A super weed - the invasion of tropical rainforest by a shade-tolerant shurb

What is it about?

The National Weeds List in Australia informs the public and land managers on weeds prioritized for management, but shade-tolerant weeds that can invade forest ecosystems are inadequately listed. Such weeds are now globally recognized for their ability to impact native vegetation. The Cherry Guava (Psidium cattleianum) from Brazil, a shrub of the Myrtle family (Myrtaceae), is an exceptional example. 1. Cherry Guava was probably introduced to Australia for its edible fruits. The earliest record (1940s) was in Koah, Far North Queensland. Currently, Cherry Guava infestations are found in three World Heritage Areas in Australia: the Wet Tropics in Queensland; Gondwanan Rainforests of Queensland/New South Wales, and Lord Howe Island. It is listed as a noxious weed only in NSW. There are no Australian regulations restricting import or sale. 2. The Global Invasive Species Database lists Cherry Guava among the World’s 100 Worst Weeds – it tolerates shade; grows and matures rapidly; produces a heavy fruit set and seedling bank; is spread by native and feral animals; coppices extensively; and forms multi-stemmed thickets. It can displace native vegetation. Infestations in Australia appear free of natural enemies and resistant to Myrtle Rust which affects co-occurring native members of the Myrtaceae. In Hawaii, Seychelles and Mascarene Islands, natural forested ecosystems are severely impacted after introductions in the early- to mid-1800s. 3. Cherry Guava spread is ongoing, but given the recent Australian history and localized infestations, eradication may be possible with incisive intervention. Government listings and restricting import and sale are first steps. Options to eliminate infestations could combine ecotourism, volunteers and biological control agents.

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Why is it important?

Environmental weeds typically invade open, disturbed areas or vegetation edges, and can have devastating ecological and economic consequences. We need to understand how shade-tolerant weeds can affect forest ecosystems to better manage such invasions.