A Closer Look / At the Beach Casuarina

ANDRE LEU

The Beach Casuarina or Beach She-oak (Casuarina equisetifolia) is a graceful species with fine long pine-like needles that commonly grows along our beaches of northern Australia. It is a widespread Indo-Pacific species found from Madagascar, Bangladesh, Myanmar, Thailand, Malaysia, Cambodia, Vietnam, southern China, Taiwan, southern Japan, Philippines, Indonesia, PNG and the tropical Pacific Islands. One subspecies grows as far south as northern NSW.

It was officially described by Linnaeus, the founder of modern taxonomy, in 1759, based on specimens sent to him from Indonesia. The name for the genus (Casuarina) comes from the Indonesian word for the Cassowary, Kasuari, (our word ‘Cassowary’ comes from the same Indonesian word) because he thought the bird’s feathers were similar to the plant’s foliage. The specific name (equisetifolia) comes from the Latin words for ‘horse’ and ‘foliage’ because the way the fine long needle-like leaves hang down from the branches reminded him of the hairs of a horse’s mane or tail.

Casuarina is an Indo-Pacific genus with 17 tree species. Several are widespread over the region while others are restricted to distinct geographic regions such as Australia, eastern Africa, the Indian subcontinent, southeast Asia, and tropical Pacific Islands.

Casuarina equisetifolia is the most widespread of all the Casuarina species. It is commonly found on tropical coasts growing together with the other main Indo-Pacific coastal species such as Mastwood (Callopyllum inophyllum), Beach Almond (Terminalia cattapa), Beach Hibiscus (Hibiscus tiliaceus), Cardwell Cabbage (Scaevola taccada), Coconut (Cocos nucifera) and the Banyan (Ficus microcarpa).

The leaf litter from its pine-like needles puts out a poison that suppresses the germination of understory plants through a process known as allelopathy. Large numbers of closely growing trees will severely suppress and even kill many understory plants. Casuarinas fix their own nitrogen in symbiosis with a micro-organism called Frankia. This gives them the ability to rapidly colonise nutrient-poor soils such as beach sand or degraded cleared areas. It is an important pioneering species in the tropical Indo-Pacific region.

However, because it can rapidly colonise areas and suppress the understory plants, it is regarded as a seriously damaging invasive species outside its native range, and it has been banned in many countries. Because it damages the coastal understory leaving bare ground, it is regarded a major cause of beach erosion in Florida and the Caribbean, where it is called the Australian Pine.

However when mixed with the native species that commonly grow with it, rather than growing in single species stands, it doesn’t dominate, and becomes the iconic and elegant species that graces our northern Queensland beaches.