Technical tree inspection

Transcription

1 Technical tree inspection Dipl.-Phys. Frank Rinn, Heidelberg, Germany

2 2008 TECHNICAL INSPECTION OF TREES 2 / 148 Introduction....3 Urban green...3 Inspection, assessment, examination, evaluation Successful trees....5 Pre-requisites...6 Load to trees and other stress factors...7 Wood anatomy, tree biology and mechanics Wood anatomy Decay Some typical tree growth symptoms Tree failure Technical methods Height over diameter ratio Drill resistance measurements Stress wave tomography Wind load analysis Error calculation in tree assessment Pulling tests and safety calculations Application examples: expert reports on trees Final conclusions

3 2008 TECHNICAL INSPECTION OF TREES 3 / 148 Introduction Urban green Urban green has more positive effects than just making cities looking nice. Urban trees positively influence micro-climate, filter dust and air pollution, provide sun and wind shadow. And they have a positive influence on economic value of shopping and housing areas too. Yet, urban trees have to stand a lot of stresses. Nature does not like air pollution and does not need crown cutting. But urban green has to be adapted to boundary conditions of urban life style, including the needs of buildings and traffic. However, the most dangerous stresses to urban trees are affecting their roots. Urban stress factors accelerate typical aging effects of trees, such as decay in stem and roots. Stems can break, branches can be lost or trees fall over. Therefore urban trees have to be inspected regularly in order to identify hazardous trees and to minimize risks.

4 2008 TECHNICAL INSPECTION OF TREES 4 / 148 Inspection, assessment, examination, evaluation Urban tree inspection is normally done visual - mainly based on knowledge from more than 100 years of forestry and arboricultural research, enriched by modern approaches better understand the body language of trees. Depending on tradition, laws, and standards, in some countries there is a clear line between visual inspection and technical examination of trees. In Germany, for example, all urban trees should be inspected visually (old trees at least one time a year). If there is any doubt about safety, these potentially dangerous trees should be tested technically. To distinguish the different procedures, technical inspection is called examination. Because evaluation of the same tree can be very different by different experts, insurance companies and judges more and more ask for neutral technical evidence rather than subjective opinions.

5 2008 TECHNICAL INSPECTION OF TREES 5 / 148 Successful trees Structure, size and functional capabilities of trees have overcome various difficult climatic periods and diverse local conditions throughout the centennials. Thus trees can be called biologically and evolutionary successful creatures of nature. They obviously have developed successful concepts of how to deal with difficult surrounding conditions. They seem to know how to react to external stress factors limiting their possibilities to develop and grow. Otherwise they would have been diminished in the evolutionary process by other plants. And in fact, we find urban trees more than 100 years old even in cities strongly destroyed several times by war. Trees from high altitude mountain areas are other examples for being able to survive unfriendly climate and even severe mechanical damages. The first step of learning how to inspect trees therefore is to understand their concept of growth and of repair mechanisms to compensate internal or external stress factors.

6 2008 TECHNICAL INSPECTION OF TREES 6 / 148 Pre-requisites Proper technical tree inspection requires deep knowledge about! wood anatomy and tree biology! wood mechanics and wood physics! wind load and other stress factors! limitations and possibilities of technical methods! laws and standards. The formal price of an inspection device is mostly less than the correspondingly required investment into education, to learn how to apply the system, how to interpret and evaluate the results.

7 2008 TECHNICAL INSPECTION OF TREES 7 / 148 Load to trees and other stress factors Loads First of all the tree crown is a load to the stem. Big crowns can weight 20 tons or even more. As long as the stem is vertically upright, it can carry big loads. Lengthwise compression strength of wood is quite high. Theoretically, an oak stem without any defects 1 and 1 meter diameter can carry more than tons of vertical load. However, usually the main load a tree has to carry, is wind load. 1 Assuming compression strength of grren wood of 20N/mm², cross section area of 3.14*0.5*0.5m² ( 0,8m²)

8 2008 TECHNICAL INSPECTION OF TREES 8 / 148 Wind load Static load to a single tree F = 0.5 * A * Cw * v² * ñ Example: F = 0.5 * 40m² * 0.5 * (30m/s)² * 1.25kg/m³ kgm/s² = 11kN 1.1to Variable Measure Depending on v wind speed Time, height above ground, local stand topology,... A crown area Wind direction, foliage, wind speed, temperature,... Cw drag coefficient Tree species, foliage, wind speed, temperature,... ñ air density Temperature, altitude,... Porosity? + Dynamics? + Precision? + Swaying? + Torsion? + Damping? + Errors? => wind load calculation of urban trees contains many uncertainties to be specified!

9 2008 TECHNICAL INSPECTION OF TREES 9 / 148 Other urban stress factors Although urban climate is often influenced by air pollution, this is not the main stress factor affecting trees. Most urban tree problems are coming from other origins:! wrong tree architecture from nursery(co-dominant stems and other potential defects)! wrong treatment / missing preparation in nurseries for urban tree requirements! wrong planting procedure (small place, un-adequate soil,...)! wrong pruning! root cutting by ground / soil works! stem damage (by car or work accidents, for example) Most of these stress factors can be re-constructed by tree ring analysis (except for tropics)

10 2008 TECHNICAL INSPECTION OF TREES 10 / 148 Wood anatomy, tree biology and mechanics! We distinguish between three major species groups of similar wood anatomical properties " conifers " ring porous " diffuse porous! Trees within these groups often react quite similar to external load and stress factors.

11 2008 TECHNICAL INSPECTION OF TREES 11 / 148 Wood anatomy

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14 2008 TECHNICAL INSPECTION OF TREES 14 / 148 Age trend Decreasing ring width with tree age is not automatically correlated to decreasing vitality of the tree.

15 2008 TECHNICAL INSPECTION OF TREES 15 / 148 Density trends Conifers, ring porous, diffuse porous

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17 2008 TECHNICAL INSPECTION OF TREES 17 / 148 Tree growth genetics, biology, soil, stand, competition, climate, weather determine the amount of possible wood growth determines local distribution of growth: where the tree builds up his new wood mechanical stress on the tree surface

18 2008 TECHNICAL INSPECTION OF TREES 18 / 148 Compression wood Conifer trees react against static mechanical stress.

19 2008 TECHNICAL INSPECTION OF TREES 19 / 148 Typical reaction wood (General overview, may be different in individual cases depending on conditions) Tree group Load Static Dynamic Conifer trees Broad leave trees Compression wood Tension wood mature trees: broad rings on compression side Bigger tree rings (low wood quality) In extreme cases: spiral growth.? Bigger tree rings? (still subject to research)

20 2008 TECHNICAL INSPECTION OF TREES 20 / 148 Natural tree design?! Each structure first breaks on its weakest point ( notches ).! Trees try to avoid notches (= points of maximum surface stresses).! Trees accept higher stresses in roots and branches but not on the trunk.! Safety factor of tree design is about ~4.5 (Mattheck)

21 2008 TECHNICAL INSPECTION OF TREES 21 / 148! Because the stem is the most important part of the connection between roots and crown, the repair growth speed is maximum there.! The repair growth can be simulated mathematically: it follows the stress line. The higher the mechanical stress (compression or tension), the faster the growth [as long as the tree is able to do so].

22 2008 TECHNICAL INSPECTION OF TREES 22 / 148 Adaptive growth! The cambium growth request depends on local stress.! Contact to stiff materials cause compression stress.

23 2008 TECHNICAL INSPECTION OF TREES 23 / 148 Decay! Fungal decay is a natural process, necessary for re-cycling wood for new growth!! Reasons / origins of decay in urban trees: " roots (soil works) " stem base (direct damages) " branches (wind or cutting)! Different tree species react different to decay due to their possibilities in compartimentalization (Shigo). (Shigo 1985)

24 2008 TECHNICAL INSPECTION OF TREES 24 / 148! Root based fungi often do not affect the stem but totally destroy the mechanic root system, without weakening vitality correspondingly.! Points to be inspected technically depend on " tree species " fungus " origin of injury " local stand conditions (Shigo 1985)

25 2008 TECHNICAL INSPECTION OF TREES 25 / 148 Some typical tree growth symptoms! Reactions to decay are mostly reactions to stress.! The natural shape of tree stems is mostly round or regular (there are some exceptions especially in the tropics).! Irregular forms mostly are a sign for decay.

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27 2008 TECHNICAL INSPECTION OF TREES 27 / 148 Elliptical growth deviations from a circle mostly indicate internal decay.

28 2008 TECHNICAL INSPECTION OF TREES 28 / 148! The cambium reacts to (internal) decay, as soon as the mechanical stress is significantly higher and if the tree is vital enough to do so.! As long as the decay only affects parts of the tree, that are not required for stability, there is no visible outside symptom on the tree s shape.! Thus trees can be decayed without visual symptoms because of different reasons!

29 2008 TECHNICAL INSPECTION OF TREES 29 / 148! If you see a tree with obvious decay but no reaction wood, the reason can be " the tree is not any more vital enough to react and to build compensatory wood (you can check this by looking into the crown and measuring shoot length) o r " the decay area is small and not dangerous for stability o r " the decay is brown or wet rot in early stages, only affecting bending strength but not density and stiffness (dangerous!). => Technical inspection required!

30 2008 TECHNICAL INSPECTION OF TREES 30 / 148! Such an early stage of brown rot can reduce density and stiffness by 10% and at the same time bending strength by about 90% (Wilcox 1978).! The cambium can not recognize this defect because it observes stiffness. Bending strength can only be observed by breaking the tree or branch until failure.! Extension of early stages of such decay patterns can only be detected technically.! If you find brown rot fungi at a tree, be careful evaluating the tree without technical assistance!

31 2008 TECHNICAL INSPECTION OF TREES 31 / 148 Tree failure Why and when do trees break or fall over? (Mattheck & Bethge 2004)

32 2008 TECHNICAL INSPECTION OF TREES 32 / 148 Trees are designed to withstand wind until approx. 100km/h:

33 2008 TECHNICAL INSPECTION OF TREES 33 / 148 Vogel 1996 (Eucalyptus paniculata, Lavers 1983)

34 2008 TECHNICAL INSPECTION OF TREES 34 / 148 Skatter & Kucera 2000: Data that were originally collected to study systematic asymmetries in the canopies of Scotch pines (Pinus sylvestris) were used as input in previously developed models. These models predict whether a tree will break due to bending loads or torsional loads during critical wind exposure. Data from four pine stands were used in the study two lowland stands and two mountainous stands. For each of the stands there were large amounts of both categories of trees: those predicted to break due to bending and those predicted to undergo torsional failure. Moreover, there was no significant difference between any of the stands when it came to the distribution of predicted failure modes. These two facts suggest that the risk of bending failure and torsion failure is balanced so that neither is more likely than the other. The fact that torsion may be as critical as bending is a new finding. (For. Ecol. Manage :97 103)

35 2008 TECHNICAL INSPECTION OF TREES 35 / 148 Numerical failure criteria?! How hollow is a tree allowed to be?! How many roots can be missing until the tree in un-safe?! There are some numerical approaches helping us to understand " tree stability " uprooting safety

36 2008 TECHNICAL INSPECTION OF TREES 36 / 148 The more hollow a tree is, the higher the risk of bending breakage:

37 2008 TECHNICAL INSPECTION OF TREES 37 / 148 Statistical approach: natural failures in forests (Mattheck 1993):

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40 2008 TECHNICAL INSPECTION OF TREES 40 / 148 Conclusion! Trees react to decay " by compensatory growth (adaptive growth) " as long as they are vital enough! As soon as the residual intact wall is less then 1/3 of the radius " the tree is not automatically hazardous, but " breakage safety of the fully crowned tree drops down " risk should be assessed " and probably load reduced! Determination of residual intact wall thickness can be complicated, often technical methods are required.

41 2008 TECHNICAL INSPECTION OF TREES 41 / 148 Technical methods There are many different physical principles that can be used to inspect trees:! mechanical (most commonly used) " sound / stress waves: knocking, stress wave timing, ultra-sound " drilling / pin-pushing, increment coring, resistance drilling " inclination and elongation (observing under wind-load and/or pulling)! electrical: 2-point or multipoint impedance (electrical resistance)! electromagnetic: radar, x-ray, nuclear magnetic resonance, thermography Most popular methods in urban tree care: drill resistance and stress-wave timing.

42 2008 TECHNICAL INSPECTION OF TREES 42 / 148 Measuring the tree?! Each measurement is related to errors " Using even simple technical equipment is always related to encounter errors " When giving numerical results, an error evaluation should be included! The more complex the numerical approach, " the more errors add up " the more difficult to explain the result to the customer

43 2008 TECHNICAL INSPECTION OF TREES 43 / 148 Height over diameter ratio! From forestry, it is well known and accepted, that slenderness is a valid criteria for characterizing storm resistance of dens forest stands.! It is assumed that trees within stands are of higher risk, as soon as tree height / trunc diameter > 70

44 2008 TECHNICAL INSPECTION OF TREES 44 / 148 For solitary trees, this ratio shall be about 50. Trees with h/d>50 are assumed to be of higher risk for storm breakage of the stem. (Mattheck 2001)

45 2008 TECHNICAL INSPECTION OF TREES 45 / 148 (Mattheck 2001)

46 2008 TECHNICAL INSPECTION OF TREES 46 / 148 Increment coring Often done for tree ring analysis.

47 2008 TECHNICAL INSPECTION OF TREES 47 / 148 Climate reconstruction is often based on tree ring density analysis by of increment cores

48 2008 TECHNICAL INSPECTION OF TREES 48 / 148 using x-ray, optical or other scanning techniques.

49 2008 TECHNICAL INSPECTION OF TREES 49 / 148 Drill resistance measurements Continuous measurement of penetration resistance of thin needles entering the wood until ~1.5m depth. Kamm & Voß 1984 Rinn & FEIN 1987 Kipp 1990

50 2008 TECHNICAL INSPECTION OF TREES 50 / 148 History and origin of the RESISTOGRAPH drill-resistance method 1970 Pin-penetration depth ~ wood density (Liechtenstein) 1972 In-sizing of wooden utility poles => needle penetration resistance (Germany) 1973 Resistance drilling by torque-measurement of particle boards (Germany) 1978 Recording soil penetrometer (USA) 1983 Recording motor power as measure of mechanical resistance (Japan) 1984 Spring-loaded recording of needle drill resistance with scratch pin on wax paper 1985 Needle drill resistance by motor power (Germany) 1986 Diploma thesis: tree ring analysis by resistance drilling (RINN, Heidelberg, Germany) 1987 First portable series of drills to inspect trees and timber (Rinn & FEIN, Germany) 1990 Patent on electronic drill resistance measurements (Rinn) and needle geometry 1993 RESISTOGRAPH as registered trademark (mw. in more than 30 countries, Rinn)

51 2008 TECHNICAL INSPECTION OF TREES 51 / 148 The real story! To make wooden utility poles more resistant against fungi, a German engineering company started 1972 pushing thin needles into the wood in order to get the chemical preservatives deeper in. Two retiring engineers of that company got the idea as a gift for being applied as a patent (although it was not their personal idea). The patent was later rejected by the German Patent Supreme Court due to older publications describing similar devices (from Japan). In addition, several other experts contributed ideas how to encounter the penetration resistance of needles, pins or borers into wood.! , in my physics diploma thesis at Heidelberg University, I checked if it is possible to obtain information about tree-ring density variations based on the patent application. It did not work in oak due to specific wood anatomical features but in conifers. The profiles clearly revealed tree rings in conifers and showed typical differences between intact and decayed wood in forth and backward drillings.! All subsequently shown graphs, correlations and statements are valid only for these electronically regulated, electronic and linear recording drill resistance devices!

52 2008 TECHNICAL INSPECTION OF TREES 52 / 148 Technical basics An electric motor drives a fast rotating needle into wood. The mechanical torque at the needle s tip is proportional to wood density if the needle s tip has a specific geometry. The power consumption is proportional to the torque, if recorded electronically (linear axis!). If these conditions are fulfilled, the measured value can reliably be correlated to material properties (such as wood density)!

53 2008 TECHNICAL INSPECTION OF TREES 53 / 148 Typical profiles in intact conifer and oak wood:

54 2008 TECHNICAL INSPECTION OF TREES 54 / 148 In conifers, compression wood can be identified by a broader latewood band:

55 2008 TECHNICAL INSPECTION OF TREES 55 / 148 Tree rings of diffuse porous species can be clearly visible (Fagus) but can be invisible as well:

56 2008 TECHNICAL INSPECTION OF TREES 56 / 148 Poplar:

57 2008 TECHNICAL INSPECTION OF TREES 57 / 148 Platanus:

58 2008 TECHNICAL INSPECTION OF TREES 58 / 148 Tilia:

59 2008 TECHNICAL INSPECTION OF TREES 59 / 148 Tree-ring structure and ring width age-trend determine stem trends of density:

60 2008 TECHNICAL INSPECTION OF TREES 60 / 148 Typical profile from oak with high density in the center:

61 2008 TECHNICAL INSPECTION OF TREES 61 / 148 Complete drilling through beech (Fagus) with a nearly constant density profile:

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65 2008 TECHNICAL INSPECTION OF TREES 65 / 148 Tree rings can only be identified in the resistance profile if the needle penetrates the borders perpendicular!

66 2008 TECHNICAL INSPECTION OF TREES 66 / 148 Defect and decay detection and evaluation in resistance profiles! Defects are not always related to decay: " included bark between co-dominant stems! Depending on drilling point, the profile may appear as showing defect but " it can be soil " empty space between roots! Thus it is important to " first visually check the tree " then evaluate the best position to drill " then drill and cross-check the result with visual symptoms!

67 2008 TECHNICAL INSPECTION OF TREES 67 / 148 Included bark

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69 2008 TECHNICAL INSPECTION OF TREES 69 / 148 Finding strong decay is mostly easy:

70 2008 TECHNICAL INSPECTION OF TREES 70 / 148 Decay my be small and missed by drilling.

71 2008 TECHNICAL INSPECTION OF TREES 71 / 148 Ring shake (fungal decay in one early wood band only), only visible by small depressions:

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73 2008 TECHNICAL INSPECTION OF TREES 73 / 148 Strong decay is easy to identify but a low profile does not automatically mean hollow :

74 2008 TECHNICAL INSPECTION OF TREES 74 / 148 Compensatory growth is not always easy to evaluate (even in conifers):

75 2008 TECHNICAL INSPECTION OF TREES 75 / 148 Decay is not always concentric

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77 2008 TECHNICAL INSPECTION OF TREES 77 / 148 The transition from intact to decay tells us something about compartimentalization: Trends of decay expansion can be estimated but, here we found two different types of transition in the same stem disk! Compartimentalization may work on one spot but not on another one!

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81 2008 TECHNICAL INSPECTION OF TREES 81 / 148 Difficult transition from intact to decay in early stages of brown rot and soft rot.

82 2008 TECHNICAL INSPECTION OF TREES 82 / 148! A tree without defined residual wall thickness.! Drilling does not help evaluating safety of such a cross section.! Many drillings would be required to obtain the real situation.

83 2008 TECHNICAL INSPECTION OF TREES 83 / 148 Residual wall thickness?

84 2008 TECHNICAL INSPECTION OF TREES 84 / 148 Drilling provides information valid for one spot! Where and how often should we drill?

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86 2008 TECHNICAL INSPECTION OF TREES 86 / 148 Decay by drilling?! Since 1987 I am drilling standing trees.! Until now we did not find any case where decay started by drilling or extended significantly.! In most cases, there is a dis-colouration around the drilling hole. (Mattheck&Weber 2000) =>! Resistance drilling is not non-destructive! Therefore, we should drill " only if necessary and only on the optimum spot " and we should extract as much information from the profiles as possible.! Therefore many people now use stress wave tomography before drilling.

87 2008 TECHNICAL INSPECTION OF TREES 87 / 148 Stress wave tomography!... using chains of electronically independent sensors was developed in the 1990ies in order to make " tree and timber inspection less destructive and " deliver a more descriptive presentation of the internal state of the tree.! The first publication describing combined stress wave tomography in wood came out in May 1999 (Rinn: international Patent in EU and USA on stress wave and electrical impedance tomography).! Application is nearly non-destructive but due to physical properties of the method(s) it does primarily not show the internal state of a tree!! => Understanding wood anatomical and physical properties is one of the basic prerequisites for a proper application of these technical tree inspection methods and for a reliable interpretation and evaluation of the results.

88 2008 TECHNICAL INSPECTION OF TREES 88 / 148 Basics of stress wave tomography! First put the sensors around the tree " The distance between and the total number of sensors is free but should reflect the geometry of the cross section.! Then note their position in a table.! Select height, location and tree species.! Connect all the sensors by a cable.! Knock on each sensor several times.! That s it.

89 2008 TECHNICAL INSPECTION OF TREES 89 / 148 Measurement principle Speed of impulse = length of path / time of flight Stress wave tomographs only measure time of flight. Travel path and speed of the impulse are unknown! There is no solution for the equation!

90 2008 TECHNICAL INSPECTION OF TREES 90 / 148! The computer program re-constructs the inner situation of the measured cross-section based on " scientific knowledge and " experience (of the manufacturer).! Thus there are sometimes big differences between the different products!

91 2008 TECHNICAL INSPECTION OF TREES 91 / 148 Stress wave tomography is! using only short impact pulses! no ultrasound!! only encounters the travel time of the beginning of the first incoming wave!! not distinguishing between longitudinal and transverse waves! strongly depending on wood anatomical influences by different species, such as: " age trend " species specific properties " anisotropy! thus depending on climate, stand, wheather, season,...

92 2008 TECHNICAL INSPECTION OF TREES 92 / 148 Typical travel paths in wood with defects

93 2008 TECHNICAL INSPECTION OF TREES 93 / 148 Example tomograms Intact oak

94 2008 TECHNICAL INSPECTION OF TREES 94 / 148 Intact spruce

95 2008 TECHNICAL INSPECTION OF TREES 95 / 148 Extended decay in horse chestnut

96 2008 TECHNICAL INSPECTION OF TREES 96 / 148 Compartimentalized decay

97 2008 TECHNICAL INSPECTION OF TREES 97 / 148 Spatial resolution and precision?

98 2008 TECHNICAL INSPECTION OF TREES 98 / 148 No resolution defined in decay parts!

99 2008 TECHNICAL INSPECTION OF TREES 99 / 148 Colour games? Subjective impression of colour scale influences evaluation!

100 2008 TECHNICAL INSPECTION OF TREES 100 / 148 Do stress wave tomograms of trees reveal wood condition?! Generally NO!... (luckily!)! Sometimes YES!...(helpfully!)

101 2008 TECHNICAL INSPECTION OF TREES 101 / 148 Example

102 2008 TECHNICAL INSPECTION OF TREES 102 / 148 Residual wall thickness from stress wave tomograms? Sometimes YES, often NO!

103 2008 TECHNICAL INSPECTION OF TREES 103 / 148 Comparison with RESISTOGRAPH profile Stress-wave tomography of Kapok-tree at HortPark, Singapur Resistograph drilling at sensor #7.

104 2008 TECHNICAL INSPECTION OF TREES 104 / 148 Conclusion Stress wave tomography mainly reveals mechanical compactness of the wood in the cross-section. This information is more important for stability evaluation than wood condition because it correlates to moment of inertia (and subsequently strength of the cross section)! Therefore we can calculate the most dangerous wind direction from relative determination of moment of inertia of the cross section!

105 2008 TECHNICAL INSPECTION OF TREES 105 / 148 Root analysis by stress waves (in use in expert reports since 2004)! Finding roots " to prevent damages by constructions " to check for damages by construction works afterwards! Identifying the tree who is " responsible for damages to footpaths or walls or tubes! Estimating anchorage weight for stability evaluation.

106 2008 TECHNICAL INSPECTION OF TREES 106 / 148 Simple application

107 2008 TECHNICAL INSPECTION OF TREES 107 / 148 Typical results

108 2008 TECHNICAL INSPECTION OF TREES 108 / of 16 trees (similar stand conditions but different root distribution)

109 2008 TECHNICAL INSPECTION OF TREES 109 / 148 Here we had to check to which tree the roots belong that destroy the footpath.

110 2008 TECHNICAL INSPECTION OF TREES 110 / 148 Building permit? (red=planned building size, green = canopy area of trees)

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113 2008 TECHNICAL INSPECTION OF TREES 113 / 148 Wind load analysis! During the last years some experts are trying " to calculate real wind load to the tree and " to combine pulling tests in order " to calculate tree safety.! A closer look to the formulas and procedures inhibits " systematic errors " basic restrictions " and potential reliability.! First we have to evaluate real wind load, then material properties.

114 2008 TECHNICAL INSPECTION OF TREES 114 / 148 Vertical wind profile

115 2008 TECHNICAL INSPECTION OF TREES 115 / 148 Drag coefficient of trees Varies with wind speed. (Ruck 2008)

116 2008 TECHNICAL INSPECTION OF TREES 116 / 148 Drag coefficient of trees Varies between species (Ruck 2008)

117 2008 TECHNICAL INSPECTION OF TREES 117 / 148 Turbulence around a tree (Ruck 2008)

118 2008 TECHNICAL INSPECTION OF TREES 118 / 148 (Ruck 2008)

119 2008 TECHNICAL INSPECTION OF TREES 119 / 148 (Ruck 2008)

120 2008 TECHNICAL INSPECTION OF TREES 120 / 148 Stand effect on wind-load (Ruck 2008)

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124 2008 TECHNICAL INSPECTION OF TREES 124 / 148 Structured thinning at the forest edge helps prohibiting wind breakage.

125 2008 TECHNICAL INSPECTION OF TREES 125 / 148 Dynamic swaying of crown parts dissipate energy and helps prohibiting failure. Cutting branches can even increase total wind load although crown mass and wind sail area are reduced! James 2003

126 2008 TECHNICAL INSPECTION OF TREES 126 / 148 Error calculation in tree assessment Errors affect all measurements Tree diameter

127 2008 TECHNICAL INSPECTION OF TREES 127 / 148 Tree height

128 2008 TECHNICAL INSPECTION OF TREES 128 / 148 Residual intact wall t + r 30-50% => (t/r) >> 50% => be careful evaluating a tree by one measurement only!

129 2008 TECHNICAL INSPECTION OF TREES 129 / 148 Example measurement of one tree by 15 experts:

130 2008 TECHNICAL INSPECTION OF TREES 130 / 148 Error calculation and cumulation

131 2008 TECHNICAL INSPECTION OF TREES 131 / 148 Each measurement is related to stochastic and systematic errors, an assessment of tree height and diameter too: S = H + D => S = (~±10%) + (~±5%) = ±15% ±15% is the mean error and does not necessarily cover the real value. Mostly, if you regard one measurement, the real value is covered within the interval of the doubled mean percentage error => S ±30%

132 2008 TECHNICAL INSPECTION OF TREES 132 / 148 Concepts of error description

133 2008 TECHNICAL INSPECTION OF TREES 133 / 148 Mean precent error (MPE) describes mean percentage deviation of the actual value from the mean value. The corresponding error beams do not necessarily cover the mean for all individual values. => x ±MPE may not contain mean

134 2008 TECHNICAL INSPECTION OF TREES 134 / 148 x ±2*MPE mostly covers real value => if you make one measurement and you do not know about the expected error, take x ±2*MPE as an easy and correct span! Example for height/diameter h=25m, d=50cm => h/d = 50 ±30% = 50 ±

135 2008 TECHNICAL INSPECTION OF TREES 135 / 148 Stress wave tomography of the same cross section: different machines => different results

136 2008 TECHNICAL INSPECTION OF TREES 136 / 148 Drill resistance profiles from the same sample: different device versions, different profiles (Mattheck&Bethge 1997)

137 2008 TECHNICAL INSPECTION OF TREES 137 / 148 Density profiles from x-ray and high-frequency measurements

138 2008 TECHNICAL INSPECTION OF TREES 138 / 148 Moment of inertia of cross section: critical influence of shape measurement!

139 2008 TECHNICAL INSPECTION OF TREES 139 / 148 Pulling tests and safety calculations Wind force Simple F = 0.5 * A * Cw * v² * ñ a bit more precise... v(x,y) wind speed ñ(x,y,t,p) air density (x,y) cw tu, gf canopy porosity drag coefficient turbulence, stand and roughness factors Wind load at the stem base: Windforce * length of lever arm = 0.5 * A * Cw * v² * ñ * L

140 2008 TECHNICAL INSPECTION OF TREES 140 / 148 Precision of tree safety calculation by pulling tests? Variance of bending moment B at stem base B = A + Cw + 2* v + ñ + L B (±20%) + (±30%) + (±2*30%) + (±5%) + (±10%) => B >> ±100%

141 2008 TECHNICAL INSPECTION OF TREES 141 / 148 Tree strength? Pulling tests determine MOE (modulus of elasticity) by measuring stress and elongation, but we need MOR (modulus of rupture) to assess tree safety. MOR of wood can only be measured directly by bending until failure! Thus many people are looking for non-destructive methods for MOE => MOR correlation. The best wood grading machines achieve r²~0.6 for correlation from MOE to MOR for small size timber without knots and decay. Non-laminar fibres, knots and decay bring r² down to 0.1 or even less (Wilcox 1978). => More than 90% of the variance of MOR can not be explained by MOE measurements in real trees with decay and irregular inside and outside shape. => MOE by pulling tests do not allow to evaluate MOR of stems.

142 2008 TECHNICAL INSPECTION OF TREES 142 / 148 (Sander 2005)

143 2008 TECHNICAL INSPECTION OF TREES 143 / 148 (Niemz 1993)

144 2008 TECHNICAL INSPECTION OF TREES 144 / 148 Assuming the simple equation: Tree safety = Tree strength / Wind load => Tree safety = Tree strength + Wind load => Calculated static tree safety ±200% For static wind load without taking into account dynamic behaviour and torsion effects! => Estimation error for real dynamic safety will even be much higher! Every expert claiming more precise values for tree safety has to clearly prove how he achieves this - independent from methods and persuasions!

145 2008 TECHNICAL INSPECTION OF TREES 145 / 148 I think, tree experts should be honest and clearly point out in reports that the evaluation may be based and/or guided by precise measurements or calculations but at the end can not be precise at all and is influenced by individual subjective decisions - yet still much better than doing nothing and evaluating without objective results!! Conclusions: " relative assessments of similar trees on similar stands under similar conditions work " absolute determination of wind load, stem strength and safety is nearly impossible.

146 2008 TECHNICAL INSPECTION OF TREES 146 / 148 Application examples: expert reports on trees

147 2008 TECHNICAL INSPECTION OF TREES 147 / 148 Final conclusions! A well trained visual tree inspection " is the most important base for proper risk evaluation.! Technical equipment helps in many cases, " but deep knowledge is required about trees, wood and techniques - before selecting the appropriate method and device - for application at the tree - for interpretation of the results - and for evaluation of the potential risk.! As Shigo already said: read, read, read, get educated and trained, and hurry up, because who comes to late...

148 2008 TECHNICAL INSPECTION OF TREES 148 / 148! will face a problem catching the arboricultural train in time... Thank you for your attention!