Storm Preparation for Trees: Essential Tips for High Wind and Hurricane Readiness

As hurricane season arrives - and as storm intensity increases generally - we might eye our favorite trees with trepidation. Sure, they’ve weathered storms in the past but doesn’t every tree have its day? Fueled by this kind of anxiety, tree care companies get lots of calls from homeowners trying to feel better about their trees.

Proactive tree care is often good tree care, but caution is warranted where storm preparation is concerned. A tree's hazard potential can be reduced through good care. Unfortunately, much of the work done in the name of safety runs counter to best practices and can actually increase a tree’s risk profile. Four examples of common practices that can increase a tree's risk profile include:

• Excessive thinning

• Crown raising or "limbing up"

• Lion’s-tailing

• Topping
  

Thinning a canopy to allow air to pass through feels reasonable:

Less wind drag = greater safety

But trees are great at self-optimizing. In response to gravity and wind loads, trees add wood where they need it most. Thinning a tree so much that wind sails through its canopy exposes branches to wind in directions and speeds they’ve never experienced before. Thinning isn't categorically bad. Sometimes thinning is good Arboriculture. But significantly changing the way a tree relates to wind loads can be a recipe for disaster.

“Limbing up” a tree by removing the lowest branches overhanging a roof can also be a mistake. As the fall distance between a branch and a target increases, so does the impact speed. A branch that breaks and free-falls 5’ before impacting will hit at roughly 17mph. The same branch falling from 10’ above the roof will impact at roughly 25mph. Furthermore, low branches can potentially protect a target from higher branches that break out.

Lion’s-tailing removes a tree’s interior leaving poufs of foliage at the end of each branch. Leaving only the outermost foliage retains canopy where the wind-load is greatest. Knowing that the more compact we are the less wind load we experience, our own physical response to high wind is to crouch. Lion’s-tailing does the opposite. It leaves a tree's head held high. This type of pruning also doesn’t leave enough foliage for the tree to sustain itself well.

photo credit: Las Aventuras

Topping cuts create a type of wound that trees struggle to respond to. They do make trees more compact, reducing wind load, but it’s more like a beheading than a crouch.

photo credit: Community Tree Preservation

Topping encourages vigorous and poorly attached suckering growth at a spot that's likely to decay, as seen in the cross section below of an old topping cut:

A topped tree might withstand its first hurricane better than it would have with no pruning at all, but the combination of explosive suckering growth and increasing decay are likely to make it more vulnerable to storm damage - and more dangerous - in the long run. Topping is such a destructive practice that it (along with lion’s-tailing) is cautioned against by the International Society of Arboriculture and banned in some jurisdictions.

So what can be done? 

Prune the outer (rather than inner) canopy to make a tree more compact overall. Doing so by making relatively small diameter cuts - around the size of your wrist - keeps wound-size small. This minimizes the chances of decay and doesn't trigger explosive suckering. 

Leave a tree’s inner canopy largely intact for maximum photosynthesis. This maintains wind-loading that trees have literally grown accustomed to and it leaves lots of future pruning options.

Inspect for vulnerabilities. Trees often fail in predictable ways. Parts that are likely to fail can frequently be identified in advance by a trained eye. Consider a tree risk assessment. If parts of the tree seem particularly vulnerable, an inspector may recommend measures such as load reduction through pruning or supplemental support systems like cables and braces.

Tree failure at an included union. Photo credit: Joseph OBrien, USDA Forest Service

Plant for stability. A lone tree tends to be easier to topple than a tree whose root system is intermingled with adjacent trees and shrubs. Safety in numbers! This doesn’t require lots of big trees. A series of smaller trees and shrubs around a large tree can create a more stable root network while also adding color, texture and scale.

Investigate soil conditions. The old adage is, "For healthy plants, grow your soil". Great soil conditions will keep your trees healthier and can make them more stable. Where soils have been compacted, roots may be particularly shallow and the whole root plate may be more prone to lifting.

Take heart!

Even after severe weather events the majority of trees are left standing. If you have a big old tree it has already proven its resilience through many storms. If you're concerned about your tree's readiness for the next big one, here's a checklist to safeguard your trees and calm the nerves:

• Inspect for overall health and structural defects - mitigate as needed

• Investigate soil conditions

• If any crown reduction is warranted, prune from the outside in and leave interior growth