Fifty-seven major hurricanes (winds greater than 110 mph) have struck the United States on an average of twice every three years between 1899 and 1983. Several of these storms have inflicted catastrophic losses to the urban vegetation of Atlantic and Gulf Coastal Communities. Extreme examples are provided by the Labor Day Hurricane of 1935 which wiped out a 40-mile section of the Central Florida Keys and the New England Hurricane of 1938 which destroyed one million shade trees.
The challenge of reducing storm-related damage to plant material is compounded by a relatively low frequency of tropical storms during the past 15 years. Many communities have become too complacent with the result that little has been done in the area of hurricane-plant management.
Fortunately, several important strategies can be adopted before and after a hurricane strikes to reduce damage in the landscape. Before the hurricane season each landscape should be surveyed to identify dangerous trees that could pose a threat to life and property (Tables 1, 2, 3, and 4). The most dangerous tree is one that is tall, densely crowned, and has repeatedly performed poorly in past storms. In established landscapes, consideration should be given to removing dangerous trees while leaving or planting the tough ones.
Resistance of species to hurricane-related damages* (in descending order of resistance).
Twelve potentially dangerous South Florida trees (as identified by Fontana, 1981).
Recommended trees for South Florida (as identified by Siegendorf, 1981).
Performance of shade trees in New England Hurricane 1938 in descending order of resistance (from Chadwick, 1939).
The greatest measure for reducing breakage and windthrow of trees involves pruning. The concept is to reduce the surface area of a tree, allowing more wind to pass through. Pruning should allow 10-25% of sunlight to pass through small and young trees and 25-40% of sunlight through large trees. Greater movement of wind through the crown can be facilitated by thinning horizontal limbs so that remaining ones have a spacing of 16-18 inches. Reducing a tree’s height can seriously disfigure a tree. No more than 20-30% of a tree’s top should be removed.
Keep in mind that not all trees are amenable to pruning because of their shape. As a general rule, trees with columnar habits are less amenable to pruning. The pines, sycamore, and Italian cypress are a few of the specimens that display this habit. During pruning operations, large fruit such as coconuts should be removed since they can become airborne and damage structures in high winds. Pre-hurricane pruning practices should be repeated every 4-5 years. Figure 1 illustrates the proper method of pruning mature trees to reduce wind damage.
Severe hurricanes of the 20th Century. Fifty-seven major hurricanes have affected the U.S. since 1899 — an average of two strikes every three years.
One does not have to be a prophet to know that this tree was a prime candidate for windthrow. In fact, it blew over like a matchstick in a thunderstorm in which winds reached 40 mph (estimated). Note absence of root system. Trees which are seriously stressed due to construction damage, insects or diseases should be removed to protect life and property.
Tall, densely crowned trees with little taper are prime candidates for breakage and windthrow in hurricaneforce winds. Each landscape should be surveyed to identify “dangerous” trees that could pose a threat to life and property (see tables). Consideration should be given to removing dangerous trees if they are within striking distance of a building.
The effects of salt spray may be felt anywhere from a few miles to 40 or 50 miles inland. Salt damage was experienced as far inland as 45 miles following the New England Hurricane of 1938. Leaching root systems and watering foliage will help minimize salt damage. Photo credit: American Red Cross; hurricane of September 1947, Miami Beach, FL.
Trees that are declining due to disease or insect attack are subject to storm damage and should be removed. For example, pines are most likely to snap where fusiform rust galls are located. In some trees, decline can be identified by observable symptoms (i.e., presence of galls) while in others it may not be readily apparent (i.e., internal wood decay).
Following hurricane conditions, quick action needs to be taken to rescue damaged trees and plant material. Various opinions exist on the potential for rehabilitating uprooted and leaning trees.
At least 4 factors should be evaluated before a decision is made to save a damaged tree: sentimental value, growth rate, condition, and transplantability. If a damaged specimen has sentimental value, the homeowner may be willing to take the chance and incur the expense of saving it. Fast growing trees tend to be short lived and it may not be worthwhile resetting them. Damaged trees already declining due to insects or disease should be removed. Various species have root systems that do not transplant well, hence they too should be removed.
If the decision is made to save a windthrown tree, every effort must be made to protect the exposed root system and prevent it from drying out. Mud, moist burlap sacks, or sphagnum moss can be put on exposed roots until the tree is reset. Damaged roots should be removed so that a tree can be reset at ground level.
Satisfactory rehabilitation depends on a proper balance between the crown of a tree and its roots, so approximately 20-30% of the above ground portion should be pruned. Once the tree is in an upright position, the soil should be compacted somewhat to prevent air pockets. A water basin at least 3 feet in diameter and 6 inches high should be constructed around the tree to encourage infiltration and percolation to the immediate root area.
Trees that have been defoliated by high winds should be saved as most specimens will refoliate. These trees, as well as those severely pruned, should be protected from sun scald and moisture loss. White water based vinyl, latex or acrylic paints have proved to be effective, nontoxic, and durable and can be painted on the main stem.
Once reset, trees should be supported by guying and staking. Trees two inches or less in diameter can be supported by a 2 × 4 inch stake extending up to the first whorl of branches. Stakes 8 feet tall should be attached to a tree by a wire which is run through a piece of hose. Trees larger than 2 inches are supported by three guy wires attached to stakes driven in the soil.
Despite the fact that many trees and shrubs remain upright following the storm, they may have been tossed back and forth creating a hollowing of soil near the primary trunk at ground level. Additional soil can be added to this area and compacted around the plant to eliminate air pockets.
Following the storm, trees should be watered at least once every 5 to 7 days. Fertilizing should be delayed 3 to 4 months. Fertilizing trees with damaged roots may interfere with water uptake and cause physiological damage to a tree.
Standing trees will often experience moderate to severe breakage and several wounds during hurricanes. Severe pruning will be necessary to remove damaged and weak branches. Bark injuries should be treated immediately. Damaged and isolated scraps of bark should be removed. Reshaping the wound to conform to an elipse will promote healing. The wound surface should be smooth with all splintered wood removed. Orange shellac, commercial tree paints, grafting waxes, and house paints are a few of the materials that are often applied to wounds.
Salt damage can result from inundation from the storm surge but is more likely to result from wind-driven salt spray. The following guidelines should be followed to minimize salt damage following storms:
Foliage and branches should be washed with a stream of water to remove salt, mud, and debris.
On porous soils, leaching of the salt can be accomplished by building a basin 3 to 4 inches deep around the plant or bed. Fill the basin, allowing water to remain no longer than three hours during the cooler part of the day (to minimize evaporation). This process should be repeated several times.
Surface soil that has been eroded can be replaced if the landowner can afford it. This practice is limited to small ‘prize’ shrubs.
Trees and shrubs that have incurred salt damage should be watered every third day.
In summary, while there is no way of preventing loss caused by hurricanes, following the recommendations stated and adopting those arboricultural practices that promote healthy trees will go a long way toward minimizing losses.
- © 1984, International Society of Arboriculture. All rights reserved.
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