Invasive species & rewilding

An invasive species is a non-native organism introduced to a new environment where it spreads rapidly, outcompetes native species, and causes ecological or economic harm. Not all introduced species are invasive — most fail to establish. But those that do succeed in novel environments can rapidly alter habitats, predator-prey relationships, and soil chemistry in ways that native biodiversity cannot adapt to quickly enough. Invasive species can be plants, animals, fungi, or microorganisms.

Rewilding depends on allowing natural ecological processes to unfold. Invasive species disrupt those processes in a number of ways including by altering fire regimes, soil chemistry, hydrology, and food webs. An invasive grass species that changes fire frequency can prevent forest regeneration. An invasive predator can drive endemic prey species to extinction before any rewilding intervention can succeed. Managing invasives is not optional in rewilding: it is often the prerequisite that determines whether ecological recovery is possible at all.

In some cases you can, particularly in passive rewilding scenarios where native species are still present and capable of competing. In other cases, reintroducing large herbivores can naturally suppress invasive plants through selective grazing. However, research increasingly shows that the most successful restorations integrate invasive species management with native species establishment simultaneously, rather than treating them as sequential phases. Removing invasives without planting natives often just creates an open niche that a different invasive rapidly fills.

It depends heavily on the species, ecosystem, and scale of invasion. Prevention remains the most cost-effective approach — stopping invasive species from establishing is far cheaper than controlling or eradicating them once established. For established invasions, mechanical removal, targeted herbicide application, biological control (introducing natural predators or pathogens from the invasive's native range), and restoration of competitive native vegetation are all used depending on context. Integrated approaches that combine multiple methods consistently outperform single-method strategies.

Some of the most significant include: Japanese knotweed, which outcompetes riparian native plants and destabilizes riverbanks; buffelgrass and cheatgrass, which alter fire regimes in arid western ecosystems making them more prone to intense fires that kill native species; feral pigs, which root up native vegetation and destroy ground-nesting bird habitat across the Southeast and West; brown-headed cowbirds, which parasitize native songbird nests; and invasive carp species, which devastate aquatic ecosystems. In Texas specifically, King Ranch bluestem and buffelgrass are major threats to native grasslands.

The most impactful actions are: identify and remove invasive ornamental plants (many garden centers still sell species that are invasive in the wild — check your regional invasive species list); replace them with regionally native alternatives; avoid moving soil or mulch that might carry invasive seeds; clean boots, tools, and equipment when moving between sites; and report unusual invasive species sightings to your state or county invasive species program. Every garden that converts from invasive ornamentals to native plants strengthens the local ecosystem a little more.