Hurricanes Bring Environmental R

Hurricanes Bring Environmental Renewal

Kelly Schweitzer

Psychology Major

Hurricane Ivan

Hurricanes form in tropical regions where there is warm water (at least 80 degrees Fahrenheit / 27 degrees Celsius), moist air and converging equatorial winds. Most Atlantic hurricanes begin off the west coast of Africa, starting as thunderstorms that move out over the warm, tropical ocean waters. A thunderstorm reaches hurricane status in three stages:

Tropical depression - swirling clouds and rain with wind speeds of less than 38 mph (61.15 kph / 33 kt)

Tropical storm - wind speeds of 39 to 73 mph (54.7 to 117.5 kph / 34 to 63 kt)

Hurricane - wind speeds greater than 74 mph (119 kph / 64 kt)

It can take anywhere from hours to several days for a thunderstorm to develop into a hurricane. Although the whole process of hurricane formation is not entirely understood, three events must happen for hurricanes to form:

A continuing evaporation-condensation cycle of warm, humid ocean air
Patterns of wind characterized by converging winds at the surface and strong, uniform-speed winds at higher altitudes
A difference in air pressure (pressure gradient) between the surface and high altitude

Warm, moist air from the ocean surface begins to rise rapidly. As this warm air rises, its water vapor condenses to form storm clouds and droplets of rain. The condensation releases heat called latent heat of condensation. This latent heat warms the cool air aloft, thereby causing it to rise. This rising air is replaced by more warm, humid air from the ocean below. This cycle continues, drawing more warm, moist air into the developing storm and continuously moving heat from the surface to the atmosphere. This exchange of heat from the surface creates a pattern of wind that circulates around a center. This circulation is similar to that of water going down a drain.

Track a Hurricane

Converging winds" are winds moving in different directions that run into each other. Converging winds at the surface collide and push warm, moist air upward. This rising air reinforces the air that is already rising from the surface, so the circulation and wind speeds of the storm increase. In the meantime, strong winds blowing at uniform speeds at higher altitudes (up to 30,000 ft / 9,000 m) help to remove the rising hot air from the storm's center, maintaining a continual movement of warm air from the surface and keeping the storm organized. If the high-altitude winds do not blow at the same speed at all levels -- if wind shears are present -- the storm loses organization and weakens.

High-pressure air in the upper atmosphere (above 30,000 ft / 9,000 m) over the storm's center also removes heat from the rising air, further driving the air cycle and the hurricane's growth. As high-pressure air is sucked into the low-pressure center of the storm, wind speeds increase.

ECOLOGICAL SUCCESSION

Ecological succession is the natural process of establishing or reestablishing an ecosystem.

Succession occurs as a series of plants, animals, and microbes colonize a site over time.

Succession may occur on sites that were previously unoccupied or on sites at which the exiting biotic community was removed or altered by disturbance.

Primary succession occurs on sites that have not been previously occupied. Such sites exist on newly formed soils, such as exposed sandbars and volcanic ash. The colonization of a sunken ship by coral reef organisms is an example of primary succession.

Secondary succession occurs when a biotic community has been disturbed, then becomes reestablished. Remnants of the previous biotic community still exist at the site and contribute to recolonization. Secondary succession is much more common than primary succession; much of the landscape is in a stage of secondary succession. One common example of secondary succession is the reestablishment of forest vegetation after an area has been logged. When a forest is logged, only the merchantable timber is removed, undesirable tree species, shrubs, saplings, and seeds remain and constitute the colonizer pool.

Forest Succession

Forest ecosystems, even in the absence of disturbances from human activity, are not static and unchanging. These landscapes are dynamic and change in response to variations in climate and to disturbances from natural sources, such as fires caused by lightning strikes. Ecosystems respond to disturbances through a natural process called succession, a recovery process that occurs in predictable stages. After a fire burns down a swath of woodland, a sequence of ecological responses begins. There is a quick flourishing of “pioneer species” amid the charred forest remains, usually quick-growing grasses and weeds, followed by a steady advance of slower-growing, taller species of plants. The first trees to emerge are often small pines, followed by larger pines and finally by hardwood species such as oak and hickory. This process begins quickly but it can take decades or even hundreds of years for a forest ecosystem to move from its early “pioneer” stage to its “climax” stage.

Hurricanes blew through many parts of the world, bringing with it torrential rains and microbursts of 80 miles per hour. The hurricane caused extensive damage throughout the forests. In several sections of in the forests, over 80% of the canopy trees were blown down.

A number of factors caused some trees to fall while others remained standing. Most of those that fell were broadleaf deciduous species, commonly referred to as "hardwoods". These trees have broad spreading canopies and flat leaves which caught the force of the wind much more readily than the smaller canopies and aerodynamic needles of pine trees. Many hardwood trees also have shallow, spreading root systems, which increased their susceptibility to tip ups, versus pines, which have the deep tap roots holding them upright.

Note that many more trees toppled than snapped or broke. Because there was a large volume of rain in the days prior to the hurricane, the soil was saturated by the time the hurricane arrived. Tree root systems were easily separated from the soft soil, readily allowing the wind to knock the trees down.

The topographic position of a tree also effected its likelihood of falling. Much of the hurricane damage was concentrated at topographic extremes; particularly hard hit were stream bottoms (having the wettest soils) and ridge tops (having the greatest exposure). In addition, because the winds were coming primarily from the northeast, tree stands on slopes facing in those directions were also more heavily damaged.

Although the damage from Hurricane appears to be catastrophic, disturbance is a natural part of forested ecosystems -- the forest will recover. Take notice of the some of the ways the forest is naturally recovering from hurricanes:

3) growth of suppressed tree saplings into canopy gaps. Note that animals are taking advantage of this new growth by eating new tender sprouts

Succession is a change in plants and animals which occurs periodically in all communities. An open space or meadow will eventually be overgrown by a forest which in turn will grow to a climax forest. The length of time and kinds of plants involved in each successional change depends on many factors. The successional progression can be changed at any stage by many different factors and disturbances. These factors and disturbances have negative and positive effects on succession. Disturbances in the forest can be human made or natural.

Terms:

Coriolis force: the apparent force resulting from the earth's rotation that deflects moving objects to the right in the northern hemisphere and to the left in the southern hemisphere.

Cyclone: a storm or system of winds that advances 20-30 mph and rotates around a center of low atmospheric pressure in a direction counterclockwise in the northern and clockwise in the southern hemisphere.

Hurricane: tropical cyclone with maximum sustained surface winds of at least 74 mph (64 knots).

Knot: a measurement used to measure the speed of a ship; equals one nautical mile per hour (1.15 mph or 1.85 kph).

Storm Surge: An abnormal rise of the sea along a shore caused primarily by the winds of a storm. Storm Tide: The rise in water levels as a result of both the storm surge and normal tide action.

Tropical Depression: A tropical cyclone with maximum sustained surface winds less than 38 mph (33 knots).

Tropical Disturbance/Tropical Wave: An unorganized mass of thunderstorms with very little, if any, organized wind circulation.

Tropical Storm: A tropical cyclone with maximum sustained surface winds ranging from 39-73 mph (34-63 knots).

Most hurricanes happen between June 1 and November 30. Warmer water temperatures are one reason there are more hurricanes in the summer.

Some years there are many hurricanes and some years there are very few. Wind and rain patterns from all over the globe also affect how many hurricanes there are each year.

The whirling storms that blow across the north Atlantic and the Caribbean Sea are called hurricanes after a Carib Indian word for "big wind."

Storms that form in the Indian Ocean are named cyclones. The name, based on a Greek word meaning "coil," describes the spiraling winds.

Storms that spring up from the western Pacific ocean are called typhoons, after the Chinese words for "great wind."

National Research Council. 1992. Restoration of Aquatic Ecosystems. National Academy Press, Washington, D.C. 552 pp.

Restoration Ecology. 1993. Blackwell Science. A peer-reviewed scientific and technical journal published quarterly and available through the Society for Restoration Ecology.

Restoration and Management Notes. 1981. Published twice yearly by the University of Wisconsin Press for the Society of Restoration Ecology; nontechnical.

Thayer, G.W. (ed.). 1992. Restoring the Nation's Marine Environment. Maryland Sea Grant College, College Park, Maryland. 716 pp.

Bio-physical Factors	Natural Disturbances	Human-Made Disturbances
climate	volcanic activity	plowing and grazing
water sources	insects	tree harvesting
weather	fire	road building
topography	wind storms	soil erosion
soil composition	flood	introduced species
wildlife	soil erosion	prescribed fire

Forest Succession

Patterns of Hurricane Damage

Terms: