Botanic gardens: plant oases or invasions waiting to happen?

A relaxing stroll in a botanic garden sounds like a lovely way to spend an afternoon. These green oases can encourage people to appreciate nature and bring attention to conservation issues. But some botanic gardens might harbor an ecological threat: they could be prime sources for invasive species to spread into the wild.

Some might argue that the gardens don’t present much of a threat. While botanic gardens have unleashed invasive species in the past, many now take care to avoid cultivating invasive plants or to keep such plants contained. “This greater emphasis on conservation priorities and awareness of plant invasions may result in living collections posing a negligible risk to the environment,” writes Philip Hulme, a researcher at Lincoln University in New Zealand, in Conservation Biology. “But is this the case?”

To find out, Hulme turned to the PlantSearch database, which contains more than 1 million records on 3,082 botanic gardens worldwide. He tried to determine how frequently non-native and threatened plant species were cultivated in gardens. Hulme also searched another database, as well as botanic gardens’ websites, for information about whether the gardens had taken steps to prevent invasions.

Botanic gardens provide a refuge for some struggling plants: they contain about a quarter of threatened plant species. But they also hold 99 percent of major invasive species, Hulme found. He estimates that an average botanic garden might house 26 invasive species. And less than 10 percent of the gardens have an invasive species policy.

Because the average collection size and the fraction of non-native species in gardens has shrunk in the last century and a half, the risk that a new garden will release an invasive plant has dropped by 90 percent. But botanic gardens have become much more common, especially in Asia and South America; there are now more than 10 times as many gardens worldwide as there were in 1900. So overall, says Hulme, the risk hasn’t changed much. Roberta Kwok | 4 December 2014

Source: Hulme, P.E. 2014. Resolving whether botanic gardens are on the road to conservation or a pathway for plant invasions. Conservation Biology doi: 10.1111/cobi.12426.

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