Hazard Tree Assessment - Why Is It Important?

Transcription

1 Hazard Tree Assessment - Why Is It Important? 1

2 Dr. George E. Fitzpatrick Professor Emeritus of Environmental Horticulture University of Florida Classes taught: Survey of Arboriculture Palm Production and Culture Environmental Plant Identification and Use Florida Native Plant Landscaping Principles of Composting Technology ISA Certified Arborist Exam Preparation Instructor since 1994

3 Hurricane David August 29, MPH winds for 6 hours 3

4 The Saffir-Simpson Hurricane Wind Scale Wind speed, MPH 1 74 to 95 Very dangerous winds will produce some damage 2 96 to 110 Extremely dangerous winds will cause extensive damage to 130 Devastating damage will occur to 155 Catastrophic damage will occur 5 Over 155 Catastrophic damage will occur Damage Tree branches will snap and fall Trees will be snapped and uprooted Many trees will be snapped or uprooted, blocking numerous roads Most trees will be snapped or uprooted and power poles will break and fall Nearly all trees will be snapped or uprooted and power poles will break and fall 4

5 5

6 6

7 7

8 8

9 Targets are people or property that could be injured, killed, or damaged if the tree fails. 9

10 Crossing branches grow and become rubbing branches. Rubbing branches create broken bark and wood decay and one or both branches fail and fall. 10

11 11

12 12

13 Tree Risk Assessment: The process of evaluating the likelihood that part or all of a tree will fail (fall) and cause damage, injury or death. 13

14 Hazard tree assessment-why is it important? Arborists perform hazard tree assessments to: Enhance public safety Protect workers on the job site Promote tree longevity by predicting and preventing tree structural failure 14

15 Risk Assessment Basics 15

16 Failure potential: The likelihood that an entire tree, or part of a tree, will break and fall within a given period of time. 16

17 Targets: People or property that could be damaged, injured or killed if the tree fails. 17

18 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 18

19 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. 19

20 20

21 Hurricane Wilma October

22 22

23 23

24 24

25 25

26 26

27 27

28 28

29 29

30 30

31 31

32 32

33 33

34 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. 34

35 Tree Inspection 35

36 VTA: A Visual Tree Assessment Involves a thorough, systematic inspection, walking completely around the tree. 36

37 37

38 Visual Tree Assessment (VTA): Is there dieback, gaps or discoloration in the tree s 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? 38

39 Trunk Taper Diameter should decrease as you measure higher up the trunk 39

40 Codominant leaders 40

41 41

42 42

43 Co-dominant leaders are very prone to splitting. 43

44 44

45 It is not a question of If It is a question of When 45

46 Girdling root 46

47 47

48 48

49 Girdling roots press against the root buttress, destroying phloem tissue. The lateral roots that receive nutrients through the destroyed phloem decline and die. 49

50 50

51 51

52 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 52

53 Tree Decay 53

54 Mushrooms at the base of a tree are indicators on decay inside the tree. 54

55 55

56 Indicators of decay Fungal fruiting bodies mushrooms conks brackets Open cavities Visible decayed wood 56

57 Ganoderma conk on cabbage palmetto 57

58 Basal rot can lead to tree failure at the base. 58

59 59

60 60

61 Potential indicators of decay Cracks Seams Bulges Wounds 61

62 Useful tools for tree inspections Air excavation devices Binoculars Listening devices Increment borers Electric drills Resistograph 62

63 Risk Assessment and Management 63

64 Risk Assessment and Management Requires knowledge of both tree biology and structure-function relations in trees All observations, measurements and recommendations must be documented Numeric formulas are available (i.e., Matheny and Clark). 64

65 Two-page form recommended by the ISA for Tree Hazard Evaluation 65

66 The Hazard Rating is the sum of 3 factors: Failure potential (1-4) plus Size of defective part (1-4) plus Target rating (0-4) 66

67 67

68 Failure potential 1= low 2 = medium 3 = high 4 = severe 68

69 Size of defective part 1 = less than 6 inches diameter 2 = 6 to 18 inches diameter 3 = 18 to 30 inches diameter 4 = greater than 30 inches diameter 69

70 Target rating 0 = No target 1 = occasional use 2 = intermittent use 3 = frequent use 4 = constant use 70

71 Hazard Tree Case Studies 71

72 Case Study 1 This tree is a multiple-trunked maple (Acer sp.), which had been growing wild prior to the construction of the house. Construction activities severed most of its large roots. The crown had significant dieback. An irrigated landscape was installed beneath the tree. This tree could fail in several ways: branch failure, one of the trunks could split out, or the entire tree could fall over, especially during high winds. The inspector must determine which of these failure events is most likely to occur during the evaluation period. Upon inspection, the arborist determined that failure of the largest trunk with a 28 inch diameter trunk was most likely. The tree s hazard rating would be: Failure potential: 3 Size of defective part: 3 Target rating: 4 Hazard rating: 10 72

73 Case Study 1 Failure potential: 3 Size of defective part: 3 Target rating: 4 Hazard rating: 10 73

74 Case Study 2 74

75 Case Study 2 Most of the canopy of this sycamore (Plantanus sp.) extended to the south in an open field. The tree had a cavity up the trunk to approximately 20 feet above ground level. The side opposite the cavity opening had several vertical fissures that decreased the trunk s ability to resist twisting in high winds. The trunk had fungal conks (Ganoderma and Daldinia). Testing with an electric drill revealed large areas within the trunk were decayed. Given these defects, failure of the entire tree was highly probable. Since the tree is in an open field, far away, from any activity, there is no target, and therefore no hazard exists. The hazard rating is Failure potential: 4 Size of defective part: 4 Target: 0 Hazard rating: 0 75

76 76

77 Case Study 2 Most of the canopy of this sycamore (Plantanus sp.) extended to the south in an open field. The tree had a cavity up the trunk to approximately 20 feet above ground level. The side opposite the cavity opening had several vertical fissures that decreased the trunk s ability to resist twisting in high winds. The trunk had fungal conks (Ganoderma and Daldinia). Testing with an electric drill revealed large areas within the trunk were decayed. Given these defects, failure of the entire tree was highly probable. Since the tree is in an open field, far away, from any activity, there is no target, and therefore no hazard exists. The hazard rating is Failure potential: 4 Size of defective part: 4 Target: 0 Hazard rating: 0 No hazard 77

78 78

79 Case Study 2, one year later Most of the canopy of this sycamore (Plantanus sp.) extended to the south in an open field. The tree had a cavity up the trunk to approximately 20 feet above ground level. The side opposite the cavity opening had several vertical fissures that decreased the trunk s ability to resist twisting in high winds. The trunk had fungal conks (Ganoderma and Daldinia). Testing with an electric drill revealed large areas within the trunk were decayed. Given these defects, failure of the entire tree was highly probable. Development of an office complex was planned around the tree, at which the tree became potentially hazardous. Since it was a historically significant tree, local ordinance required that the tree be preserved. The hazard rating now is Failure potential: 4 Size of defective part: 4 Target: 4 Hazard rating: 12 Extreme hazard 79

80 Mitigation Options 80

81 Mitigation: The process of reducing risk potential. Mitigation may include: Removing the target Fencing off the area Removal of dead and broken branches Installation of bracing or cabling Lightning protection systems 81

82 Pruning dead and diseased branches and the installation of tree support systems can be options to mitigate risks. 82

83 Liability and Negligence Arborists have a duty of care and are held to higher standards because of their higher level of knowledge and experience. 83

84 Liability and Negligence Negligence is the failure to exercise due care. Causation in fact means that the damage, injury or death can be traced back to a person s action (or inaction). Act of God is an occurrence due to natural causes that could not have been prevented by ordinary skill and foresight. 84

85 All trees pose a risk, some trees more than others. Risk management means that the owner or property manager must decide what level of risk is acceptable. 85

86 86

87 Hazard tree assessment 87

88 Why is it important? 88

89 Hazard tree assessment-why is it important? Arborists perform hazard tree assessments to: Enhance public safety Protect workers on the job site Promote tree longevity by predicting and preventing tree structural failure 89

90 Thank you! 90