Many homeowners are concerned about wind damage to trees. While 20 miles per hour (mph) winds can cause smaller trees to sway and large branches to move, they typically do not fell healthy, established trees.
Understanding Wind Strength and Tree Resilience
Trees are resilient and designed to withstand various wind conditions. Winds around 20 mph cause small trees to sway but typically do not result in widespread damage. Trees adapt to wind by developing stronger wood and flexible branches, allowing them to bend without breaking. This flexibility and a robust root system enable most trees to resist typical wind forces.
Key Factors Influencing Tree Vulnerability
While healthy trees withstand moderate winds, several factors can compromise stability, making them vulnerable even to lower speeds. Tree health significantly influences wind resistance; decay, disease, or pest infestations weaken wood and structural integrity, increasing the risk of limb failure or uprooting.
Tree species characteristics also play a role in wind resistance. Some species, like willow, silver maple, and Bradford pear, have brittle wood or shallow root systems, making them more prone to damage. Conversely, trees like oaks and maples possess stronger wood and more extensive root systems, better equipping them to handle higher wind speeds.
Root system integrity is another factor. Damage from construction, compaction, or limited rooting space prevents a tree from establishing strong anchorage. Trees in urban environments, often with restricted root space, are particularly susceptible. Saturated soil conditions can drastically reduce a tree’s anchorage. Waterlogged soil loses its ability to grip roots, making even healthy trees prone to uprooting.
Previous damage or structural defects also increase vulnerability. Improper pruning or structural issues, like co-dominant stems with included bark, can create weak points that may fail under wind stress. The size and shape of a tree’s canopy influence how much wind it catches. An overly dense or asymmetrical canopy acts like a sail, increasing wind forces on the trunk and roots, making the tree more prone to windthrow.
When Do Trees Become a Real Hazard?
While 20 mph winds pose a low risk, concerns for tree stability begin at higher speeds. Sustained winds or gusts exceeding 39-40 mph can cause noticeable damage, such as breaking twigs and small branches. As wind speeds increase, so does the potential for more significant damage. Winds reaching 47-54 mph can cause light structural damage to buildings and result in branches breaking from trees.
The threshold for uprooting or breaking large trees often falls within the 55-63 mph range. During severe storms, winds reaching 60 mph or higher can lead to considerable damage, including snapped trunks or entire trees being pushed over. Winds above 70 mph can cause widespread destruction, even to healthy trees. It is prudent to have at-risk trees assessed by a professional arborist, especially if vulnerability factors are present.