Florida brought in Old World climbing fern as an ornamental; the vine later smothered more than 100,000 acres and can carry ground fires into tree canopies

A plant that was once deemed appropriate for the decoration of gardens has turned out to be a significant problem in Florida’s natural habitats. Old World climbing fern does not stay low to the ground like many ornamental plants. It doesn’t lie down on the ground but rather climbs up trees and spreads across bushes and creates dense layers of plants that can cover a significant area of forest. The U.S. Department of Agriculture (USDA) states that the threat is not limited to plants that it covers. The fern can also make it easier for fire to reach tree canopies, turning flora that may otherwise have escaped the fire into fuel for active fire. The degree of its spread is so extensive that dozens of thousands of acres of land in Florida are reported to be affected.

A nursery plant found a way into the wild

The fern is indigenous to tropical and subtropical regions of Africa, Asia, and Australia. It was introduced as an ornamental plant for its foliage and for its climbing habit in the USA. The first record in Florida occurred in 1958 when a plant was grown at a nursery in Delray Beach. By 1960, it was also being collected while growing in the wild in Martin County. The fern had already become established in South Florida and was suffocating native shrubs and other low-growing plants by 1978. It was hard to control because it is carried by the wind and produces small spores. A single fertile leaflet can produce as many as 28,600 spores, giving the plant many chances to establish itself in new places. The long, slender fronds of the fern compound the issue. They can reach a height of 90 feet and spread out over the ground, around shrubs and into tree branches. Its spreading growth creates dense mats that block the light from reaching the vegetation below.


Why the fern makes wildfires more dangerous

The damage goes beyond the plant’s growth. Old World climbing fern can alter fire behaviour in a natural area. Fire in a forest will usually be low to the ground. However, if the fern grows on trees, it forms a ladder for fire to move up the trunk. The vines can carry flames into tree crowns, allowing fire to reach branches and leaves that might otherwise escape a ground-level burn. The USDA describes this as a fire-ladder effect. This creates an added challenge for land managers. A fire that reaches the canopy can damage or kill trees and affect the habitats they provide for wildlife.

Why removing the fern is difficult

Land managers have used herbicides and mechanical removal to control the plant. However, both approaches have limits. Herbicides must be applied carefully to avoid harming nearby native plants, while removing the fern from remote or difficult-to-reach areas can be expensive. Even killing the visible growth does not immediately restore the affected land. Dead vines can remain draped over trees and spread across the forest floor, leaving thick layers of plant material behind. Meanwhile, spores may spread to outside of treated areas and cause new infestations. The University of Florida states that the spread of the fern into remote areas hinders its control. Therefore, some scientists have been searching for methods to manage the fern through biological control methods such as insects that are natural enemies of the plant.

Can insects slow the invasion?

The native Old World climbing fern is consumed by several caterpillars in its native habitat. Researchers have investigated these insects to see if they can be used to control the growth of the fern in Florida. One of the insects that they studied was a moth called Neomusotima conspurcatalis, which is called the brown lygodium moth. It is host-parasitised by its caterpillars. Caterpillars of the ferns were caught and identified in Southeast Asia, and their physical characteristics and stages of development were examined. The immature stages of some of the moths were not previously described by science. Later, the brown lygodium moth was accidentally introduced in Florida and is considered to have contributed to the slow spread of the fern. It provided some additional tools to land managers besides traditional removal techniques.

The science of selecting the right predator

Using insects to control an invasive plant requires care. A species that feeds on the target weed must not become a new threat to other plants. It is not only important to know what an insect eats, but also how it interacts with other organisms in the environment. USDA scientists and Florida collaborators have continued to study interactions between the moths and parasites, predators, and fungi. They are important because an insect's survival and control of a plant may depend on more than its appetite. In Florida, where the fern has already been found to be present in a large amount of natural habitat space, that balance is a key component of preserving the landscapes it has taken over.