Invasive species kill native plant species

The argument

Invasive plants do not merely join an ecosystem; they displace the plants already in it. The Kudzu vine is the standard illustration: it can grow roughly thirty centimetres in a day, and at that rate it simply grows over whatever is beneath it, blanketing shrubs, saplings and ground cover until they are deprived of light. A plant that cannot reach light cannot photosynthesise, and a plant that cannot photosynthesise dies. Because the vine spreads faster than the native species can compete, the outcome is not a mixed community but the replacement of one community by another. The harm to animals follows from what native plants do for them. Native plants are the base of the food web in the places they grow, and the animals around them have adapted to those particular plants as food, shelter and breeding habitat. Specialist feeders are the most exposed: an animal that depends on one kind of plant has nowhere to go when that plant is choked out. Generalists fare better but still lose part of their forage. When the plants at the base of the chain are removed, the organisms that rely on them starve, and the predators that rely on those organisms lose their prey in turn. This is why the argument treats damage to plants and damage to animals as the same harm rather than two separate ones. An invasive plant need never touch an animal to kill it; it only has to remove what the animal lives on. The loss moves upward through the ecosystem from the bottom, which is both why it is hard to see early and why it is hard to reverse once the native plant community is gone.

Premises

Counter-arguments

Some invasive plant species benefit an ecosystem. In California, California butterflies lay eggs on an invasive eucalyptus tree because of the deforestation of native trees. Some invasive species are useful and help animals to thrive among depleting habitats.

Rejecting the premises

[Rejecting P1] Not all invasive plants kill native plants.