Alien invasion of the inner space

Strawberry guava (Psidium cattleianum) is considered among the world’s top 100 worst invasive alien species. It is a shade-tolerant woody weed with the ability to impact intact rainforest communities. Strawberry guava, native to eastern Brazil and north-eastern Uruguay, has had a devastating effect on native habitats in Mauritius and is considered the worst plant pest in Hawai'i, where it has invaded a variety of natural areas

The aims of the research project by Tng et al were to:

  • characterise the demographics of strawberry guava populations across rainforest sites of different stages of successional   development
  • compare various community and site attributes between strawberry guava -invaded and non-invaded sites
  • model strawberry guava invasive traits in relation to these attributes.

A successional chronological sequence of regrowth rainforest sites ranging in age from 3 to 69 years were compared to a cross-section of primary rainforest sites on the southern Atherton Tableland.

Strawberry guava invasion was found to be restricted to secondary successional forests where it represented 8% of all individual stems and 20% of all seedlings recorded. It also had the highest basal area among all non-native woody species present.

Their analysis showed that strawberry guava is able to establish and persist under a closed rainforest canopy and that the species embodies a wide range of traits that facilitates it invading rainforest. These traits include: a high relative growth rate; extremely abundant fruit and seed set; the ability to coppice and re-sprout; an ability to form dense thickets; and widespread dispersal by fauna.

Strawberry guava invasion of primary rainforest was not detected, suggesting that primary rainforest may have some resilience to invasion. Contrary to expectation, the age of the secondary forest did not influence the number of strawberry guava individuals or their size.


The findings emphasise the need to give greater consideration to the traits of plants most likely to invade established communities, particularly forests—namely shade-tolerant, late-successional species. These exotics present a particular management challenge as they often increase in abundance during succession.

The ability of strawberry guava to persist under shade and to attain high basal areas and stem densities can have serious ecological consequences. Strawberry guava has been implicated in studies from numerous tropical regions to alter habitats, modify successional trajectories and impede native plant regeneration. The presence, ubiquity and density of strawberry guava in secondary regrowth rainforests in Australia’s Wet Tropics is therefore a matter of concern.

Alien invasion of the inner space

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