Richard Hursthouse: Let's ban the alien invaders

Our native bush is under serious threat from pest plants and must be protected. The bush provides food and refuge for our wildlife, cleans the air we breathe, filters the water we drink and adds to our sense of identity.

Introduced palms are one of its more recent environmental threats, though the palm varieties have long been popular with gardeners and property developers who do not realise the harm they are doing to native bush.

Palms produce large quantities of berries that are spread into reserves by birds, not choosy about which berries they eat.

As a result phoenix palms are now spreading freely into bush, roadsides and shorelines, threatening to overwhelm native ecosystems.

On one gulf island an entire beach is covered in dense phoenix palms and bush block understory overrun with an impenetrable thicket of toxic spines.

The cost of controlling naturalised phoenix palms is huge, the work hazardous and removing a sizeable tree can cost thousands of dollars. The spines on these palms are toxic and put many into hospital each year with spike injuries and infections.

Phoenix palms (Phoenix canariensis) have now been formally recognised as a pest plant in Auckland, which means they can no longer be legally sold, moved, planted or propagated.

Unfortunately, there are other introduced palm species still widely available and of concern.

The Chinese windmill palm (Trachycarpus fortuneii) is not yet on the pest list and still readily available through garden centres even though it is rapidly spreading into our reserves forming dense under-canopies at several sites around Auckland and it is very common on Waiheke Island.

The bangalow palm (Archontophoenix cunninghamiana) is still for sale and widely spread in the community.

This palm is much faster growing than our native nikau palm. It appeals to those wanting an instant garden and has been a big money spinner for the horticulture industry.

Even the spectacular dragon palm (Dracaena draco) has been found growing naturally in more than one reserve.

The most efficient dispersal mechanism for these palms has been the horticulture/garden centre industry.

Palms are trendy, quick growing and big sellers, which is why the horticulture industry has, up till now, strongly opposed putting any palms on the pest plant list.

But the community has to fund the work needed to remedy the environmental damage caused by sales of these high profit plants.

So what needs to change?

Firstly, gardeners and landscapers need to stop buying, planting and transplanting these palms.

At this stage not all palms are invasive, but if in doubt, plant a native nikau.

The next step is to formally recognise these palms as pest plants and ban their sale. However, a ban will be ineffective unless it is reinforced by a proactive community awareness programme on how best to deal with these plants.

This must then be followed by a systematic removal programme to stop these palms destroying the bush.

Understandably those who love palms, and in particular those who sell palms, may be strongly opposed to these moves.

However our native bush is at serious risk from these rapidly naturalising invaders and the cost of maintaining the bush in a pest-free state is set to soar.

Dr Richard Hursthouse is chair of the North Shore branch of Forest & Bird.