Resistograph® Testing in Tulsa, Oklahoma

When Resistograph® Testing May Be Appropriate

Resistance drilling may be useful when:

• A cavity is visible in the trunk or root flare
• Fungal fruiting structures suggest internal decay
• A historic wound may contain hidden decay
• A crack or split requires closer investigation
• Sounding suggests altered or hollow wood
• A trunk, branch, or buttress root has been damaged
• A lightning strike may have affected internal wood
• Vehicle or equipment impact has injured the tree
• A tree has survived fire or substantial heat exposure
• A previous branch or trunk failure has exposed decay
• Sonic tomography identifies an area requiring targeted confirmation
• A mature tree has been recommended for removal because of suspected internal decay
• Internal condition is relevant to an insurance or legal matter
• A high-value tree requires additional evidence before an irreversible decision
• Changes in internal condition need to be monitored over time
• A basic tree risk assessment identifies an uncertainty likely to affect the recommendation

Advanced testing should address a defined question.

It should not be performed automatically merely because a tree is old, large, valuable, leaning, or visibly defective.

How Resistograph® Testing Is Performed

1. Initial Tree and Site Evaluation

Before testing, the arborist evaluates:

• The client’s question
• Tree species
• Tree size and form
• Visible defects
• Wound history
• Cavities
• Cracks
• Fungal fruiting structures
• Crown architecture
• Root and soil conditions
• Previous failures
• Targets
• Site exposure
• Relevant findings from previous inspections or diagnostics

Test locations are selected to address the concern rather than drilling arbitrary points around the tree.

2. Select the Test Point and Direction

The arborist selects the entry point, drilling direction, and anticipated depth based on:

• Location of the suspected defect
• Trunk or branch geometry
• Load direction
• Cavity position
• Wound location
• Sonic tomography findings
• Accessible wood
• Nearby targets
• The specific question being investigated

More than one test may be required when the suspected defect cannot be adequately characterized by a single drilling path.

3. Prepare the Test Location

Loose bark, soil, mulch, or surface material may be moved as needed to establish an appropriate entry point.

The instrument is positioned and aligned along the selected drilling path.

4. Perform the Resistance Drill

The thin drilling needle advances through the tree at a controlled rate.

The instrument records relative resistance throughout the path and creates a digital or printed profile.

The drilling path may pass through:

• Bark
• Cambial region
• Sapwood
• Heartwood or central wood
• Decayed wood
• Cavities
• Cracks
• Other altered tissues

5. Review the Profile

The resulting graph is evaluated for:

• Expected wood-resistance patterns
• Abrupt reductions in resistance
• Extended low-resistance areas
• Complete resistance loss
• Changes associated with possible decay
• Potential cavity boundaries
• Measurement consistency
• Possible artifacts
• Relationship to visible defects

6. Interpret the Findings

The profile is interpreted in relation to:

• Species characteristics
• Tree geometry
• Wound history
• External symptoms
• Crown loading
• Root and soil conditions
• Testing depth and direction
• Other drilling paths
• Sonic tomography findings
• Site exposure
• Targets
• Assignment limitations

7. Develop Recommendations

Depending on the assignment, recommendations may include:

• Monitoring
• Repeat resistance drilling
• Sonic tomography
• Additional test points
• Prescription pruning
• Crown reduction
• Supplemental support evaluation
• Target management
• Root investigation
• Formal tree risk assessment
• Removal
• No immediate intervention beyond reassessment

Resistance-drilling data informs the recommendation but does not make the decision by itself.

Is Resistograph® Testing Invasive?

Resistograph® testing is considered minimally invasive because it creates a small-diameter drilling path through the wood.

It should not be described as non-invasive or as causing no injury.

The test creates a wound, although the diameter is substantially smaller than that produced by an increment borer or conventional drill.

Potential considerations include:

• Wounding of living tissues
• Exposure of internal wood
• The number of drilling paths
• Entry-point placement
• Tree species
• Tree vitality
• Existing decay
• Testing near important load-bearing areas
• Repeated testing over time

For these reasons, drilling should be:

• Based on a defined diagnostic need
• Limited to the number of tests reasonably necessary
• Directed toward the relevant concern
• Performed and interpreted by a qualified professional
• Avoided when the expected information is unlikely to affect the decision

The value of the information should justify the limited injury created by the test.

Does the Drilling Hole Need to Be Filled?

Resistograph® entry points are generally left open rather than filled with wound dressing, sealant, plugs, or other materials unless a specific product label, research-supported procedure, or unusual assignment condition supports a different approach.

Tree wound response depends on:

• Species
• Tree vitality
• Wound location
• Existing decay
• Environmental conditions
• Natural compartmentalization processes

No treatment can guarantee that the drilling path will remain free from discoloration, infection, or decay.

The purpose of minimizing needle diameter and test quantity is to reduce unnecessary injury while obtaining useful diagnostic information.

Resistograph® Testing and Sonic Tomography

Resistograph® testing and Arbotom® Sonic Tomography are complementary methods.

Arbotom® Sonic Tomography

Sonic tomography:

• Evaluates relative stress-wave patterns across an entire selected cross-section
• Produces a color-coded tomogram
• Helps identify broader patterns of altered wood condition
• Is generally nondestructive or minimally intrusive
• May identify locations where targeted confirmation would be useful

Resistograph® Resistance Drilling

Resistance drilling:

• Evaluates one narrow path through the wood
• Produces a high-resolution drilling-resistance profile
• Is minimally invasive
• May help evaluate the approximate depth and extent of altered wood along the selected path
• Can provide targeted confirmation of areas identified by tomography

A common advanced-assessment sequence may involve:

1. Conducting sonic tomography across a selected cross-section
2. Reviewing the tomogram for areas of altered stress-wave transmission
3. Selecting targeted resistance-drilling locations
4. Comparing the drilling profiles with the tomogram and visible tree conditions
5. Interpreting the combined findings within the broader tree risk or preservation assessment

The methods strengthen one another when used for an appropriate question.

They do not eliminate uncertainty or provide a mathematical guarantee of structural adequacy.

Resistograph® Testing, Arbotom®, and ArboRadix®

Davis Family Arbor Services may use three related but distinct advanced diagnostic approaches:

Arbotom® Sonic Tomography

Used to evaluate relative stress-wave patterns across selected trunk or branch cross-sections.

Resistograph® Resistance Drilling

Used to measure drilling resistance along selected pathways through wood.

ArboRadix® Root Detection

Used in conjunction with the Arbotom® sensor platform to investigate probable locations of significant roots within selected areas around a tree.

ArboRadix® cannot be used as a stand-alone system separate from the Arbotom® sensors.

Depending on the assignment, these methods may be combined to evaluate:

• Internal trunk condition
• Selected branch attachments
• Root location
• Potential construction conflicts
• Root-zone impacts
• Tree preservation options
• Tree risk concerns
• Forensic evidence

Each method answers a different question.

ArboRadix® identifies probable root locations but does not independently evaluate the internal wood density of those roots. Resistograph® testing may be used on exposed, accessible woody roots only when the expected information justifies the injury and the testing can be performed appropriately.

Resistograph® Testing and Tree Risk Assessment

Resistance drilling may be used as part of a Level 3 advanced tree risk assessment when a basic assessment identifies an important uncertainty involving internal wood condition.

It may help answer questions such as:

• Is the suspected cavity present along the selected path?
• Where does measurable resistance decrease?
• How much higher-resistance wood remains along the drilling direction?
• Does a tomogram’s suspected low-velocity area correspond with reduced drilling resistance?
• Does the tested area contain a crack or complete discontinuity?
• Would additional tests likely affect the management decision?
• Is continued monitoring reasonable?
• Is removal supported by multiple lines of evidence?

A formal tree risk assessment additionally evaluates:

• Specific failure scenarios
• Likelihood of failure
• Likelihood of impact
• Consequences
• Overall risk rating
• Mitigation options
• Residual risk
• Reassessment recommendations

Resistance drilling provides diagnostic data. It does not independently establish a risk rating.

Resistograph® Testing for Tree Preservation

Resistance drilling may provide valuable information when a mature or important tree has been recommended for removal because of suspected internal decay.

Decay does not automatically require removal.

A tree may contain:

• Historic wounds
• Localized cavities
• Internal decay
• Compartmentalized defects
• Response growth
• Altered but functional wood
• Structural adaptations developed over time

The management decision should consider:

• Location of the altered wood
• Remaining wood distribution
• Tree geometry
• Crown loading
• Root condition
• Species characteristics
• Response growth
• Targets
• Site exposure
• Available mitigation
• Client objectives
• Residual risk

Depending on the findings, preservation options may include:

• Monitoring
• Repeat testing
• Prescription pruning
• Crown reduction
• Supplemental support
• Target management
• Access restrictions
• Root-zone management
• Other site modifications

In other cases, the testing may provide evidence supporting removal.

Both outcomes are useful when the goal is an informed, evidence-based decision.

Resistograph® Testing at the Root Flare and Buttress Roots

Some structural concerns occur near the base of the tree.

Resistance drilling may be considered when evaluating:

• Buttress-root decay
• Basal cavities
• Root-flare wounds
• Fungal fruiting structures near the base
• Suspected root-collar decay
• Vehicle or equipment damage
• Construction-related root injury
• Fire or heat damage
• Areas identified through root-collar excavation

Testing near the base should be interpreted carefully because:

• Trunk and root geometry may be irregular
• Buttress roots change direction and thickness
• Soil and moisture conditions may affect the test
• Root systems are three-dimensional
• One drilling path cannot characterize the entire root plate
• Visible or measured decay does not independently establish anchorage capacity

Root Collar Excavation (RCX), AirSpade investigation, ArboRadix® root detection, sonic tomography, or other methods may be needed to provide additional context.

Resistance drilling does not directly determine whole-tree stability.

Resistograph® Testing in Major Branches

Resistance drilling may sometimes be used to investigate an accessible major branch or first-order branch when:

• A cavity is present
• A historic wound may contain decay
• A branch attachment has failed previously
• Fungal activity is suspected
• A crack requires additional evaluation
• The branch is an important component of a formal risk assessment

Testing aloft may require:

• Rope-based climbing
• Aerial-lift access
• Fall protection
• Specialized positioning
• Additional setup time
• Consideration of electrical and work-zone hazards

Testing a major branch should address a defined question and should be performed only when the information is reasonably likely to affect the management recommendation.

Monitoring Changes Over Time

Repeat resistance drilling may be useful when:

• A tree is retained with known internal decay
• A mature or historically significant tree is under long-term management
• Previous testing established a baseline
• A decay organism is present
• A wound or cavity is being monitored
• Mitigation has been performed
• The tree’s exposure or loading has changed
• Construction has occurred nearby

For meaningful comparison, follow-up testing should attempt to reproduce:

• Test-point location
• Drilling direction
• Drilling angle
• Equipment settings
• Depth
• Feed rate
• Documentation method

However, repeat drilling should not automatically follow the exact previous pathway because additional wounding may be created and precise replication may not be possible.

Natural growth, moisture, wound response, equipment variation, and slight changes in drilling path can affect profile comparisons.

Resistance-drilling graphs should not be interpreted as measuring an exact annual rate of decay progression.

Resistograph® Testing for Tree Forensic Investigations

Resistance drilling may support forensic assignments involving:

• Tree or branch failure
• Construction damage
• Vehicle impacts
• Lightning damage
• Fire exposure
• Root injury
• Historic pruning wounds
• Questions about internal decay
• Disputed removal recommendations
• Insurance matters
• Litigation
• Municipal or public-property claims

Testing may document internal resistance patterns in portions of a tree that remain available for examination.

It generally cannot reconstruct the precise internal condition of material that has already been:

• Removed
• Chipped
• Burned
• Ground
• Discarded
• Substantially altered after failure

Forensic interpretation may also require:

• Examination of failure surfaces
• Photography
• Tree and stump measurements
• Weather records
• Maintenance records
• Construction documents
• Witness information
• Sonic tomography
• Root investigation
• Laboratory analysis
• Other available evidence

Resistance drilling is one line of evidence within the larger investigation.

Municipal and Public-Agency Resistograph® Testing

Davis Family Arbor Services provides Resistograph® testing and related consulting for:

• Municipalities
• Public agencies
• Parks
• Campuses
• Schools
• Historic properties
• Public facilities
• Streetscapes
• Commercial properties
• HOAs
• Institutions
• Development projects

Potential applications include:

• Evaluating mature public trees
• Investigating cavities and fungal activity
• Supporting preservation decisions
• Supporting formal tree risk assessments
• Establishing monitoring baselines
• Evaluating trees near occupied public areas
• Documenting conditions before or after construction
• Supporting municipal planning and budgeting
• Providing additional evidence for board or public review

The testing scope and report format are developed according to the tree population, management question, project deadlines, procurement requirements, and intended use.

What the Written Report May Include

Depending on the agreed scope, a Resistograph® report may include:

• Client and property information
• Assignment purpose
• Inspection and testing date
• Tree identification
• Species
• Trunk diameter
• Approximate height and crown spread
• Tree location
• Test-point locations
• Test-point height
• Drilling direction and angle
• Drilling depth
• Site and target information
• Visible defects and symptoms
• Wound and management history
• Photographs
• Drilling-resistance profiles
• Interpretation of measured patterns
• Comparison with sonic tomography when included
• ArboRadix® findings when relevant
• Structural considerations
• Tree risk information when separately scoped
• Management recommendations
• Reassessment recommendations
• Assignment assumptions and limitations
• Arborist credentials and signature

Not every assignment requires every listed item.

The written proposal identifies the trees, test locations, anticipated number of drilling paths, related diagnostics, report format, fees, and schedule before testing begins.

Limitations of Resistograph® Testing

Resistance drilling has important limitations.

It Evaluates Only a Narrow Path

Each test provides information along a single drilling pathway.

Decay, cavities, cracks, or sound wood may be present nearby without intersecting the needle path.

Wood Resistance Is Not the Same as Structural Strength

The instrument measures drilling resistance rather than:

• Bending strength
• Shear strength
• Root anchorage
• Whole-tree stability
• Likelihood of failure
• Likelihood of impact
• Consequences

Species and Wood Anatomy Matter

Natural variations in wood density, growth rings, resin, moisture, and anatomy may influence the profile.

Geometry Matters

Irregular trunks, buttress roots, included bark, cavities, seams, cracks, and unusual growth may affect interpretation.

Test Selection Matters

A poorly selected test location may miss the condition of concern or produce information unrelated to the management question.

Testing Creates a Wound

Although minimally invasive, resistance drilling creates a narrow pathway through living and nonliving tissues.

The number and placement of tests should therefore be limited to those reasonably justified by the assignment.

No Single Threshold Applies to Every Tree

There is no universal drilling-resistance percentage, residual-wall measurement, or cavity dimension that automatically determines whether every tree should be retained or removed.

Tree management requires interpretation of the complete tree and site.

Professional Qualifications

Resistograph® testing and related consulting services are led by Brad Davis, whose qualifications include:

• ISA Board Certified Master Arborist® MW-6328B
• ISA Tree Risk Assessment Qualified
• ISA Florida Chapter Prescription Pruning Qualified
• Member, International Society of Arboriculture
• Member, American Society of Consulting Arborists

Findings are interpreted using:

• Tree biology
• Species characteristics
• Wood anatomy
• Tree architecture
• Visible defects
• Site conditions
• ISA tree risk assessment methodology
• Applicable ANSI A300 Tree Care Standards
• ISA Best Management Practices
• Current arboricultural research
• Sonic tomography findings when included
• Other available diagnostic information

The equipment records drilling resistance. Professional interpretation connects those measurements to the tree, site, and management question.

Fees, Scheduling, and Deliverables

Resistograph® testing is a specialized professional consulting service.

Fees depend on:

• Number of trees
• Number of test points
• Tree size and geometry
• Testing height
• Aerial-access requirements
• Site access
• Tree condition
• Sonic tomography requirements
• Root-flare or AirSpade investigation
• ArboRadix® root-detection work
• Mapping
• Reporting requirements
• Intended report use
• Travel
• Project deadlines

A written proposal may specify:

• Included trees
• Anticipated test locations
• Number of drilling paths
• Testing depth
• Optional sonic tomography
• Optional ArboRadix® root detection
• Optional AirSpade investigation or RCX
• Report format
• Fees
• Payment terms
• Anticipated delivery schedule
• Assignment limitations
• Optional follow-up services

Report delivery timing depends on project scope, number of tests, data review, related diagnostics, documentation requirements, and current workload.

Expedited service may be available for agreed construction, municipal, insurance, legal, or real estate deadlines.

Service Area

Davis Family Arbor Services provides Resistograph® testing and related consulting throughout:

• Tulsa
• South Tulsa
• Broken Arrow
• Jenks
• Bixby
• Sapulpa
• Glenpool
• Sand Springs
• Tulsa County
• Wagoner County
• Surrounding northeastern Oklahoma communities

Statewide assignments may be considered for:

• Municipalities
• Public agencies
• Attorneys
• Insurance professionals
• Developers
• Commercial properties
• Historic properties
• Institutions
• Technically complex or high-value trees