Invasive Alien Plants: not from Mars, but controversy brews over source of introduction

Botanical gardens - those quiet sanctuaries where folks go to stroll amongst flower and trees, contemplating the fate of the world - or escaping from it for a few precious minutes. Not exactly a place that you would consider as a hotbed of invasive species activity, now would you?

Well, it may not be that extreme but Philip Hulme, a weed specialist at Lincoln University, New Zealand, claims that a large number of invasive plant species can be traced back to botanical gardens or arboretums. Hulme reviewed the history behind 34 of the top 100 invasive plant species as defined by the IUCN. Researching the origins of these plants, Hulme found that over half of them could be traced to botanical gardens. From a horticultural laboratory or garden, winds, temperature, and animals that can distribute seeds - all can play a role in allowing an alien species to gain a foothold.

Just what are we talking about when we say "invasive plant species"? Well, it casts a fairly broad net, ranging from weeds and vines to flowers all the way to large trees. In the right climate and soil environment, many have the ability to propagate quickly and literally push indigenous plants out of the way. This has often happened when exotic tropical plants have been brought into non-tropical forest environments - the tropical plant comes from an ecosystem where many different plant species are thrust together and battle it out for territory. In less competitive environments, these species can quickly dominate.

As expected, the botanical garden community is not particularly pleased with Hulme's research and conclusions. Stephen Blackmore, head of the Royal Botanic Garden Edinburgh, U.K., says that while botanical gardens may have been interested in introducing non-native species - but lax in protocols - in the past, today they are much more mindful of the consequences and that it is home gardeners and the horticultural trade that probably deserve greater inspection.

"I am not saying that that lets botanic gardens off the hook," says Blackmore, adding that botanical gardens today go to great lengths to quarantine new plants to guard against the spread of fungus or disease, and that they are very conscious of preservation and conservation of the local botanical ecology. Botanic Gardens Conservation International, a global network of botanical gardens, is beginning to develop a set of guidelines for how alien or non-native plants should be managed.

Home gardeners and commercial plant shops remain as a possible point of introduction of invasive species, much like the tropical fish stores and home aquarists who thrill at displaying tropical fish and seaweed species until they become to large or too aggressive for the tanks they are in and accidentally end up in local waters, disrupting the balance of an ecosystem. Case in point, the Caribbean invasion by the voracious lionfish, a Pacific Ocean species.

As mankind becomes more and more global in his curiosity and his movements, then the threat of disruption of ecosystems by invasive species - whether accidental or by design - remains high.

Read more about invasive plant species in NatureNews.