The wind can do immense damage to trees (and other shrubs and plants). But, by and large, trees have an impressive resilience to the intense forces that nature puts on them.
Wind blow (or throw) and wind snap are the two main catastrophic types of damage that might happen to trees in severe winds.
Trees are more likely to snap if the wind is in a different direction than is usual. That’s because as a tree grows, if it is frequently exposed to wind from one particular direction, the tree’s trunk will develop elliptically to withstand the wind. This gives the tree more strength in one direction than the others. If a storm brings wind from a different direction, the trunk of the tree will be subjected to pressures that it isn’t used to, that it hasn’t developed extra strength to resist and consequently that are more likely to snap it. This is known as wind snap.
Conversely, if the storm brings winds from the usual direction, the trunk of the tree is more likely to be able to withstand the wind, meaning it is less likely to snap. However, that means there is more probability of the whole tree blowing over and taking its root plate with it: known as wind blow.
Of course, lots of other factors come into play too. For example:
- If there has been a lot of rain and the soil is saturated it will be more slippy and that too favours the tree being uprooted rather than snapped.
- Anything that damages or disturbs tree roots, like excavations or construction activity, will make trees more vulnerable to the wind.
- So too will the removal of neighbouring trees or any other physical structures that had been providing shelter.
- Any tree that is compromised by damage, disease or rot has an increased likelihood of breaking in high winds.
- A tree that is in leaf will act like a sail catching the wind and therefore the forces on it will be intensified: deciduous trees sometimes suffer major damage as a consequence of relatively weak winds when they are in leaf, whereas the same wind speeds in winter would have left them largely undamaged.
Strangely enough, the dry summer we experienced this year in the UK may have helped to reduce the number of trees that were uprooted during the recent storm as the trees have had to root more deeply to keep their water supply going through the summer. Had it been a wet summer the roots would have been more shallow, the soils more slippy and more trees may have come down.