspectors investigating tree removal and tree retention options reveal as limitations on performance anecdotal information, hidden defects, inaccessible sites, nascent methodology, seasonal pests and unpredictable winds. Limitations suggest inspection intervals of eight to 16 months, one to two years and three to five years for pest-prone, high-risk and low- to moderate-risk trees.

Assessment, mitigation, re-inspection and re-intervention take assessors and clients close to de-mystifying how trees avoid failure and what wind directions and speeds cause trees to fail.

Measuring a tree's vitality with an electrical conductivity meter is helpful in tree risk assessment retention or removal: USDA Forest Service-Northeastern Area/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 mitigation reports assess tree removal or, preferentially, tree retention; risk tree in park near Tawas City, Iosco County, Lower Peninsula of Michigan: Joseph O'Brien/USDA Forest Service/Bugwood.org, CC BY 3.0 United States, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=5030027

Measuring a tree's vitality with an electrical conductivity meter is helpful in tree risk assessment retention or removal: USDA Forest Service-Northeastern Area/USDA Forest Service/Bugwood.org, CC BY 3.0 United States, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=1407063

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. 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. August 2012. "Tree Risk Assessment: Mitigation and Reporting." Arborist News 21(4): 14-18.
Available @ http://viewer.epaperflip.com/Viewer.aspx?docid=de6602f7-b34e-413f-b53b-a2bd009f8b0d#?page=14