Threats and the decline of Pohutukawa and Rata

The pohutukawa and rata forests which once turned coastlines and hillsides red are unlikely to be seen again. The reasons for this are many.

  • The Australian brushtail possum tops the list (read more below). Possums eat the leaves, buds, flowers and young shoots of the trees and can kill a mature rata within two years. In some areas they have contributed to the dieback of extensive areas of rata.
  • The tiny seeds of pohutukawa and rata do not have enough food reserves to last long in soil, nor the strength to push a young sapling through the matted roots of grass, kikuyu and other weeds that invade areas where the trees might grow.
  • The tree’s roots, designed for spreading over the rocks, are also easily damaged, whether by farmers leaving trees unfenced in stock grazing paddocks or by people tamping over, or driving and parking on the roots.
  • In New Zealand’s early history rata numbers declined alarmingly as potential rata hosts were felled for timber, and forests cleared for farm buildings and stock.
  • The historical use of fire in land clearing was fatal to pohutukawa which are extremely sensitive even to low intensity fires – a light grass fire at its base can kill a mature pohutukawa.
  • People today are still removing trees to clear space for new buildings, improve views or during general landscaping alterations.
  • Hybridisation between the two species threatens the survival of each individual species. For this reason Project Crimson strongly adheres to the rules of ecological sourcing of seed and trees.

Myrtle Rust

Myrtle rust (Puccinia psidii), a disease which affects plants in the family Myrtaceae, is recorded from over 440 species worldwide. Found established in Australia in 2010, and present in Hawaii, Japan, and southern China, there is concern that it will eventually reach New Zealand and cause damage to native Myrtaceae including pohutukawa, rata, kanuka, and manuka.

The disease damages foliage and shoots and in some cases flowers and fruit and on some species causes tip dieback but rarely kills mature plants. While its likely impact on New Zealand Myrtaceae is unknown, there is concern that it could affect regeneration.

The disease appears as a powdery bright yellow or orange/yellow pustules on actively growing leaves, shoots, flower buds and fruits of infected plants. Leaves may become buckled or twisted and die off.

This fungus is NOT present in New Zealand. If you suspect the presence of myrtle rust on plants in New Zealand, call MPI’s Exotic Pests and Diseases hotline on 0800 80 99 66. Read more on this Fact Sheet from the Ministry of Primary Industry.

Do not attempt to touch or collect samples as this may increase the spread of this disease.  You can read more about this on the Ministry of Primary Industry’s website here. 

Possums

The Australian brush tailed possum was introduced into New Zealand in 1837 to establish a fur trade. Inits native land the possum is up against dingoes, bush fires and less palatable vegetation, but in New Zealand conditions are so favourable it often breeds twice in one year.

It was estimated that the New Zealand possum population topped 70 million during the 1980’s and 90’s. Landcare Research now estimates that figure around 30 million, but the number has not been confirmed as the cost to do so would be better spent reducing possum numbers even further.

These so-called cute furry marsupials ravage the bush — it has been estimated they chew up seven million tonnes of vegetation a year.

possumproblem

Why are Possums a problem?

The damage to native forests can be seen all too clearly in many areas. Possums ignore old leaves and select the best new growth. In some areas they have eaten whole canopies of rata, totara, titoki, kowhai and kohekohe.

Possums compete with native birds for habitat and for food such as insects and berries. They also disturb nesting birds, eat their eggs and chicks and may impact on native land snails.

Dairy and deer farmers have the added worry of possums spreading bovine tuberculosis. Possums are also a nuisance in suburban gardens, and sometimes even indoors.

Methods of Control

Prevention

Deprive possums of nesting sites on your property by blocking off sheds and barns.

Physical barriers around areas of bush and on individual trees (such as placing metal strips around the trunks) offer some protection but are often unsightly and bypassed by smart possums.

You can protect trees with repellents such as the commercially-available Thiroprotect, or homemade mixtures such as:

  • 10 parts melted fat to one part kerosene. Allow to set, then spread on the base of the tree.
  • 5 fresh eggs, 600 ml water, 150 ml acrylic paint. Stir well and apply 20 ml per tree after planting.

1080 and Cyanide

To handle or purchase 1080 or cyanide you need to be licensed by the Environmental Protection Authority(at a fee), and have the written approval of the landowner where you intend using the poison.

EPA will supply further details on the regulations covering this poison and the licence requirements, find out more here.

In some places aerial 1080 operations are the only effective way to control possums. In rugged, inaccessible areas where ground baiting is too difficult, local regional councils in conjunction with DOC undertake carefully controlled aerial drops of 1080. This means about one teaspoon of 1080 per hectare is applied.

1080 is an essential pest control tool. Severe possum damage to the pohutukawa forests on Rangitoto Island led to a dramatic decline in honey production in the 1980s. In the 1990s possums and wallabies were eradicated using 1080. New shoots on the pohutukawa tree trunks began appearing within weeks of the drop. However honey production only bounced back 10 years later when the trees fully recovered.

Likewise rata and fuschia are flourishing on the Otira valley in Arthur’s pass after 50 years of 1080 drops. Ten kilometres down the road on the Arahura valley where there’s no pest control, rata skeletons are abundant, and the forest is silent.

Watch a clip from the Department of Conservation about the use of 1080 here.

You can find out more information about the use of 1080 for possum control on the below websites:

Alternatively, cyanide causes near-instant death of possums and allows easier recovery and monitoring of any operation. Cyanide is a highly volatile and toxic poison, which needs to be used with care. It is available either in tubes and is mixed with feed paste, or in encapsulated form as Feratox. However, unlike 1080 cyanide has killed kiwi and can kill people. 1080 hasn’t killed kiwi and no deaths have been recorded for humans.

Bait Stations

Bait stations are widely used by possum control agencies to give sustained control of possum populations, with minimal risk to humans, pets or livestock. A wide range of baits and bait stations are now available.

Baits available for the home user include those that are cholecalciferol or brodifacoum based. No licence is required, but follow the manufacturer’s instructions and be aware of the first aid steps if the poison is accidentally eaten by humans or domestic animals.

A range of bait stations are also available. Most are made from plastic and are sealed at the top but open at the bottom for feeding. Protection from the weather increases the effective life of the poison. Bait stations should be fixed above ground, such as in a tree, where the possums can easily reach the bait. They need to be placed high enough to be clear of children, pets, livestock and ground-feeding birds, such as weka.

Each bait station will cover a range of 100 metres. Site the station where the possum is looking for food or on identifiable possum runs.

Timms Traps

The Timms kill trap is a humane pest trap designed for controlling possums. This trap is a strong bright yellow plastic `box’ which in itself acts as a lure. The possum puts its head into a keyhole opening, attracted by a bait such as apple, kiwifruit or orange. Fruit baits make it unlikely that animals such as cats will be caught. When the possum investigates the bait a trigger is released which brings a striker rod up under the possum’s neck.

If the bait is too large or too small it won’t set off the trigger. An ideal size is 25mm in diameter.

Set Timms traps close to dry nest sites, around trees known to be possum favourites, indoors in the rafters or nailed to fenceposts or trees. Take care to set them out of reach of pets, children and ground-feeding birds, such as weka. Timms traps are widely available and come with a comprehensive leaflet of instructions.

You can find a list of product suppliers for bait and traps on the National Pest Control Agencies website here.