An exotic plant is defined as a plant species that is not native to an area in which it is growing.
Not all exotic plants introduced are a problem. When an exotic plant exhibits "aggressive" and "competitive" behavior that disturbs the species composition of an ecosystem by crowding out and replacing native species it becomes a problem. An exotic plant exhibiting this form of behavior is characterized as an invasive exotic.
Another group of exotic plants are those that have undesirable characteristics such as unstable root systems (e.g. Australian Pine) or brittle wood (e.g. Indian Rosewood). These plants are referred to as nuisance plants and often pose a public safety hazard.
Of the nearly 25,000 exotic plants that can be found in Florida only a small number (< 1%) are classified as invasive or nuisance exotics. Unfortunately, this small number of exotics causes significant damage to intact ecosystems resulting in widespread habitat destruction at an alarming rate. In addition this small group of plants (and animals) comes with a large price tag. During the fiscal year 1999 - 2000 ten state agencies spent nearly $91 million on the eradication of invasive plant and animal species in Florida.
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Generally invasive exotics have some form of competitive advantage over native species. This advantage can be in the form of a faster growth rate, which can literally leave slower growing native plants in the dark and unable to grow. In some cases the invasive exotics are better at utilizing available resources such as water leaving native plants high and dry.
The dominance of one plant species in an ecosystem is reflected in the loss of diversity and the increase in endangered species. The effect of exotics on an ecosystem is not limited to plants but rather trickles down the food chain. A loss of native species can lead to the total elimination of important food sources for plant eating animals. This in turn will lead to reduced food sources for carnivores, which will either move on to intact ecosystems (leading to overcrowding in the new area) or simply die due to lack of food.