Arboriculture is a field filled with diverse techniques and philosophies – especially when it comes to pruning. From aspect ratios to species-specific recovery times, you can find varying opinions among arborists worldwide. However, emerging research and field experience consistently point to one important truth: A holistic, biologically informed approach to pruning leads to healthier, longer-living trees.

When possible, pruning should focus on second- and third-order branches to keep wounds and decay away from the trunk. All sketches by C. Abuhl 2025.

Trees are more than landscape features
Too often, trees are treated like static decorations – shade providers or obstacles to be trimmed at will. But this perspective ignores a basic truth; trees are living organisms. They breathe, respond to trauma, adapt to their environments and, perhaps most critically, benefit human health in measurable ways.

Scientific studies confirm what many arborists have long suspected. The removal of urban canopy due to pests (like the emerald ash borer) has been linked to significant increases in cardiovascular and respiratory deaths in affected regions. In Oregon, neighborhoods with a 10% increase in tree canopy showed higher birth weights and improved health outcomes. Other studies suggest trees improve mental health, academic performance and even recovery rates in hospitals.

The arborist’s responsibility
Pruning is essential, but it must be done responsibly. As the late Dr. Alex Shigo, pioneer of modern arboriculture, once said, “Pruning is one of the best things we can do for a tree, but also one of the worst.”

Our role as arborists isn’t just to respond to requests; it’s also to educate, assess and act in the best interest of the tree. While it may be tempting to remove a branch simply because a client insists, we must ask: Does this benefit the tree, or are we just creating long-term damage for short-term satisfaction?

I’ve often seen clients move on when we have refused to over-prune or remove healthy limbs. But I’ve seen far more who developed trust, loyalty and appreciation once they understood the science behind our approach.

Pruning principles that preserve health
One common mistake is the removal of first-order branches, the large limbs directly connected to the trunk. Research shows that cuts made here, especially without a clear branch collar, lead to higher levels of internal decay. Even with collars, different species have varying abilities to compartmentalize damage.

When possible, pruning should focus on second- and third-order branches to keep wounds and decay away from the trunk. In some cases, a staged pruning – where a partial removal allows the collar to develop before the final cut – can help reduce long-term harm. Though this may temporarily reduce aesthetic appeal, it supports biological healing and longevity.

Rather than thinning, reduction cuts can dramatically lower torque and stress on a tree’s structure.

The problem with thinning
Despite modern evidence that it can be detrimental, canopy thinning is still common. Arborists may believe it allows wind to pass more easily, but in reality, it can destabilize the tree by removing internal branches that act as dampeners. Studies, including wind-tunnel experiments, clearly show that reduction pruning – shortening extended limbs – is far more effective at reducing wind stress.

By reducing the length of overextended limbs, arborists can dramatically lower torque and stress on a tree’s structure without compromising its form or function.

In many cases, crossing limbs create natural braces that strengthen junctions and improve resistance to wind or loading stress.

Rethinking crossing branches
Traditionally, rubbing or crossing branches have been seen as problems. But new research suggests otherwise. In many cases, crossing limbs create natural braces that strengthen junctions and improve resistance to wind or loading stress. Wood samples from these junctions have been shown to be denser and more structurally sound than surrounding tissue.

Of course, not all crossing limbs are helpful. But the assumption that they are inherently harmful is no longer supported by science. The key is evaluation, not automatic removal.

Understanding decay – it’s not always a problem
One of the most misunderstood areas of arboriculture is tree decay. Many assume decay equals danger, but that’s not always true. In fact, trees with internal decay can still be structurally sound, especially if they’re showing strong response growth around the affected area.

Not all decay types are equal. Basal rot, for example, can be severe, affecting root systems and leading to sudden failure. But superficial heartwood decay, especially in older trees, does not always indicate imminent risk. Arborists must use knowledge, not fear, to assess these situations.

A call for industry-wide integrity
As our urban forests age, arborists must lead the charge in education, stewardship and science-based care. It’s not enough to maintain trees, we must advocate for them also.

Imagine an industry with a unified “duty of care,” where pruning practices are consistent, evidence-based and focused on tree longevity. Where arborists are trusted advisors, not just hired hands. Where fewer trees fail due to poor decisions, and more live to thrive in the landscapes we share.

Many assume decay equals danger, but that’s not always true.

That future begins with how we prune.

Nicholas Abuhl, an ISA Certified Arborist and an ISA Tree Risk Assessment Qualification-credentialed arborist, has been in the industry for 16 years. He also is founder and owner of Osage Arbor Care, a tree care business he launched earlier this year in Troy, Missouri.