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Strengthening our Community Tree Canopy Through Education Module #10: Hazard Tree Evaluation Laura Sanagorski, Environmental Horticulture Extension Faculty.

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Presentation on theme: "Strengthening our Community Tree Canopy Through Education Module #10: Hazard Tree Evaluation Laura Sanagorski, Environmental Horticulture Extension Faculty."— Presentation transcript:

1 Strengthening our Community Tree Canopy Through Education Module #10: Hazard Tree Evaluation Laura Sanagorski, Environmental Horticulture Extension Faculty

2 Strengthening Our Community Tree Canopy 2012 Urban Forestry Series This series is a part of a project titled Strengthening Our Community Tree Canopy Through Education. This project is made possible by a grant through the 2011 National Urban and Community Forestry Grant Program and the Florida Department of Agriculture and Consumer Services, and the Florida Forest Service.

3 Hazard Tree Evaluation

4 Hazard Tree Assessment: The process of evaluating the likelihood that part or all of a tree will fail (fall) and cause damage and/or injury. 4

5 Arborists perform tree risk assessments to: Enhance public safety Protect workers on the job site Promote tree longevity by predicting and preventing tree structural failure 5

6 Risk Assessment Basics 6 Failure potential: The likelihood that an entire tree, or part of a tree, will break and fall within a given period of time. Targets: People or property that could be damaged, injured or killed if the tree fails.

7 Tree stability may be affected by: Construction, grade changes and trenching Removal of adjacent trees that previously served as a wind buffer Replacement of sidewalks and root loss Failure of nearby trees Change in wind dynamics Storms cause most tree failures Either during the storm, Or after the storm as a direct result of damage that occurred because of the storm. 7

8 Tree Inspection A Visual Tree Assessment (VTA) involves a thorough, systematic inspection, walking completely around the tree. 8 Is there dieback, gaps or discoloration in the trees crown? Is the tree leaning? Are individual branches extending beyond the rest of the crown? Does the tree have good tree taper? Are there abnormalities in the trunk, root collar or root zone? Photo: UF George Fitzpatrick Photo: UF George Fitzpatrick Visual Tree Assessment

9 9 Trunk Taper Diameter should decrease as you measure higher up the trunk

10 10 Co-dominant leaders Included bark; little or no connective wood. Photos: UF George Fitzpatrick

11 11 Photo: UF George Fitzpatrick

12 12 Photo: Bill DuMond

13 Common Defects Associated with Tree Failure Codominant stems Included bark Cracks and splits Multiple attachments Cross branching Girdling roots Wounds Decay Cavities Fungal fruiting bodies Bleeding Loose or cracked bark Nesting holes Deadwood Borers, termites ants Leaning tree Overpruned palms Previous failure 13

14 Tree Decay 14 Fungal fruiting bodies, mushroom like structures, can indicate significant decay inside the tree. Basal rot can lead to tree failure at the base. Potential Indicators of Decay Cracks Seams Bulges Wounds Photos: UF George Fitzpatrick

15 Useful tools for tree inspections Air excavation devices Binoculars Listening devices Increment borers Electric drills Resistograph 15

16 Risk Assessment and Management Requires knowledge of both tree biology and structure-function relations in trees All observations, measurements and recommendations should be documented Numeric formulas are available (i.e., Matheny and Clark). 16

17 Two-page form recommended by the ISA for Tree Hazard Evaluation 17

18 18

19 Hazard Rating FAILURE POTENTIAL (1-4) + SIZE OF DEFECTIVE PART (1-4) + TARGET RATING (0-4) ___________________________________________________________________________

20 Hazard Rating – Failure Potential 1 = low 2 = medium 3 = high 4 = severe

21 Hazard Rating – Size of Defective Part 1 = less than 6 inches 2 = 6 to 18 inches 3 = 18 to 30 inches 4 = greater than 30 inches

22 Hazard Rating – Target Rating 0 = No target 1 = occasional use 2 = intermittent use 3 = frequent use 4 = constant use

23 Hazard Tree Case Studies 23

24 The tree in question is a Bael Fruit(Aegle marmelos), that is located in a botanical garden adjacent to a walkway at the main entrance, where a steady flow of pedestrian traffic occurs. The tree possesses numerous codominant trunks with bark inclusion and also has visual signs of decay and cracks at the areas of bark inclusion. Additionally, pruning cuts were made in the past that have not compartmentalized. Beneath one of the codominant trunks is a bench that could be considered a potential target. Furthermore, a hanging basket with a staghorn fern is situated on this particular codominant trunk. Additionally, visitors to the garden should also be considered targets. This tree could potentially experience branch failure from any one of the codominant trunks, especially the one with the excess weight of the fern. Upon inspection, it appeared that this particular branch was most likely to fail As such, the trees hazard rating would be: Failure potential:3 Size of defective part:2 Target rating:3 Hazard rating: 8 Case Study 1 24

25 Failure potential: 3 Size of defective part: 2 Target rating: 3 Hazard rating: 8 Case Study 1 25

26 This large Live Oak (Quercus virginiana), is approximately years old and is 51.5 DBH (diameter at breast height). It is located adjacent to a walkway that leads from a parking lot to the main entrance of a building and receives a fair amount of regular pedestrian traffic. The tree has numerous codominant trunks that are roughly the same diameter and originate low on the tree. There is also bark inclusion present and cracks are forming where the bark is trapped between the trunks. The narrow branch angles on the tree appear to be retaining moisture and could possibly be harboring decay. A number of branches have excessive end weight and there is evidence that a number of pruning cuts and wounds have failed to seal over. Given these defects, this tree has potential of failure from one of the large codominant trunks. Upon inspection, it was determined that a branch with a diameter of approximately posed the greatest threat for failure, though, while highly possible, it is not necessarily imminent. As such, the trees hazard rating would be: Failure potential:3 Size of defective part:3 Target rating:3* Hazard rating: 9 * - Picnic tables formally underneath the oak were removed to reduce the target rating, bringing it from a 4 to a 3. Case Study 2 26

27 Failure potential: 3 Size of defective part: 3 Target rating: 3 Hazard rating: 9 Case Study 2 27

28 Mitigation Options 28

29 Mitigation: The process of reducing risk potential. May include: Removing the target Fencing off the area Removal of dead and broken branches Installation of bracing or cabling Lightning protection systems 29

30 Liability and Negligence Arborists have a duty of care and are held to higher standards because of their higher level of knowledge and experience. 30 Negligence is the failure to exercise due care. Causation in fact means that the damage, injury or death can be traced back to a persons action (or inaction). Act of God is an occurrence due to natural causes that could not have been prevented by ordinary skill and foresight. All landscape trees pose a risk and some trees pose more risk than others. The property owner must decide what level of risk is acceptable. The arborist can assess risk and make recommendations.

31 Strengthening our Community Tree Canopy Through Education Module #10: Hazard Tree Evaluation Laura Sanagorski, Environmental Horticulture Extension Faculty


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