In the central plateau of the North Island of New Zealand, the climate is mild and wet. The pumice soils of the Tongariro Volcanic Centre are thin and poor, so that much of the area is covered with low tussocks of native plants.

In 1910, the wardens planted European heather to provide a habitat for grouse, a game bird introduced from Scotland. The grouse died out, but the heather spread at an amazing rate, and has rapidly become an out-of-control pest plant. It now infests 50,000 ha¹ of the North Island's Central Plateau. Since it damages the habitat of native plants, heather is considered a noxious weed in the North Island. It is now being slowly taken back into line by the heather beetle, which is a biological control. The heather took over an area of ground that is above the tree line in the tongariro area, and is wiping out the native plants, such as the red and golden tussocks.

What Is Heather?

Heather is a plant that is foreign to New Zealand. The type that has infested New Zealand is native to Scotland. It has grown out of control and is destroying the native plants, such as the red tussock, in the Tongariro Volcanic Centre. Its scientific name is Calluna Vulgaris, and it comes from the family of Ericaceae. This huge family includes many of the most well known and rewarding of flowering shrubs. Like Calluna Vulgaris, most prefer moist, acidic conditions. The many types of Calluna Vulgariscan be differentiated by the flowers, though the foliage can also vary. It is sometimes known as the Red Heath, Scotch Heather or Ling and can be confused with the heaths Erica, and the bell heathers Daboecia.

It grows on poor, undeveloped grasslands with acidic soils and prefers frost flats, scrub and higher tussock grasslands up to a height of 1500m above sea level, where the winters are cold. It also tolerates waterlogging, and can be found in wet bog communities.

The shape of the bush depends on the environment, varying from low-lying mat-like forms to upright ball-shaped bushes and dwarf trees.

Reaching heights of 50-125cm, heather is an evergreen perennial shrub. The small oblong leaves are initially dark green, later turning brown and grow in four rows along the length of the branches. The flowers, which are bell-shaped and very small vary from white, through pink to purple, pale purple being the most common.

It likes more sandy soil, and the soil in the Tongariro Volcanic Centre area is ashy, which suits the heather very well, as ash is quite sandy.

Flowers start to develop during autumn, and buds open during mid to late winter. As the fruit ripens and the seeds develop, the petals turn brown and dry out and the flower moves from hanging downwards (pendant) to an upright position. It reproduces mainly by seeds. Each plant can make a few thousand flowers, and literally tens of thousands of seeds, with seed production reaching one million seeds per square metre. The seeds themselves can remain viable for extended periods, even up to 100 years, and are spread by wind, animals or walkers brushing against the plants. The seeds rarely germinate without exposure to light, and the germination rate increases when the seeds are heat-treated. Branches in contact with wet soil can also produce roots and form a new plant, a reproductive process known as 'layering'. It does not tolerate shade, and exhibits lower shoot production and reduced flowering in shaded conditions.

How Does Heather Affect the Native Flora and Fauna?

Although the seedlings of the heather are small and easily out-competed by grasses, as a mature plant it forms a dense canopy which can reduce species diversity in sensitive upland habitats, such as the Tongariro Volcanic Centre. With this canopy, and the constant leaf litter it produces, the mature heather plant virtually wipes out any other plant around it. This ability to so easily dominate other plants always leads to a severe loss of biodiversity by displacement of native vegetation and reduction in the range of habitat available to native fauna. As has been stated before, each heather plant produces tens of thousands of seeds, and even if only 0.1 of a percent of those seeds grow, that's still ten plants per parent plant per year; which might not sound like much until you realise how many of these plants there are already in the area affected. Also, bush fire, deadly to the native plants, just helps the heather to grow more, as it requires high temperatures for seed germination.

As it spreads at such a rapid rate, and because at the beginning it was encouraged as a habitat for the grouse, the heather has taken over a large area of land, displacing the native species of flora which would normally have been growing in that area. The native fauna is also at risk, as the herbivores cannot live off the heather and die out; the native carnivores are in turn deprived of their food source and die out as well.

An example of the native plants affected are the red and golden tussocks, and the bidibid, or piripiri, which has medicinal purposes, and can be used in uber-tea. As you can well understand, the heather has created a vicious circle, one that unless stopped soon will result in the destruction of the fragile ecosystem that is the Tongariro Volcanic Centre.

Calluna Vulgaris has been recorded as a weed not only in New Zealand, but in many other countries as well, such as Australia where it threatens the ecosystems in Tasmania, Victoria, New South Wales and Australian Capital Territory. Even though heather is a weed, some shops still sell it. These plants can spread around by seed distribution and inappropriate dumping. If heather is found for sale, the proper authorities, namely the Department Of Conservation, should be notified immediately.

The Heather Beetle

The Heather Beetle is a beetle which preys on the heather plant. The scientific name of the heather beetle is Lochmaea Suturalis. It is native to northwest Europe, and was first imported from the UK into New Zealand by Landcare Research in 1992. The New Zealand Government chose it, as well as some other options, as a biological control which means they control the heather problem to an extent. The heather beetle is the primary biological control, because it is a long-term solution that does what it is supposed to, and is not harmful to the New Zealand ecosystem either now or in the future.

The other control methods can only be secondary because they are either impractical to perform on a large scale, or are quite harmful to the ecosystem. These controls are: spraying the heather with herbicides regularly to completely kill the heather off; and removal by hand. Herbicides need to be reapplied quite often to the heather plants, because they are partially resistant to it, and pulling the plants out only works as a short-term method because the root systems can recouperate and grow back new heather plants. Fire is not used as a control, as heather copes with fire better than the native species. The heather is close to the motorway, and so is readily at hand for the DOC officials to work on.

The adult beetle is brownish in colour, and about six millimetres long. You are unlikely to see any on the heather plant, because of the beetles' cryptic behaviour and their tendency to drop to the ground when disturbed unless present in large numbers. Adults spend the winter in moss or litter at the base of plants, until rising temperatures in spring stimulate them to emerge, feed, and produce their eggs. These beetles are capable of flying at least three kilometres after this spring emergence, but will only do so when the heather around them is in a poor condition. They do not respond well to extreme conditions, such as an unprecedented coldness level in the winter, but are generally regarded as being the best option there was, albeit a long-term option. Those released in New Zealand were free of European parasitoids and predators, as a result of careful rearing and breeding through one or more generations in quarantine before release.

The release of the heather beetle into the environment was the best and easiest solution to the heather problem, so was the obvious choice for dealing with the problem of the heather. It is hoped that the beetle will put ecological restraints on the plants, even if it doesn't completely kill the heather off. If the heather beetle continues to multiply and spread, it is hoped it will become an effective tool for helping the Department of Conservation, the New Zealand Army, and the regional counsels affected to control the threat of the heather. In fact, only two years after their release, there was major damage to the heather in the area around the release site.

The heather beetle was released in six separate areas around the area affected by heather but only one of the groups survived, the group established at Te Piripiri which has done well despite a reduction in numbers a few years after release. It is believed that the poor establishment and success of the heather beetle was mainly due to adverse weather conditions around the Tongariro environs. Unseasonably cold conditions in the Tongariro Volcanic Centre in the spring of 2002, including the lowest minimum temperature in October for at least 18 years, and unseasonably late snow falls, could have been the cause of the reduction in the beetles' numbers at Te Piripiri.

How the Heather Beetle Affects the Heather

The beetles are herbivores which survive on a diet of only heather. They do not eat the entire plant; they just damage it enough so that it dies by transpiration, which is when the plants suck up the moisture from the soil. The heather dies because it is losing more water than it can produce in the time, and so dehydrates quite quickly, which leads to the heather plant's demise.

The heather beetle is astoundingly effective, especially in numbers, when you consider its size. It is amazing to think that since 1992 the heather beetle has had such a large effect in the areas in which it has been working, as it has done. Due to a small population size, the effect is only noticeable in one area, but that area is completely free of Calluna Vulgaris in any way, shape or form. The native plants are beginning to repopulate the areas that have been cleared by the heather beetle, and it is clear that if more resources were put into the heather beetle project, the whole heather project could be out of the way in another twenty to thirty years (taken from the Department of Conservation website).

If you go for a walk through the area in Te Piripiri where the beetles are, you can see positive identification of their passage. Not only is that area bereft of the noxious weed, but the heather plants around the drop point show positive signs of being eaten by the small beetles: ie, bitemarks through the leaves of the heather plants, and some of the heather plants standing dead and desolated in the control area.

Why the Heather Beetle Doesn't Eat the Native Plants

The heather beetle, or Lochmaea Suturalis, was thoroughly tested to see if it would eat the native plants. The result was that, although there was one plant that the heather beetle could survive on - P. pumila, a type of native pine - it preferred heather to this, and so would not pose a threat to native plants. The beetles would rather die than eat the other native plants, as was shown in the tests. The heather beetle then is no danger to native plants and the ecosystem of the Tongariro Volcanic Centre, and so was the best choice for the job at hand: ie, the extermination of the heather problem.

Dr Simon Fowler, from Landcare Research said, In the existing small outbreak site, we can confirm that despite the severe damage to heather, no native plant species appear to been attacked at all. As luck would have it, the one native species that was nibbled by heather beetle during testing (P. pumila) is present under dead and dying heather at Te Piripiri: gratifyingly, it looks perfectly healthy despite the thousands of heather beetle larvae and adults finishing off the heather! Other native plants such as Dracophyllum spp (also on the test plant list) are very visible as 'islands' of undamaged foliage in the patch of dead and dying heather. These observations provide confirmation of the accuracy of predictions about the host range of the beetle from pre-release testing.

Dr Harry Keys, from the Department of Conservation, is one of the main people working on the heather beetle project, and he concurred with Simon Fowler in this explanation, except that he added that prior to the beetles release, there were a number of lab tests that told them that the heather beetle couldn't live off most of the native plants, and did not live long if it ate a diet of the few others, and if given a choice between heather and a native, went for heather every time. The heather is also restricted by natural barriers such as rivers.

The information that these renowned doctors have supplied is very helpful, as it tells us for certain that the native plants are in no danger from being munched by hungry heather beetles while there is heather around to munch. This is very important, because it means that the heather beetle will clear up the mess while causing no extra harm to the already damaged native ecosystem.

Conclusion

In conclusion, Calluna Vulgaris is an invader in New Zealand - a plant that is considered a noxious weed in that country, although it is thought of very differently in its native Scotland. Areas where it flourishes can be assigned the status of Site Of Special Scientific Interest. It out-competes the native plants of New Zealand by crowding and overshadowing. It needs to be driven out of the ecosystem, and the best way to do it is with the heather beetle. The beetle is the best hope for the resuscitation of the native flora and fauna of the Tongariro Volcanic Centre.