The bold and starkly beautiful environment of the North Island’s Central Plateau with its rare ecosystems has provided the setting for a range of interesting work by Landcare Research in recent years. Plant ecologist Mark Smale has been involved in several projects and knows the landscape intimately. He says he fell in love with the place on his first visit there as a child in 1966, and has never tired of it!. However, working on army land has some interesting health & safety issues. “We had to do an induction course one morning at Waiouru, which included the dangers of examining brightly coloured - or even old rusty - objects lying on the ground all over the place there (potentially unexploded shells).”
Another interesting aspect of working on the Central Plateau is the ever-changing weather. Even in summer, you need to get all rugged up to work in bracing cold winds and rain, then 10 minutes later you need the sun block and sunnies.
Mark Smale of Landcare Research says such dunes rare - one of only a few such ecosystems in the world.
The wild and ever-changing Rangipo Desert is not really a desert because it has ample rain for forest tree growth. There are pockets of forest that may be centuries old but other areas are wind-swept bare of vegetation. This so-called desert area lies between the southeastern flanks of Mt Ruapehu and the Desert Road, covering an area of some 3000 ha. It is mostly administered by the NZ Defence Force as part of the Waiouru Military Training Area. As such, it is a major focus for shelling activities, which presents peculiar difficulties for fieldwork—not only the very limited times available when the area is not being used but also the presence of live ammunition (unexploded shells) in much of it. Intrepid ecologists Mark Smale and his colleagues are up for the challenge, albeit after some serious safety training sessions from the NZ Army.
Mark explains “these sand dunes look much like coastal sand dunes (also created by wind) but occur about as far from the sea as one can get in New Zealand, in the wind funnel between the central volcanoes and the Kaimanawa Mountains to the east. Closer inspection, however, reveals that they lack the predictable linear sequence of crests and swales in fore-dunes and rear-dunes found in coastal systems, instead comprising a chaotic assortment of mounds and hollows in a system being continually created and destroyed by winds from all directions. The sand dunes occur as elevated features in a prevailing matrix of flat gravel, a desolate place reflected in the original Māori name of Onetapu (‘forbidden sands’) that is mostly devoid of plant life and plagued by strong winds and sand and dust storms.
“Virtually nothing is known about our Volcanic Dunes, one of only a handful of such systems in the world. They are under threat from weed invasion and possibly also from military training activities and recreational driving.
“Initially, we planned to sample the vegetation and their associated invertebrates on a sequence of dune mounds of different height — and presumably age — in order to model the changing nature of dune vegetation and some of its associated fauna over time. Mounds proved impossible to define consistently and mound dimensions to measure accurately, so we turned to plant height on dune mounds as a surrogate for mound age.
The annual rings in stem discs (or increment cores from larger stems) provide an indication of the minimum age of mounds and the range of ages revealed so far is up to about 100 years, suggesting a young, dynamic system that is constantly forming and re-forming. However, there are some pockets of forest on the highest dunes that have previously been aged at several centuries that we have yet to sample ourselves. These stands are extraordinary in that they have most of the usual features of rain forest, the unmistakable feeling of a humid forest interior with well-developed ground layers, lower tiers and epiphyte communities, but are in the middle of an otherwise barren landscape that is largely bare gravel.
“Last year we carried out nearly half our sampling and, now that the area is again free of shelling, we are hoping to complete our sampling this summer.“The NZ Defence Force and the Department of Conservation are both keenly interested in knowing more about this unique system and how it can be managed to retain its natural values.
“Previous work in the ‘Army Country’, albeit at much higher elevations, has shown very slow recovery and weed invasion after shelling damage to vegetation and soils, leading the Defence Force to shift shelling operations elsewhere. We hope our work in the Rangipo Desert will indicate how robust - or otherwise - the system is, and whether continued use for military training is an appropriate use for this unique part for the globe.”
Simon Fowler notes beetles continued to spread over the 2009/210 summer, but not as far as predicted (or hoped).
“Last year we predicted the area of beetle-spread would increase to a total area of 36ha (conservative estimate) or 513ha (if beetle breeding really went wild). Despite the beetle population doubling in the past year it has only spread over a further 18 ha to cover 29ha in total. Life on the Central Plateau is not easy, especially if you are a little beetle without much shelter from its extreme weather moods.”
Heather beetles lay 175 eggs each on average in the UK so we expected much more rapid increases in numbers in NZ where they are largely unaffected by predators or parasitoids. In fact, the beetle population has only been roughly doubling for the last 3 years suggesting chronic poor population growth probably due to adverse climatic conditions, low foliar nitrogen levels in NZ heather and issues related with small beetle size as discussed in last year’s article. Exactly how these factors affect the population growth of the beetles e.g. whether low plant nitrogen and small body size reduces beetle egg production, or adverse climatic factors cause major larval or adult mortality, is currently being researched so we can offer mitigating strategies.
These strategies may range from local fertilisation of release sites to promote initially strong beetle population growth to reduce the likelihood of chance events causing the extinction of small beetle populations within a few years of a release, to the option of sourcing larger body size/better climatically adapted beetles from new sites in Europe.
Observations to date support the idea that small populations of heather beetle are vulnerable to chance extinctions. While two new outbreak populations have been confirmed on the Central Plateau this season, five other small populations appear to have gone extinct. Both of the new successful outbreak populations were previously fertilized with nitrogen in 2005 and 2006. To date, we have four fertilized releases that have outperformed paired unfertilized releases, lending support to the fertiliser option.
Despite what looks like a spectacular result at a few established sites, beetle populations still appear to be struggling to survive in most years on the Central Plateau but probably get lucky in some years. Getting lucky may involve getting a nitrogen boost or favourable climatic conditions during critical times during beetle development. If small populations don’t get lucky in the first 3 or 4 years after release, they seem to have a high risk of extinction.
Of the 64 releases made into high altitude Central Plateau sites between 1996 and 2007 only six (9%) have established to date (and three of these were part of an initial nitrogen addition trial). Between 2007 and 2009, a further 28 releases were made in a second, better-replicated, attempt to test the hypothesis that low nitrogen levels in heather foliage on the Central Plateau are limiting population establishment and grow. It is too early for a result from this trial.
Despite ongoing problems with poor establishment and populations growing slower than expected all is not lost. We predict current outbreak populations at high altitude Central Plateau sites probably number 3.5 - 4 million beetles (a 100-fold increase on the number we have released since 1996). Preliminary data from an impact assessement trial suggest that they are doing a good job too.
The Army have historically used herbicide to manage heather. Monitoring for impacts of heather beetle feeding and herbicide application on non-target plant species, and to see if indigenous flora will recover, is also part of this trial.
Contributors to the project include:
Harry Keys and Nick Singers (DOC), John Mangos (New Zealand Army), Richard Mallinson (Environment Bay of Plenty), Peter Wigley (Biodiscovery), Paul Barrett and Jens Jorgensen, Fabiana Preston (Massey University), James Shepherd, Shane Hona, Greg Arnold, Guy Forrester, Quentin Paynter, Shaun Forgie, Merilyn Merrett, Helen Harman and Lindsay Smith (currently or formerly of Landcare Research), Brent Sinclair and Caroline Williams (University of Western Ontario, Canada), Dmitry Musolin (Kyoto University, Japan) and David Renault (Université de Rennes, France). This work was funded by the Department of Conservation, the New Zealand Army and the Foundation for Research, Science and Technology Contract No. C09X0504
In 2009, Simon Fowler and Paul Peterson reported buckets of biocontrol beetles attacking heather, an invasive weed on the Central Plateau of the North Island.
Heather might be nice in the Scottish highlands but on the Central Plateau of the North Island (where silly misguided settlers planted it deliberately), it is a pest plant that’s seriously hard to control. Quite apart from driving over it in tanks and light armoured vehicles, the Army have been using herbicide to manage heather. However herbicides are expensive, produce only short-term results and no-one likes all those chemicals getting in to the environment anyway. In theory, biocontrol is the ideal solution but it is proving a hard battle.
Despite struggling for 13 years to get one of the world’s most promising biocontrol agents working in New Zealand, a watershed point may have finally been reached in 2009. At one site on New Zealand Army land, where 500 heather beetles (Lochmaea suturalis) were released 8 years ago, Simon Fowler and Paul Peterson now estimate that a million beetles (or two 10L bucket loads) have made themselves at home on 11ha of heather (Calluna vulgaris) infested tussock grassland. The beetles are systematically munching their way through the heather leaving, as expected, all other plants untouched.
Since 1996, Simon, Paul and a number of others, have been releasing heather beetles to help the Department of Conservation and New Zealand Army deal with a >50,000 ha infestation of heather on the Central Plateau of the North Island. As the heather beetle is a host specific pest of heather in its native range (where heather is a valued native plant), it was seen as a perfect solution to help deal with our heather problem in New Zealand.
Yet since the beetle’s importation from the United Kingdom in 1996, results have been largely disappointing. After much research Simon and Paul now believe that large fluctuations in spring temperatures at high altitude, low soil nitrogen levels and small beetle size (due to genetic bottle necking) are all probable causes of previous poor establishment and performance. “We still don’t understand the most critical aspects of successful beetle population establishment and growth but relatively mild spring conditions over recent years, releasing beetles at lower altitude sites, and adding nitrogen to release sites have probably contributed to recent successes,” said Paul. Research is ongoing to test the theory that fertilizing with nitrogen at release points can help ‘kick start’ populations through better nutrition allowing beetles to become larger and have more reserves to cope with climatic challenges.
If outbreaks in heather beetle populations continue to grow exponentially, we would expect beetles to disperse over 513 ha next year and 10,000ha the year after that . At this rate beetles could move through the entire heather infestation on the Central Plateau within 3 years. However, a more conservative and realistic model predicts beetles will infest 36 ha next year and 75 ha the year after that (assuming a maximum dispersal distance of 150m each year). But other scenarios are possible too. “Beetles may start to fly on mass as the density increases resulting in smaller outbreaks budding off the main one”, explains Simon.
Paul says that "the best bit of working on the Central Plateau is the relative peace and the awesome feeling of space. It's hard to imagine that some people actually have agoraphobia. "
"The worse bit (which can also be the best bit mind you) is the climate. Temperatures can fluctuate through more than 40°C in just 24hrs. It's probably one of the few places in the country where you could potentially have your sweat freeze. There's a nice mental image for you!"
Contributors to the project include:
Harry Keys and Nick Singers (DOC); John Mangos (New Zealand Army); Richard Mallinson (Environment Bay of Plenty); Peter Wigley (Biodiscovery); Paul Barrett and Jens Jorgensen (Massey University); James Shepherd, Shane Hona, Greg Arnold, Guy Forrester, Quentin Paynter, Shaun Forgie, Merilyn Merrett, Lindsay Smith and Helen Harman (currently or formerly of Landcare Research); Brent Sinclair and Caroline Williams (University of Western Ontario, Canada); Dmitry Musolin (Kyoto University, Japan); and David Renault (Université de Rennes, France). This work was funded by the Department of Conservation, the New Zealand Army and the Foundation for Research, Science and Technology Contract No. C09X0504.
In military exercises in the 1990s, the Singaporean Army shelled parts of the army land on the Central Plateau ... they don’t have room for that sort of thing in Singapore! Mark Smale and his collagues from Landcare Research have been monitoring (that word again) recovery of the explosion craters that were created. The lower-elevation Atawhitiki site is within the zone of unexploded ammunition (lots of brightly coloured objects of ‘uncertain status’ lying about) and after a couple of horses were badly injured and had to be put down after stepping on them, we had to abandon that part of the monitoring exercise. We are still keeping an eye on the higher slopes of the Three Kings Range. However, in the harsh subalpine climate, precious little by way of recovery has happened in the past decade. This has prompted an end to the shelling of this particular area.
The Argo Road runs for miles right into the middle of this vast, empty landscape, and the higher parts provide magnificent views of Mt Ruapehu in the west and brilliant lunch spots. If we are lucky, the friendly occupants of a tank trundling past may stop for a chat.
The Desert Road and the huge block of adjoining Crown land known popularly as “the Army Country” has long been famous for its somewhat controversial wild horses. In the late 1980s, when the horse controversy was beginning, Mark Smale and his colleagues from Landcare Research set up some permanent plots (the bread and butter work of plant ecologists).
On a recent occasion when the plots needed remeasuring, the Army was using the normal quicker route for live firing so alternative travel arrangements were needed. Exquisite autumn weather provided the opportunity for a stunning helicopter ride up the Rangitikei Gorge to the Batley Reserve, where the family kindly allowed us the use of their Lockwood bach while we remeasured cute little Round Bush (so small that the plots take up most of it) and the tussock grassland nearby. Sika deer, seen but mostly heard, were conspicuous in the manuka scrub towards the gorge and seemed to be doing more damage there than the horses.
In 1998, Transit NZ decided to trial the use of the de-icing salt calcium magnesium acetate (CMA) on the Desert Road, one of the highest highways in the country and one with chronic ice problems. (Transit NZ had been chased away from corrosive common salt by vehicle users.) From 1998 till 2008, Landcare Research monitored vegetation and soil changes in the four main plant communities (teatree or manuka/kanuka forest, beech forest, fernland, and tussock grassland) beside the highway to see if they could be related to the use of CMA. Mark Smale says “To date, no significant effects have been observed.”
We have since extended the trial to lower-elevation highways (bordered by conifer-broadleaved forest) that are also beset with winter ice problems, to see if the ‘softer’ vegetation there might be more susceptible to the long-term use of this chemical.
Mark Smale says frost flats are one of the signature ecosystems of the Volcanic Plateau. They were created after vast quantities of pumice were deposited during the titanic eruptions that shaped the plateau. The pumice was washed from the surrounding hills and filled basins and valleys to form plains. These sites are at relatively high elevation (400-800 m a.s.l.) so are focal points for cold-air ponding and they suffer from year-round frosts. The pumice is naturally infertile, and the vegetation is typically dominated by monoao (Dracophyllum subulatum). Fire has also been important in shaping and maintaining the vegetation.
They have been the focus of a 15-year study of succession (changing plant communities). In 1994, DOC alerted us to a fire started by lightening at Rangitaiki, the biggest and best frost flat left, so we rushed down and set up permanent plots to see how the vegetation would change over time. Since then, we have been driving down from Hamilton for a long daytrip (made easier with the advent of Wild Bean coffee at service stations) most years to remeasure our plots, which have now provided us with a treasure trove of data. In the last year or two, the large and cumbersome black-backed gulls have decided to use our plots as a nesting ground, and have killed off most of the silver tussocks that covered half the ground. The gulls are very much a natural part of the system, but what a nuisance for our study!
At various stages during the natural succession of plant communities, the frost flats are home to several threatened and rare plants and insect species. Unfortunately frost flats are vulnerable to invasion by exotic weeds that can cope with low nutrients such as the N-fixers gorse (Ulex europaeus) and Scotch broom (Cytisus scoparius), pasture grasses in nutrient-enriched areas, and other weeds such as heather (Calluna vulgaris). Adjacent agriculture and plantation forestry can result in nutrient pulses that increase vulnerability to weed invasion. Rabbits and hares may be locally abundant. In accessible areas, 4WD vehicles can be especially damaging to the low, scattered vegetation.
Gwen-Aëlle Grelet is using the Tongariro National Park as a natural laboratory where she is investigating the activitiy of mycorrhizal fungi associated with the roots of heather (Calluna vulgaris) and whether this activity is causes carbon to be added or lost from soils.
Plants ‘add’ carbon to soil as litter, but plants also transfer a significant amount of carbon into the soil via their roots. This carbon is in the form of small, labile molecules (such as sugars) that are either leaked out of their roots passively, or actively transferred to the beneficial soil organisms such as mycorrhizal fungi, which are found living in the roots of most land plants.
Mycorrhizal fungi ‘consume’ the bulk of this labile carbon as their main source of energy, and can consume up to one third of all the carbon fixed by plants from atmospheric CO2. Hence these beneficial fungi play a key role as a major carbon sink in most terrestrial ecosystems. However, new evidence suggests that they can also degrade non-labile soil carbon (the carbon locked-up in soil organic matter) i.e., they may behave as decomposers, contributing to soil carbon release.
A major determinant of climate change is the rate at which carbon accumulates in soils: if they switch from a being a net sink for carbon to a source of carbon (CO2) climate warming will increase. Future soil carbon balance will depend on whether the organic carbon released from soil by decomposer organisms exceeds that contributed to soils by plants.
The mycorrhizal fungi forms symbioses with the roots of ericaceous plants ,such as heather, are called ericoid mycorrhizal (ERM) fungi. This type has the greatest decomposing abilities of all mycorrhizal types, and due to its prevelence in C-rich soils world-wide, it may have the greatest impact on soil C at the global scale.
Part of Gwen’s research is determining how invasive ERM plants and fungi are threatening the native ecosystem and many plant species endemic to New Zealand.
The other aspect of her work is determining what happens to soil carbon when the ERM fungi hosted in the roots of heather can (or cannot) access plant labile carbon. This will require the development of two state-of-the-art stable isotope techniques for tracing carbon use by individual species and carbon release from soils; these techniques will have multiple applications in environmental and agricultural studies.
The project is geared to provide essential information for the management and conservation of biodiversity in Tongariro National Park, and key strategic information for the understanding of soil carbon sinks under future climate, which may result in modification of current soil carbon models.