Invasive plant species, like the devil's claw, are often managed intensively — but are they harmful?

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Conservationists and land managers should no longer use the origins of plant species as a guiding principle for policy and management decisions, argues a team of ecologists led by Marc Davis. Instead, they should focus on the function of plant species and whether they benefit or threaten biodiversity, human health, ecological services and economies.

The idea of plant 'nativeness' was introduced in the mid-19th century, leading to the discipline of 'invasion biology' in the 1990s. But there is little evidence to support the claim that non-native species are the "enemies of man and nature", say the authors. In fact, recent research suggests that alien species can be beneficial as they tend to increase the number of species in most environments, for example.

The effects of non-native species may change over time: species that are not causing harm now, may do so in the future. But this is no different for native plants, they say.  And many of the species thought of as native are actually alien.

"Nativeness is not a sign of evolutionary fitness or of a species having positive effects," write Davis and colleagues. But the claim has led to conservation efforts that make little ecological or economic sense. For example, the devil's claw plant, introduced from Mexico to Australia, is managed intensively — yet there is no evidence that it reduces biodiversity.

Plans to eradicate alien plant species are often ill-fated, say the authors. Instead, "we must embrace ... 'novel ecosystems' and incorporate many alien species into management plans", which should take into account the positive effects of non-native species.

Conservationists and governments should still tackle problems caused by non-native species, but management plans should be based on empirical evidence and scientists have a responsibility to convey the benefits of alien plant species, the authors conclude.

Link to full article in Nature