Arborist & tree permit glossary

Jump to a term

• Certified arborist supervision letter
• Consequences of failure
• Critical root zone (CRZ)
• DBH (diameter at breast height)
• Dead-load pruning
• Drip line
• Hazard tree
• Heritage tree
• ISA Certified Arborist
• ISA risk matrix
• In-lieu mitigation / Tree Trust Fund
• Likelihood of failure
• Mangrove preemption
• Maximum fine per tree
• Mitigation planting
• Municipal code reference
• Native-plant preemption
• Permit applicant
• Permit fee
• Protected species list
• Protected tree
• Replacement ratio
• Required report sections
• Retention value
• Specimen tree
• Structural pruning
• TRAQ (Tree Risk Assessment Qualification)
• TRAQ Level 1 assessment
• TRAQ Level 2 assessment
• TRAQ Level 3 assessment
• Target zone
• Typical processing time

TRAQ

9 terms

TRAQ (Tree Risk Assessment Qualification) #

Tree Risk Assessment Qualification is the International Society of Arboriculture's credential and methodology for documenting tree risk. TRAQ defines a structured workflow — site context, target identification, likelihood of failure, likelihood of impact, consequences, and a risk matrix — that produces a defensible rating a permitting office, insurer, or court can audit. Holding the qualification means an arborist has passed the ISA TRAQ course and exam and renews the credential on a five-year cycle.

TRAQ Level 1 assessment #

A limited visual assessment, usually drive-by or walk-by, used to screen large tree populations for obvious defects. Level 1 is appropriate for utility right-of-way patrols, post-storm sweeps, and HOA-wide inventories where the goal is triage, not per-tree documentation. It does not produce a TRAQ risk rating on its own; trees flagged in a Level 1 sweep are typically referred to a Level 2 follow-up.

TRAQ Level 2 assessment #

The basic 360-degree visual inspection of an individual tree from the ground. Level 2 is the standard arborist report used for permit applications, real-estate transactions, and most consulting work. It documents species, dimensions, condition of roots, trunk, and crown, identifies likely failure modes and targets, and produces a documented risk rating using the ISA risk matrix. Most municipal permit packets expect a Level 2 report by default.

TRAQ Level 3 assessment #

An advanced assessment that goes beyond ground-based visual inspection — sonic tomography, resistograph drilling, root collar excavation, aerial inspection by climbing or lift, or load testing. Level 3 is invoked when a Level 2 finds a defect that needs deeper investigation before a recommendation can be defended. It is more expensive and slower, and is typically scoped as a follow-on engagement rather than a default report type.

ISA risk matrix #

The 4×3 matrix that combines likelihood of failure-and-impact (improbable, possible, probable, imminent) with consequences of failure (negligible, minor, significant, severe) to produce a final risk rating of Low, Moderate, High, or Extreme. The matrix is the part of a TRAQ report that municipal reviewers, attorneys, and adjusters look at first. Skipping it or substituting a custom rating system is the most common reason a report is sent back.

Likelihood of failure #

An estimate of the probability that a specific defect or load condition causes a part of the tree (or the whole tree) to fail within a defined time horizon — usually three years. Categories are improbable, possible, probable, and imminent. The estimate is informed by visible defects, species failure profile, exposure, and recent loading history, not just the size of the defect.

Consequences of failure #

An estimate of how severe the outcome would be if the failure described in likelihood-of-failure occurred and struck the identified target. Categories are negligible, minor, significant, and severe. Consequences depend on what the target is (a parked car versus an occupied building) and how often it is occupied, not on the tree itself.

Target zone #

The area within reach of a tree's potential failure where people, vehicles, or structures could be struck. Target zones are characterized by occupancy rate (constant, frequent, occasional, rare) so that consequences-of-failure can be estimated honestly. A 60-foot oak over an unoccupied gravel lot is not the same risk as the same oak over a school crosswalk; the target zone is the difference.

Hazard tree #

Informal term, increasingly avoided in modern arboriculture, for a tree with a defect likely to cause failure that has a target within striking distance. Modern TRAQ documentation prefers the explicit risk rating (Low/Moderate/High/Extreme) over the binary hazard label, because the rating communicates how the tree compares to other trees and what mitigation is proportionate. Some municipal codes still use 'hazard tree' as a defined permit category.

Tree biology

4 terms

DBH (diameter at breast height) #

Diameter of the tree trunk measured 4.5 feet above grade on the uphill side. DBH is the most common dimension cited in tree ordinances because it is repeatable and does not require climbing. Many cities define a protected tree as any tree above a DBH threshold (commonly 6, 8, 12, or 24 inches). Multi-stem trees are usually measured by either the largest stem or a square-root-of-sum-of-squares calculation, depending on the jurisdiction.

Drip line #

The vertical projection on the ground of the outer edge of a tree's canopy. The drip line is used as a rough proxy for the protected root zone in tree-protection ordinances and grading-permit conditions. It is conservative — actual structural roots typically extend well beyond the drip line — but it is easy to mark with paint or fencing during construction, which is why so many codes anchor protections to it.

Critical root zone (CRZ) #

The area of soil around a tree where root disturbance is most likely to cause structural or biological harm. CRZ is most often calculated as a circle with radius equal to one foot per inch of DBH, centered on the trunk, though some agencies use 1.5x or the drip line plus a buffer. Construction inside the CRZ usually triggers tree-protection plans, supervision by a certified arborist, and post-construction monitoring.

Retention value #

A composite assessment of how desirable it is to retain a particular tree, weighing its species, condition, dimensions, structural integrity, ecological role, and replaceability. Retention value is sometimes a numeric score and sometimes a categorical (low/moderate/high/exceptional) judgment. It is distinct from risk: a high-retention-value tree can still be high-risk, in which case the recommendation is usually mitigation rather than removal.

Pruning & care

2 terms

Structural pruning #

Pruning aimed at developing a single dominant leader and well-spaced scaffold branches in young or maturing trees, reducing the long-term risk of co-dominant stem failure and weak attachments. Distinct from cleaning or thinning, structural pruning is a multi-cycle program over a tree's first 20–25 years and is one of the highest-return interventions a consulting arborist can recommend.

Dead-load pruning #

Removal of dead, dying, and broken branches to reduce the risk that they fall as discrete projectiles. Sometimes called deadwooding. Dead-load pruning is one of the most defensible mitigation recommendations on a TRAQ report because it reduces likelihood of failure for a specific identifiable hazard without altering the live tree's form.

Permits & ordinance

16 terms

Mitigation planting #

Replacement trees planted as a condition of approval for a removal permit. The number, size, and species of mitigation plantings are dictated by the local ordinance — typically expressed as a replacement ratio (e.g. 1:1, 2:1, or based on DBH inches) — and the planting plan is usually attached to the permit. Failure to install or maintain mitigation plantings is one of the most common post-permit code violations.

Protected tree #

Any tree that meets the local ordinance's threshold for permit protection — usually a combination of DBH minimum, species, and location (street tree, public-property tree, or tree in a riparian buffer). Removal of a protected tree without a permit is a code violation, often with per-tree fines that can run into five figures. The threshold varies widely between cities, which is what most ordinance pages on this site exist to document.

Specimen tree #

A tree given heightened protection by a local ordinance because of unusual size, species, age, or visual prominence. Specimen designation usually carries a higher replacement ratio, a stricter standard for approving removal, and sometimes a public hearing requirement. Some jurisdictions use 'specimen' as a synonym for heritage tree; others reserve it for an even more selective tier.

Heritage tree #

A tree designated by a city or county for elevated protection on the basis of size, species, age, historical association, or location. Heritage tree status typically requires city-council or planning-commission approval to remove, may carry replacement ratios of 3:1 or higher, and sometimes blocks removal entirely except for documented hazard. Some jurisdictions maintain a public registry; others apply the designation by definition (e.g. any oak above 36 inches DBH).

Replacement ratio #

The number of replacement trees a permit applicant must plant for each tree removed, expressed as a ratio (e.g. 1:1, 2:1, 3:1) or as inches-of-DBH (e.g. one inch of replacement tree caliper for every two inches of removed-tree DBH). Heritage and specimen trees usually trigger higher ratios. The ratio is the single number most often cited from a permit ordinance and is on the headline of every city page on this site.

In-lieu mitigation / Tree Trust Fund #

Cash payment a permit applicant can make in place of planting required replacement trees on site, used when the parcel cannot physically accommodate the mitigation planting. Funds typically flow into a municipal Tree Trust Fund, Tree Mitigation Fund, or Urban Forestry Fund, and are spent on planting in parks, street rights-of-way, or other public land. The per-tree fee is set by the ordinance and is usually higher than the cost of self-planting, to encourage on-site mitigation.

Permit applicant #

The party legally authorized to apply for a tree removal permit. Most ordinances require the applicant to be the property owner, an authorized agent in writing, a licensed contractor named on a building permit, or a city department for public-property trees. Tenant-applied permits are usually rejected without owner authorization. Applicant requirements are often the first thing to verify before scoping a permit-driven removal job.

Certified arborist supervision letter #

A signed letter from an ISA-certified arborist confirming that work performed under a permit (pruning, root-zone construction, removal) was conducted under their supervision and consistent with ANSI A300 standards. Many permits are conditioned on a supervision letter being filed before final inspection. The letter is short — usually one page — but its absence is one of the most common reasons a permit is held open and a certificate of occupancy is delayed.

Native-plant preemption #

A category of state-law preemption that limits a city's authority to require, restrict, or regulate native plants on private residential property — most prominently in Florida (statute 581.187), where municipalities cannot prohibit the trimming or removal of healthy mangroves on a homeowner's own property without specific findings. Preemption clauses can override a local tree ordinance for a specific species or habitat type, so the first question on a Florida coastal removal is whether mangrove preemption applies.

Mangrove preemption #

Florida-specific preemption under the Mangrove Trimming and Preservation Act (FS 403.9321–403.9333) that places trimming and alteration of mangroves under state — not local — jurisdiction. Property owners can perform certain trimming on their own riparian property without a permit; larger work requires a Professional Mangrove Trimmer or DEP authorization. Local tree ordinances cannot impose stricter requirements on mangroves except where the act explicitly allows.

Required report sections #

The specific content sections a municipal tree-removal permit packet expects an arborist report to contain — typically some combination of methodology, site context, tree inventory with dimensions and condition, defect documentation, risk rating, recommended action, mitigation plan, and arborist credentials with signature. Submitting a report that is missing one of these sections is the most common reason a permit application is returned for revision.

Municipal code reference #

The chapter, article, and section number of the local code that governs tree protection in a given jurisdiction (for example, San Francisco Public Works Code Article 16, or Atlanta City Code Chapter 158). Citing the municipal code reference verbatim on the permit application — not just paraphrasing the rule — is one of the small details that distinguishes a report from a competent consulting arborist from a report a reviewer will return for clarification.

Typical processing time #

The time, in business days or weeks, between submitting a complete tree-removal permit application and receiving a decision. Processing time varies widely between jurisdictions — same-day for routine residential permits in some cities, six-to-eight weeks for heritage-tree applications that require a public hearing. Quoting an honest processing time to clients up front is the single biggest driver of post-engagement satisfaction in consulting practice.

Permit fee #

The application fee charged by the local jurisdiction to review a tree-removal permit. Fees range from no charge for street-tree removals in some cities to several hundred dollars per tree for heritage or specimen-tree applications. Fee schedules are usually set by city resolution, updated annually, and are separate from any required mitigation payments or fines for unauthorized removal.

Maximum fine per tree #

The upper limit a city can assess as a civil penalty for unauthorized removal of a protected tree. Maximum per-tree fines range from a few hundred dollars to over $10,000 per tree, with multipliers for heritage trees and repeat offenders. Fines are typically separate from — and additive to — the requirement to plant replacement trees and pay an in-lieu fee. The high end of the fine schedule is what makes pre-removal arborist consultation cost-effective on contested sites.

Protected species list #

A jurisdiction-specific list of tree species afforded protection regardless of size — typically native oaks, redwoods, and culturally significant species. Removal of a listed species is regulated even if the tree is below the general DBH threshold, often with elevated replacement ratios and mandatory permit review by an urban-forestry officer. The list is one of the first things to check on any new site, because it changes the answer to 'is this tree protected.'

Credentials

1 term

ISA Certified Arborist #

A professional credential issued by the International Society of Arboriculture, attesting that the holder has passed a written exam covering tree biology, pruning, soil management, diagnosis, and safety, and accumulated at least three years of full-time arboricultural experience. Certification is renewed every three years through continuing education. Many permit ordinances explicitly require an ISA Certified Arborist to author or supervise tree work; some require the higher-tier ISA Board Certified Master Arborist for heritage or specimen-tree work.