Sally Scalera

Brevard County Horticulture Extension Agent
3695 Lake Drive -- Cocoa FL 32926 -- 321-633-1702

Larger trees susceptible to storm damage

Oct. 15, 2005

One of our specialist’s, Dr. Mary Duryea with the University of Florida’s Reforestation and Urban Forestry Department, started researching a hurricane's effect on trees starting way back with Hurricane Andrew. A few weeks ago I heard Dr. Duryea give a presentation on what she learned about trees and hurricanes over the last nine hurricanes. (The ninth Hurricane was Dennis that hit the panhandle just this past July.) Here are some of the things that Dr. Duryea and her team have learned.

• The most damage done in the Panhandle from their four hurricanes was caused by laurel oaks that came down during the storms. Laurel oaks are fast growers but short lived. They are mature at 50 years old. They also have a light wood density and because of their large size are very damaging when they fall.
• Southern magnolias lost half of their leaves and even though they have light wood too, they stood up surprising well through the hurricanes. Southern magnolias live 100 years.
• Southern red cedars started to get ripped apart in winds of 100-125 mph and more.
• Slash pine and longleaf pine do pretty well in winds up to 130 mph.
• Sand pines start coming down early in a storm when the winds get to 85 mph. The message here is to not have any sand pines near the house. For that matter, loblolly pines are only a little bit better then sand pines so, don’t have them near a house, shed or car either. If a hurricane’s winds get to 145 mph or more, then pine trees will continue to die for months after the hurricane is gone even though they remained standing throughout the storm.
• The question “Why do large trees get damaged more then smaller trees” has three answers:
  1) there is an increasing loss of flexibility as the diameter of the trunk increases,
  2) wind speeds are greater as you get higher above the ground and
  3) fungal diseases can attack older trees.
• A clump or group of trees survived better then single trees planted out in the center of a landscape. This was true for all species of trees. The group of trees should have a minimum of five trees. (I will add an extra note here; the trees should also have ample rooting space or area within which to grow.)
• There is hard data (so far only for these two trees but that could change in the future) that proves preventative pruning (thinning) does improve the survival of live oaks and gumbo limbo through hurricanes.
• Appropriate rooting space improves survival. A large tree planted in a large area will have enough room for the roots to spread two to three times past the end of it’s branches (this is the normal root system of a tree) and will be able to hold itself up in a storm. A large tree planted between the street and sidewalk is more likely to eventually be blown over in a storm. A small tree planted between the curb and sidewalk is much more likely to still be standing after a hurricane.
• Here are some species of trees that Dr. Duryea found did poorly through the hurricanes; Australian pines; older trees of laurel, water and turkey oak; Chinaberry; Ficus benjamina; Southern red cedar if it had more than one main trunk (which we call multiple leaders); W. Indian mahogany with multiple leaders and carrotwood.
• Here are some of the best wind resistant trees (assuming all production, planting, design and maintenance practices were done correctly); live oak, Southern magnolia, bald cypress, hollies, gumbo limbo, sycamore and green buttonwood.

  Here are the characteristics that make a tree more resistant to hurricanes:
  Strong wood: species with higher wood density survived better and lost fewer branches.
  Defoliates early: leaf loss is positively correlated with survival.
  Strong roots: root density is correlated to wood density.