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Invasive Alien Species

Invasive Alien Species (IAS) is known as one of the main threats leading to biodiversity loss. Addressing concerns caused by IAS is crucial because the threat is ever increasing and the impacts on our environment can be severe, if not managed. The most cost effective way to deal with the impacts of invasive species is to prevent invasions before they even occur. Not many are aware of the impacts invasive alien species can have on our local biodiversity and environment. This is a good opportunity to share knowledge on non-native species and engage the community in helping to prevent the spread of invasive alien species in our ecosystem.


Outline of contents

What is an Invasive Alien Species?

‘Alien species’ refers to plants, animals and microorganisms that are exotic, non-native, introduced or non-indigenous, with respect to a particular ecosystem. They become invasive when accidentally or deliberately introduced to new areas beyond their native ranges, and are able to survive, reproduce, and then spread and cause a negative impact on local biodiversity (Tu, 2009). Generally, the spread of an IAS involves four stages: Introduction, Establishment, Invasion and Spread.

Why are they a problem?

Invasive Alien Species can cause negative impacts at the species, population and community levels, and the most significant harm is altering ecosystem functions. Invasive alien species can potentially caused a range of problems such as the following:

  • Threaten the survival of native plants and animals by competing for resources - Alter vegetation structures and community composition, thus upsetting the ecosystems balance - Spread easily if not managed properly
  • Costly to control if not managed properly
  • Endanger human health if organisms harbour foreign pests and diseases
  • Hydridise with native species, resulting in negative genetic impacts

How are they introduced?

Alien species can be introduced via 2 means: a) Unintentional & b) Intentional.

An unintentional introduction occurs as a result of accidental or unplanned means, utilising humans or human delivery systems as vectors for dispersal outside its natural range.

An intentional introduction is a deliberate introduction of an alien species by humans, involving the purposeful movement of a species outside of its natural range and dispersal potential.

(Ref: IUCN Guidelines for the Prevention of Biodiversity Loss caused by Alien Invasive Species, 2000)

Examples of unintentional introduction

  • Ballast water releases from ships, hull fouling
  • Organisms in or on timber/wood products, in packing materials and shipping containers/cargos
  • In or on various modes of transportation like cars, trucks, boats, airplanes, ships, etc
  • Organisms in imported nursery soils
  • Organisms in imported fruits and vegetables
  • Tourists and their luggage/equipment

Examples of intentional introduction

  • Release of unwanted pets and aquarium animals into the wild (e.g. Red-eared Slider)
  • Plants introduced for gardens/landscaping
  • Biological control (e.g. House Crow)

Apart from preventing the introduction of alien species, one of the actions taken to prevent the spread of invasions is to identify the pathways through which invasive alien species arrive.

Managing non-native: How is Singapore dealing with the issue?

Laws and Regulations

The use of legislation is an important component in the management of alien species. A set of legislation administered by different government agencies are used to facilitate the management and preventing the spread of non-native in Singapore. Listed here are the relevant Acts under administration by the respective agencies




Animals and Birds Act

Regulates the import, export and transshipment of animals


Wildlife Act

Regulates the feeding, release, killing, trapping, taking, keeping, sale, import, and export of wildlife


Control of Plants Act

Regulates import and export of plants and plant products


Endangered Species (Import and Export) Act

Regulates trade in endangered species of plants and plant products


Parks and Trees Act

Regulates the planting, maintenance and conservation of trees and plants within national parks, nature reserves, tree conservation areas, heritage road, green buffers and other specified areas. The Act also specifies that release of animal is prohibited in the nature reserve.


Prevention of pollution of the sea Act

Regulates the prevention of sea pollution, whether originating from land or from ships (with reference to ballast water).


Conservation Management

NParks actively clears exotic plant species from Singapore’s forests. Over the years, exotic plants, mostly climbers and creepers, have been thriving along the rainforest edges and are a threat to the native plant species. These creepers strangle trees, and often cause their collapse during heavy thunderstorms because of the intertwining creepers that connect several trees together. In addition, the creepers also compete with saplings of native plants for space. Hence, there is an urgent need to manage these exotic species before they penetrate further into the rainforest.

In 1997, a project was undertaken by NParks to remove exotic species along a 3km stretch of rainforest, at the edge of the Central Catchment Nature Reserve (CCNR). Most of the trees were badly covered by climbers and creepers, including exotic species such as mile-a-minute (Mikania micrantha).

Once an area has been cleared of exotic species, it is earmarked for reforestation. Together with the help of students and volunteer groups, NParks carries out reforestation activities and ensures that only native plants are replanted.

Schools and other public and private organisations also contribute towards the maintenance and management of the nature reserves by adopting patches of land. This serves as an opportunity for students and the general public to learn about ecology and the experience of managing an ecosystem. Students also take this opportunity to carry out simple research on reforestation techniques.

Click here to read an article on the management of an invasive plant species, Dioscorea sansibarensis, at the Singapore Botanic Gardens.


One of the ways to minimise the release of non-native is through public education. Members of the public can increase their knowledge on the potential impacts of non-native species on our local biological diversity and ecosystems by obtaining information through talks, brochures, internet and books. Do your part by sharing what you know on invasive alien species with your family, friends and neighbours. Spread the word around so that more people can understand the damage caused by invasive alien species.

“Operation No Release” is a programme targeted at discouraging the “mercy” release of animals or unwanted pets into parks and nature reserves. This programme came about in response to the problem of members of the public releasing animals (often into the CCNR) to gain merit, especially during the annual Vesak Day. Though releasing of animals on Vesak Day is a well-intentioned act of kindness, those who practise this fail to realise that they are doing more harm to the animals as well as upsetting the ecological balance. It is especially detrimental to our local ecosystem when the release involves alien species that can negatively affect local biodiversity. One of the popular animals released is the red-eared slider, which can be easily bought from the local aquarium shops or markets.

In order to heighten awareness on the problems associated with releasing animals, NParks together with AVA, PUB, Nature Society (Singapore), students from various schools and volunteer groups conduct educational and outreach activities. These activities include talks, exhibitions and producing/distributing brochures, are often carried out before Vesak Day. On Vesak Day itself, NParks rangers and volunteers station themselves at popular release sites around the CCNR to discourage members of the public from releasing animals. The Public Utilities Board (PUB) also plays an important role here by educating the public on the detrimental effects on our water quality if the released animals are released into the reservoirs.

Since the initiation of this programme, there has been a noticeable decrease in the number of animal releases. Alternative ways of performing good deeds have been suggested such as planting suitable native trees. The general public are also now becoming better informed of the consequences of animal release into our nature reserves and reservoirs.

What you can do to help?

Prevention is better than cure! The best way to stop alien species from spreading is to stop them from arriving and establishing themselves in a new ecosystem. All of us can do our part to help stop and prevent the introduction and spread of these harmful invaders by following these helpful tips:

Here are some tips on controlling spread of alien species for gardening, pets and during travel.


  • Avoid buying or growing plants that are known to be invasive such as Ceropia. Replace any invasive plants in your garden with non-invasive plants which are native.
  • Use native plants to landscape your garden. Although non-native plants are not necessarily invasive, and can usually be grown without risk, growing natives can provide bonuses such as food, cover, nesting sites for birds and butterflies.
  • Avoid planting of exotic garden shrubs but if you do so, avoid planting them next to, or within nature reserves and natural areas.
  • Learn which plants are invasive and remove them from your garden. 
  • Avoid dumping unwanted plants in a nearby park or natural area. Invasive plants can spread very easily from plant fragments, seeds and berries.


  • Buy from reputable pet dealers whose non-native pets have proper labels, legally imported and not harbouring foreign pests and diseases that can spread to native wildlife.
  • Avoid releasing aquarium fish into natural water bodies, such as ponds, reservoirs, or natural streams. Some ornamental fish can establish themselves in the wild with deleterious effects on native biodiversity. If you do not want your pet fish, return it to a local pet shop for resale or give it to another hobbyist, or donate it to a school. Be a responsible pet owner.
  • Avoid releasing other pets, either. Some pet amphibians and reptiles may prey on a wide variety of native species and others may carry diseases. Most domesticated pets such as rabbits and hamsters are not able to survive if release into the wild and may carry diseases, which may have an impact on local biodiversity.


  • Avoid carrying seeds, live plants, fruit, vegetables, soil, insects, lizards, snails, or other animals into or out of the country. Travelling with these biological items can add to the spread of exotic species from one ecosystem to another.
  • Abide by local and international quarantines to prevent the spread of serious insect pests, weeds and diseases.


  • Share the knowledge about the potential damage caused by invasives with your friends, family, neighbours and colleagues at work.
  • Learn to recognise common invasives and keep a look out for signs of new ones. The best way to tackle a potential invasive problem is early detection and stopping them from becoming permanently established.


Note: The list above was collated from sources such as Invasive Alien Species: A threat to biodiversity produced by CBD.



Want to learn more about IAS?

Here is a list of materials and websites pertaining to IAS if you want to find out more.

Web Resources

Convention on Biological Diversity – Invasive Alien Species

GloBallast Partnership

Global Invasive Species Database

International Day for Biological Diversity 2009 – Invasive Alien Species

The World Conservation Union (IUCN) - Invasive Species Specialist Group


Brook, B.W., Sodhi, N.S., Soh, M.C.K. & Lim, H.C. (2003) Abundance and projected control of invasive house crows in Singapore. Journal of Wildlife Management 67(4):808-817.

Lowe S., Browne M., Boudjelas S. & De Poorter M. (2000) 100 of the world’s (Ahyong & Yeo, 2007)Database. World Conservation Union, Invasive Species Specialist Group (ISSG).

National Parks Board. (2000). Thematic report on alien and invasive species. Accessed on May, 1, 2009 from

Secretariat of the Convention on Biological Diversity (2009) Invasive Alien Species : A threat to biodiversity. Accessed on May, 1, 2009 from

Sodhi, N.S. & Sharp, I. (2006) Winged invaders: ‘Pest’ birds of Asia-Pacific. Singapore: SNP. 

Teo, D.H.L., Tan, H.T.W., Corlett, R.T., Wong, C.M. & Lum, S.K.Y. (2003) Continental rain forest fragments in Singapore resist invasion by exotic plants. Journal of Biogeography 30:305-310. Accessed on May, 1, 2009 from

Tu, M. (2009). Assessing and managing invasive species within protected areas. In J. Ervin (Ed.), Protected Area Quick Guide Series. Arlington, VA: The Nature Conservancy. Accessed on May, 1, 2009 from

List of alien species in Singapore (PDF, 150KB)

Last updated on 14 April 2022

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