invasive species

Mangroves are beneficial and thus were not among the “exotic” species we studied during Week 12 of the Master Gardener Program. These red mangroves, which grow along the coast, are sometimes called “walking trees” because of the prop-roots they put out. / Amanda Gorney, taken at Dr. Von D. Mizell-Eula Johnson State Park in Dania Beach


As I go into the final weeks of my Florida Master Gardener Program, I realize that we’ve spent an awful lot of time studying problem plants and harmful pests — insects, snakes, rodents and the like.

But as one of our venerable instructors — John Pipoly, Ph.D. — stresses, pests are one of our biggest challenges, so we need to know how “to find, identify and eliminate them.”

During Week 12, among the educational materials we used was his 30-page booklet Invasive Species: Policy and Biology. Dr. Pipoly is an urban horticulture extension agent for the University of Florida’s Institute of Food and Agricultural Sciences’ Broward County Extension.

Invasive Brazilian Pepper Tree / invasive species

The invasive Brazilian pepper tree produces fruit that birds eat. As birds travel and expel the seeds, the trees proliferate. / Courtesy Dr. John Pipoly

An invasive species — also called, ironically, “exotic” — is one that is introduced, accidentally or purposefully, into an ecosystem in which it did not evolve. As you might guess, this isn’t good.

Invasive species harm natives

One of the problems is that exotic species displace native ones. But there are other problems with invasive plants. For example, they grow and mature rapidly due to their high photosynthetic rates; they reproduce very efficiently, thanks to their prolific seed production; and they have small, easily transported seeds that are spread via long-range dispersal mechanisms – often by birds.

Another problem: allelopathy. Non-natives can produce chemicals that inhibit the growth of other plant species around them.

Not that native species are entirely benign, according to Dr. Pipoly: “We used to think that natives used less water, and that there would be less need for fertilizer, and that they were subject to fewer pests. But research results show none of those concepts are true.”

Seagrape / invasive species

The seagrape is native to Florida and produces berries that, once ripe (they’re turn almost a burgundy color), can be eaten right off the tree. / Amanda Gorney

And here’s a sobering statistic: 400 of the 958 federally endangered species are affected by invasives.

Some of the bad …

Among the invasive species is the Brazilian pepper tree. Introduced as an ornamental, it now cover 900,000 acres in the Sunshine State, and its sap irritates the skin.

And who hasn’t smelled the exotic melaleuca, introduced — on purpose — from Australia in the very early 1900s. The goal of those who imported it was to drain the Everglades and therefore allow more space for development.

Unfortunately, the trees do an excellent job of invading freshwater wetlands and reproducing: A single tree produces up to 20 million seeds per year. The flowers have a characteristic potato-like smell that can cause respiratory problems in some humans. Despite an ongoing eradication program, melaleuca trees still cover about a half-million acres in the Everglades.