Guide to ISA Certified Arborists & ANSI Tree Care Standards
Key Takeaways:
- The two main ANSI tree care standards are ANSI A300 (how tree work should be performed) and ANSI Z133 (how it should be performed safely).
- An ISA Certified Arborist has met experience and exam requirements and follows a professional code of ethics, with additional arborist levels available for specialized and advanced work.
- Hiring a certified arborist who follows ANSI standards protects your trees, your property, and your investment, especially in Colorado’s demanding climate.
When you hire someone to prune, treat, or remove a tree, the difference between a true professional and a “guy with a chainsaw” comes down to training, credentials, and the standards they follow. This guide explains the two main ANSI tree care standards, the levels of arborist certification, and why choosing an ISA Certified Arborist matters for the long-term health of your trees.
What Are the ANSI Tree Care Standards?
ANSI tree care standards are the nationally recognized benchmarks for how professional tree work should be done. They’re developed through industry consensus and accredited by the American National Standards Institute (ANSI). Two standards form the foundation of professional arboriculture:
- ANSI A300 – The American National Standard for Tree Care Operations governs the quality and outcome of tree work. The ANSI A300 standards for tree care operations cover pruning, soil management, cabling and bracing, lightning protection, tree protection during construction, planting and transplanting, root management, integrated pest management, and tree risk assessment. They represent the industry’s standard of care and have even been treated as authoritative in U.S. courts.
- ANSI Z133 – This is the companion safety standard, covering the safety requirements for pruning, repairing, maintaining, and removing trees, plus equipment use and working near power lines. ANSI Z133 governs how the work is done safely, while A300 governs how well it’s done.
When a company says it follows ANSI A300 and ANSI Z133, it’s telling you the work will meet a recognized quality and safety bar rather than someone’s personal habits.
What Are the ANSI A300 Pruning Standards?
The ANSI A300 pruning standards (sometimes searched as the ANSI 300 tree trimming standards) define how branches should be removed to protect a tree’s long-term health and structure. They discourage outdated, damaging practices like topping and “lion-tailing,” and instead call for clearly defined objectives and proper cuts. Following these standards is the difference between trimming that strengthens a tree and cutting that slowly kills it.
What Is an ISA Certified Arborist?
An ISA Certified Arborist is a tree care professional credentialed by the International Society of Arboriculture (ISA) after demonstrating broad knowledge across tree biology, diagnosis, maintenance, and safety.
If you’re wondering what you need to be an arborist at this level, ISA certification requires one of the following, plus a passing score on a comprehensive written exam:
- Three or more years of full-time, practical experience in arboriculture, or
- A two-year degree in a related field (arboriculture, horticulture, forestry, or landscape architecture) plus two years of experience, or
- A four-year degree in a related field plus one year of experience.
Certified Arborists must also follow a professional Code of Ethics and earn continuing education units to stay current. The credential is voluntary, which is exactly why it signals real commitment.
Arborist Levels and Credentials
“Arborist” on its own is a general term. Anyone who works on trees can use it, with no guaranteed level of competency. The recognized arborist levels and credentials help you tell professionals apart:
- Arborist (Practicing) – A general term for anyone who cares for trees; no specific qualification is implied.
- ISA Certified Arborist – Has met the experience and exam requirements above and follows the ISA Code of Ethics.
- ISA Specialty Certifications – Certified Arborists who add focused credentials such as Utility Specialist, Municipal Specialist (Urban Forest Professional), Tree Worker Climber Specialist, or Tree Worker Aerial Lift Specialist.
- ISA Tree Risk Assessment Qualification (TRAQ) – A qualification for arborists who formally assess whether a tree poses a hazard.
- ISA Board Certified Master Arborist (BCMA) – The highest level of ISA certification; fewer than two percent of Certified Arborists hold it.
- Registered Consulting Arborist (RCA) – Awarded through the American Society of Consulting Arborists (ASCA) for expert consulting, appraisals, and reports.
Do Arborists Need to Be Licensed?
This is a common point of confusion, because certification and licensing are not the same thing. ISA certification is a voluntary professional credential, not a government license. Whether an arborist is legally required to be licensed depends on your state and city. Some municipalities require tree workers to be registered or licensed to operate, and any company applying pesticides or herbicides must hold the appropriate state license.
In Colorado, that means a reputable tree service should be licensed by the Colorado Department of Agriculture for spraying and disease treatment, and fully insured. Affordable Tree & Shrub Experts is both, and our work is overseen by ISA Certified Arborists who follow ANSI standards on every job.
Do I Need an Arborist? The Benefits of Hiring a Certified Pro
If a tree is large, near a structure or power line, diseased, or storm-damaged, the answer is almost always yes. Beyond safety, working with a tree service with a certified arborist gives you:
- Correct diagnosis – Certified arborists identify the real problem, whether it’s a pest, disease, or structural defect, before any cuts are made.
- Proper technique – Work that follows ANSI A300 protects tree health instead of causing slow decline through improper pruning.
- Safety and liability protection – ANSI Z133 compliance, licensing, and insurance protect you, your property, and the crew.
- Long-term value – Healthy, well-structured trees resist storm damage, live longer, and add to your property value.
- Peace of mind – A written assessment and clear recommendations, not guesswork.
In a climate as demanding as Colorado’s, with high winds, heavy snow loads, drought, and wildfire risk, that expertise pays for itself.
Work With Colorado's ISA Certified Arborists
At Affordable Tree & Shrub Experts, every service is designed and overseen by ISA Certified Arborists who follow ANSI A300 and ANSI Z133 standards, with over 40 years caring for trees across the greater Colorado Springs area. We’re licensed by the Colorado Department of Agriculture, fully insured, and BBB A+ rated, and every estimate is free.
Explore our full range of tree services, from trimming and removal to disease treatment and fire mitigation. Ready to get started? Contact us today to schedule a consultation or request a free estimate.
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