The short answer to whether ice plant is invasive is yes, though the term refers to a group of plants. The most common and aggressively invasive species, known as highway ice plant or Hottentot-fig, is Carpobrotus edulis. This succulent perennial is a recognized ecological threat, particularly in coastal and Mediterranean climates. Its rapid growth allows it to overwhelm native ecosystems, and its intentional planting for ornamental purposes has led to extensive invasions across multiple continents.
Defining the Invasive Species
The confusion surrounding “ice plant” stems from its use as a common name for several species within the Aizoaceae family. The aggressive colonizer, Carpobrotus edulis, is primarily responsible for the negative ecological impacts. This species is distinguished by its fleshy, three-sided leaves and large yellow flowers that often fade to pink or purple.
The plant is native exclusively to South Africa, evolving in a climate similar to the California coast and the Mediterranean Basin. It was introduced in the early 1900s and widely promoted for soil stabilization and as a durable, drought-tolerant ornamental groundcover. Its success in these new environments was not contained, and it quickly escaped cultivation along railroad tracks, highways, and coastal dunes. Other non-invasive species, such as those in the genus Delosperma or Lampranthus, are also called ice plant, but they lack the destructive invasive potential of C. edulis.
Mechanisms of Ecological Domination
The success of C. edulis as an invader is rooted in an effective combination of reproductive strategies and physiological adaptations. It is a prolific clonal plant that spreads rapidly through vegetative propagation. Any stem fragment that breaks off and contacts the soil can re-root, leading to an ever-expanding mat of dense vegetation.
These mats can grow exceptionally thick, sometimes reaching 50 centimeters deep, effectively smothering native plants and blocking sunlight. Beyond clonal growth, the plant reproduces sexually, producing fleshy fruits consumed by small mammals like rabbits and deer. The passage of seeds through the animals’ digestive tracts enhances the germination rate, widely dispersing them away from the parent plant.
The plant’s succulent structure allows it to thrive in arid and semi-arid coastal zones due to high drought tolerance. This adaptation, combined with salt tolerance, gives it a competitive advantage over many native species. Furthermore, C. edulis hybridizes with native congeners, such as Carpobrotus chilensis, potentially creating more vigorous and adaptable hybrid invasive populations.
Environmental and Economic Consequences
The colonization by C. edulis results in measurable changes to the invaded landscape, leading to a significant loss of biodiversity. As the dense mats form, they create expansive monocultures that displace native flora. This eliminates habitat and food sources for specialized native insects, birds, and small animals, causing a break in the food web when native host species are replaced.
The plant also fundamentally alters the chemistry of the soil. As the fleshy leaves and stems die and decompose beneath the mat, they release high concentrations of organic matter, nitrogen, and salts. This process concurrently lowers the soil pH, causing acidification. This chemical legacy makes the environment unsuitable for the germination and survival of most native plant seeds, inhibiting natural ecosystem recovery.
Paradoxically, despite being introduced for erosion control, C. edulis can destabilize coastal dunes and bluffs. The plant possesses shallow roots that do not effectively bind the soil on steep slopes. Its heavy, water-logged biomass can contribute to soil slumping and erosion, especially during heavy rains. The widespread nature of these invasions necessitates expensive, large-scale control programs, incurring considerable economic costs for removal, chemical treatment, and ecological restoration.
Management and Non-Invasive Alternatives
Managing an invasion of Carpobrotus edulis requires sustained effort due to the plant’s high capacity for re-establishment. Manual removal is a common and relatively effective technique since the plant has shallow roots and is easy to pull up. However, it is labor-intensive for large areas, and all plant fragments must be removed from the site, as any piece of stem left can re-root and start a new infestation.
The removed material must be properly disposed of to prevent fragments from spreading or seeds from germinating. Disposal typically involves drying the material on an impervious surface or bagging it. For extensive infestations, chemical control using targeted, systemic herbicides may be necessary, but this must be done carefully to minimize impact on non-target species. Consistent monitoring is required for long-term management to detect and remove new seedlings or re-sprouting fragments.
Landowners and landscapers should choose non-invasive or native groundcovers to replace the ice plant. Native plants such as Salvia leucophylla (purple sage) offer excellent drought tolerance and erosion control while benefiting native pollinators and insects. Other suitable alternatives for coastal environments include native buckwheats or low-growing native succulent species that lack the aggressive growth habit of Carpobrotus edulis.