Landscaping For Hurricanes? - Sammy of Stone Marmot

Landscaping For Hurricanes

June 20, 2008

I went to the Bahamas a couple months after they were hit by Hurricane Floyd in 1999. The island I stayed on was originally covered with low (about 15 to 20 ft. high) trees. I don't know what kind of trees they were (probably a mix). These trees were densely packed together. The little space between them was usually filled with other vegetation. Consequently, you could not easily walk through a patch of these trees.

Sites for buildings were carved out amongst these trees. Because of how dense the vegetation was, little extra space, typically 4 to 12 feet, was cleared beyond the buildings.

This island was on the east side of the Bahamas and experienced winds of up to 150 miles per hour (mph) from Hurricane Floyd. Virtually every structure that stuck up higher than the tops of the trees or had direct water views to the east or south was severely damaged, if not totally destroyed. But virtually all the structures that were lower than the tops of the native vegetation had little or no damage. This is with 150 mph winds.

I've also noticed similarities in the damage from other places I've been to after major hurricanes (Homestead after Andrew, Punta Gorda after Charlie, southern Mississippi after Katrina, etc.). Most all the tall trees, billboards, street lights, power line poles, etc., tend to be broken or bent at approximately the same place, which is about 20 to 30 ft. above the ground. I suspect this is because the winds close to the ground have lower speed and more confused due to all the obstructions closer to the ground, compared to the winds higher up, which pretty much have a straight, unobstructed path.

Hurricanes contain absolutely unbelievable amounts of energy. But they do NOT possess infinite energy. Things in the path of hurricane winds do take energy from these winds. The more obstructions, the more energy taken from the winds and the more the winds are diverted.

This indicates that the more obstructions around your house, the more energy that will be removed from the winds, the lower the winds speeds, and the more the winds will be diverted. This assumes, of course, that the obstructions stay fixed in position and don't go flying around, otherwise they will just transfer their energy to whatever they hit, which will probably be your house. So you want low, dense, well rooted plants (and structures) around your house.

But this is not how most properties in the US are landscaped. Most properties have big grass lawns with a few (if any) token trees. Many times these trees are big trees, such as oaks and maples, which shade and overhang the house. This type of landscaping does little to protect places from hurricane winds. The grass lawns take almost no energy from the wind. Though the big trees do take energy from the wind, if they fall over or have major branches broken off, they will severely damage the house. This is why so many people in hurricane prone regions are scared of trees and clear all of them from their properties.

You really want lots of low trees and shrubs. Though I'm not an expert on plants, I suspect citrus trees, which generally are only 15 to 25 feet high, as well as podocarpus, southern red cedars, mangroves, and similar are much better suited and provide much better protection. You also want a lot of them so that their roots intertwine and they support each other and their branches share the wind load. This works best if most properties in a neighborhood are landscaped like this. The chances of a house surviving are also better if it is a single story cement block or brick house that has a hip roof (sloped on all sides, no gables) with protective covering for all the windows.

I admit that this is speculation based on my personal observations of areas affected by hurricanes. But internet searches and literature research shows almost no study of this possibility. More research needs to be done in this area. But those of us living in these areas can't wait for someone to eventually research it and need to act on the best knowledge presently available. It is very naive to think that the same type of house and landscaping styles that work for the Midwest and Northeast US are optimum or even desirable for the rest of the country.

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