Sounds like a simple enough question, right? However, it turns out we can’t give a very good answer.
For a big old tree in a city or a park, it is important for safety reasons to know how likely it is to snap in the wind. Therefore, qualified arborists tend these trees and perform regular health checks.
For a plantation forest, wind damage can cause millions of pounds of damage. Therefore, a lot of scientific effort has been put into measuring tree breaking points, and predicting wind damage.
For a natural forest, wind damage is one of the key drivers of the carbon cycle and limitation of carbon stocks, making it an important factor in predicting climate change. Therefore, I have been wandering around trying to measure a few trees with no training or expertise! Ok, that is a bit overdramatic, I am doing a PhD on the subject. But the point is that this is a massively understudied topic and could prove to be pretty significant.
I have been examining wind damage in natural forests by running an experiment in a temperate forest in the UK and in a tropical forest in Borneo. This involved attaching strain gauges to trees to measure how they bend in the wind (left hand image below). We also fixed some anemometers to tall trees to measure the wind speed (right hand image below). Once that data is collected we can plot wind speed against bending and predict how strong a wind gust would have to be to snap the tree. There are a load of problems about resolution, data quality, accuracy of the predictions and so on, but the big picture is nice and straightforward.
The only issue is the equipment. Unfortunately, this equipment is not widely used, and so is not commercially available. We picked up some bits and pieces, built the rest, hooked it up to an old data logging system and hoped it would work out. It didn’t! As I was often warned before I started – fieldwork can be a pain. We had error message after error message, unexplained equipment failures, nonsense data and logistical nightmares. In Wytham I was always on hand to go and fix something if it went wrong. In Borneo I had to leave it in the forest for five months unattended. The result was that, by the time I finished my fieldwork, I pretty much understood all the equipment and got it all working just nicely. If I could re-run the experiments with my current knowledge it would be so easy now!
So the data is in and analysis has begun. We are now able to predict the critical wind speed at which trees will break in Wytham and in Danum. The field data only cover a small number of trees in each site of course, but we are working on some models to generalise it. Hopefully, we will soon be able to predict the critical wind speed for thousands of trees, or even entire forests, and this will help us in our overall goal of better understanding the forest carbon cycle.
Oh, and we also got to visit the tallest tree in the tropics while we were out in Borneo – Shorea Faguetiania, 95.2m!