Have you noticed any downed trees? I have, along with cracked and even broken branches in yards and on rooftops. Some, if not most, can be blamed on the massive amounts of rain we’ve had over the past couple of weeks.
Since we haven’t had a hurricane or tornado recently, we might attribute these fallen trees to the pattern of consistent rainfall. What is it that happens during these long periods of heavy rain that can cause trees to fall? Let’s look at a few pertinent areas.
First, the health of a tree is very important. Sickly trees are usually weaker, therefore more fragile during a windy, rainy period. They may have unnoticed insect or fungus infestations, which can weaken them structurally, causing broken branches. A sick tree may have a weakened root system, which can damage branches and may cause the tree to lean to one side, resulting in its base being more unstable.
Next, age might play a factoring role. Some species of trees have a fairly short lifespan. Trees that are toward the end of their life expectancy will be more likely to be damaged during a heavy storm than those that are younger. Newly planted trees also are susceptible because they haven’t developed a strong root system yet. This is why new trees may need staking early on.
Another feature of a tree that increases its chances of damage is its canopy. A heavy canopy, thick with leaves, catches more wind and can cause limb damage as well as cause the tree to blow over during a heavy wind — especially if the canopy is wet. Also, the shape of a tree’s canopy can cause it to catch more wind and increase the likelihood of uprooting under the right conditions. A tree with compact branches and most of its foliage at the top will catch more wind than a species with sparsely arranged branches. Also, when a tree’s canopy is in a U shape or a V shape, one or both of the forks could be weaker than a single-trunked tree. Fast-growing trees may also have an increased risk since their canopy may thicken before the root system is able to secure it.
While researching this topic, I learned the term “windthrow,” which describes a tree that has been uprooted. According to David R. Foster, director of the Harvard Forest at Harvard University, “The tree trunk acts as a lever, and so the force applied to the roots and trunk increases with height.” Because we had so much rain with some accompanied winds, I think a combination of the two was just enough to uproot some very substantial trees in this area.
Finally, soil plays a major role in the stability of a tree. Remember, in a mature tree, most of the root system is within the top 18 inches of the soil. Trees planted in fairly shallow, loose soil, can grow just fine for years. Then, as in the last few weeks, we get a long saturating rain and all of a sudden the tree uproots.