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Red cabbage palm

Using current definitions, the red cabbage palm in Central Australia can be classified as native or non-native (Source: Genelle Weule)

Earlier this year, a news story about how Aboriginals could have moved the iconic red cabbage palm to Central Australia between 15,000-30,000 years ago focused our sights on an important issue: how do we decide which plants and animals are native?

What we found were outdated, conflicting and even racist definitions that aren't equipped to deal with how plants and animals move around, particularly in a world with a rapidly changing climate.

Using current definitions, the red cabbage palm in Central Australia can be classified as native or non-native depending on which definition you choose. The problem is, individual populations can't be native and non-native at the same time.

The conflict between definitions suggests it's high time we had a single relevant definition to use.

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Dispersal method and time

Most species are native somewhere, so it is plant and animal populations (not species) that get the native or non-native tag. There are a range of definitions currently used by policy and management to decide if populations are native or not.

It is critically important to know whether a plant or animal population is native. A non-native tag 'raises the red flag' to biosecurity, pest and weed managers that the population may have negative impacts. The tag is used as a tool to help make decisions about whether we conserve or control particular populations.

Native status is currently assessed on the basis of two ideas: dispersal method and time. The problem is these concepts are challenged by our increasing knowledge on how commonly humans have moved species throughout history, and the continued deliberate movement of rare and threatened species for conservation ('managed relocations').

Dispersal is the way that a plant or animal arrived in a new area. With current definitions, new populations established with human help (either deliberate or accidental) are non-native. Superficially this might appear an effective way to decide if a plant or animal is native. However, 'managed relocations' are usually treated as native, even when they are deliberately moved well beyond where the species is currently known from.

'Managed relocations' may seem a great adaptation response to conserve species with climate change and certainly is done with the best of intentions. But do these new populations deserve the native tag? What if they were to have negative impacts in their new region? Is it appropriate to give all these new populations the same tag, when they might be established a few tens of metres or perhaps thousands of kilometres from the original population?

Time relates to the idea that if a plant or animal was present in an area before an arbitrarily agreed date, then we're going to give it the native tag. This definition seems attractive for its simplicity, but the arbitrary date chosen has no scientific basis and doesn't tell us anything about the history of the species.

The red cabbage palm is one example of how new scientific insight is showing us that humans have moved species around over many millennia.

If we use international definitions, the red cabbage palm is classed as non-native, because of the likely human involvement. Using Commonwealth or Northern Territory definitions, it's native. Commonwealth legislation applies an arbitrary date of 1400 AD, while the Northern Territory legislation uses 1788 AD.

The Northern Territory definition has an extra level of complexity, because it only invokes a date if Aboriginal people moved the species. Were the early European explorers or the Makassan traders who visited Australia well before 1788 any less able to disperse plants and animals?

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A new definition

A recently proposed definition for deciding if something is native, is based around the concept of a 'projected dispersal envelope'.

This definition uses ecological theory to work out if a population could have moved naturally to where it is (in the time available), not how or when it moved there.

The new definition uses scientific methods to assign native or non-native status to populations of plants and animals establishing in new areas, including as a result of a changing climate. Because the new definition can be applied universally, it would mean the end of conflict between different definitions.

Plants and animals establishing naturally in new areas would have native status. New 'managed relocation' populations would have native status if they could have got to the new location naturally.

This new approach brings consistency and transparency to defining natives and non-natives. This allows us to apply a broad range of scientific insight to best determine which tag should be applied. Current definitions are outdated, inconsistent and becoming increasingly unworkable in a world experiencing rapid climate change.

While we're updating how we define native and non-native, we should take a good long look at how we choose to manage these populations. The current mantra of: "Conserve natives! Control non-natives!" holds sway in both management and policy. We emphasise the need to look beyond these tags when deciding whether to control or conserve, particularly in an era of rapid climate change.

We propose that a range of other criteria should also be considered, including how the population contributes to ecosystem function and stability, and cultural heritage values associated with the population. The red cabbage palm scores well under all of these criteria, and we advocate its conservation even though it has a non-native tag.

We recognise that a change to embracing new definitions for native and non-native may be challenging, and that many criteria used to determine management directions will be value-laden and controversial. But it is clear that existing definitions are inadequate, and we have to start the discussion sometime. Why not now?

About the authors:Ms Melinda Trudgen is a plant scientist with experience in taxonomy, vegetation distribution and environmental impact assessments. She is currently a PhD candidate with the University of Western Australia and CSIRO Ecosystem Sciences, and her research focus is on how non-native street trees can become invasive weeds.

Dr Bruce Webber is a plant ecophysiologist working with CSIRO Ecosystem Sciences, and the University of Western Australia. His current research explores the effect of rapid global change on plant-resource allocation and plant-ecosystem interactions, such as the effect of climate change on invasive plants and future food security.

Tags: environment, environmental-management, animals, botany

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Published 05 September 2012