Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Protecting Biodiversity and Landscape Values on the Desert Road

Broom threatening the Central Plateau.

Broom threatening the Central Plateau.

Anyone with a keen eye for spotting weeds would have noticed that some undesirable plants have been gradually increasing along the Desert Road corridor between Taupo and Waiouru.

Stopping the insidious spread of weeds across vulnerable landscapes, for which multiple parties are responsible, presents many challenges, which often means the weeds get the upper hand. A workshop was held recently at the Department of Conservation’s (DOC’s) Turangi office. The workshop was led by Richard Hill (Richard Hill & Associates) on behalf of Landcare Research, and brought together staff from eight organisations responsible for managing weeds along the Desert Road corridor. The objective was to determine whether there was a joint opportunity to limit the spread of leguminous weeds in the area before it is too late.

The northern section of the corridor forms part of Tongariro National Park and has a distinctive ecological and landscape character. This is New Zealand’s oldest national park and now a world heritage site. The corridor includes the area known as the Rangipo Desert, which is a unique ecosystem containing volcanic dunes. Despite adequate annual rainfall (>1200 mm) the vegetation in the area remains low in stature due to the harsh winds, low humidity and coarse, sandy soils. Most of the native vegetation is in the form of tussocklands and dryland herbfields that support several threatened plants including Pimelea microphylla. Other exotic weeds being controlled by DOC and the army include: heather (Calluna vulgaris) and lodgepole or contorta pine (Pinus contorta). While a biocontrol programme is in place for heather and showing some good results, it still poses a threat. Mouse-ear hawkweed (Pilosella officinarum) and marram grass (Ammophila arenaria) are also unwanted invaders.

“The Desert Road has high natural values, both visually and in terms of biodiversity, but the integrity of the landscape is threatened by the spread of roadside weeds,” says Richard. Vehicles appear to be one of the main pathways for weed invasion. The park has had a long history of recreational use and is a popular place for rock climbing, fishing, hiking and skiing in the winter. Seed is transported on the underside of vehicles or on tyres which also disturb the ground providing suitable conditions for seed germination. Not to mention the drivers of the vehicles who sometimes carry a variety of seeds on their socks! Most vehicles are linked with state highway traffic, army manoeuvres, hunting, skiing, and (in adjacent areas) beekeeping.

The corridor is primarily managed by DOC and the Waiouru Military Training Area. Over the past 40 years the NZ Defence Force has managed pests and weeds to protect key values in the area. Other organisations with an interest in managing weeds in the area who attended the meeting, included the NZ Transport Authority, Waikato Regional Council, Rotoaira Forest Trust, Horizons Regional Council, Transpower and Genesis Energy. Despite previous and current efforts of the associated agencies to control existing and emerging weeds, legumes remain the big threat. Tree lupin (Lupinus arboreus), gorse (Ulex europaeus) and broom (Cytisus scoparius) all produce vast quantities of seeds that remain viable in the soil for decades. The meeting aimed to build on existing collaborations to come up with a better plan of attack.

Richard outlined the principles that are important when dealing with a woody legume invasion at a landscape level:

  • Once a long-lived seed bank has established, management plans must be sustained for decades.
  • It is vital to eliminate outlying flowering plants before they contribute to a significant seed bank.
  • Prevention provides a greater return on investment than local eradication, which in turn is more efficient than containment or management at a wider level.
  • Apart from eliminating outliers, prevention involves managing pathways of seed transport.
  • Legume weeds do not respect property boundaries. The answer to one stakeholder’s problem may well lie outside its jurisdiction. Collaboration is therefore essential, because once one member of a community has a problem, all do.

Richard stressed that controlling the invasion of long-lived weeds with long-lived seed banks is a difficult prospect requiring:

  • Spatially complex plans providing different solutions in different areas.
  • Long-term planning that can survive changes in land management regimes and staffing.
  • A single-minded and focused approach to operations.
  • Commitment and goodwill from the community involved.

Quentin Paynter presented information about the biology and ecology of broom with particular reference to the Desert Road. Quentin said that, due to its long-lived seed bank, broom had the potential to change ecosystem dynamics, displace native species and to persist in the landscape for a long time.

All of the participants agreed to develop a long-term, coherent plan for managing woody legume weeds across this landscape, and discussed the best approach. The four priorities identified by the workshop were closing knowledge gaps, addressing management of invasion pathways, gaining community agreement and participation, and undertaking sustainable operational planning.

Lack of knowledge about the distribution and density of each weed across the landscape was seen as a big barrier to acting collectively. These weeds can be reliably distinguished from other shrubs when flowering, so obtaining high resolution images of infestations was regarded as a priority. These will allow the weed threat to be quantified across the landscape, outliers identified for priority action, and baselines set for measuring change. Ground exploration will be required to validate some imagery, and to determine how well it represents the state of invasion. Other knowledge gaps identified were:

  • Limits to knowledge of the biology of the weeds, e.g. the ecology of tree lupin.
  • The true role of woody legume weeds in succession and vegetation dynamics in this environment.
  • The role of animals in dispersing seeds.
  • Best control practice in light of good knowledge of weed ecology, existing and new technologies.
  • How control tactics might affect future biodiversity and landscape values.

Invasion of uninfested land occurs through a variety of pathways, which will need to be managed. All potential pathways, high value sites or values that require priority protection, and sites that are of particularly high risk of invasion need to be identified and attention given to:

  • Managing risks around access points.
  • Hygiene measures to manage seeds on service vehicles and equipment.
  • Better understanding of the role of beekeeping in the dynamics of these weeds.
  • Better understanding the consequences of fi re for broom invasion and being ready to monitor and manage resulting invasions.
  • Managing watersheds to control outlying plants in headwaters that contribute to invasion downstream.

Finally, the participants agreed that a coherent long-term management plan will only succeed if it has the whole-hearted support of the local community. While gorse is generally perceived as a weed, the others are not, and as long as broom and tree lupin occur in just ones and twos in the environment the public is unlikely to appreciate their real threat. Early involvement of the community was seen as vital to promote information-sharing and behaviour change, such as early removal of outlying plants. There is a clear role for local businesses as well as tramping clubs and other organisations that make up the community of interest.

Since this workshop the participants have begun the planning process by obtaining aerial photos and data on the weeds’ distributions. A further meeting is planned to develop governance structures, a common vision, to discuss options for delivering that vision, and to discuss avenues for future funding. It will be a big challenge to put together a plan that will last the decades necessary to beat these weeds. We can only hope that something that started as a modest workshop will lead to a powerful joint initiative that can save the unique values of the Desert Road, and serve as a model for others facing similar challenges.

The workshop was organised with the assistance of Horizons and Waikato Regional Councils, with funds from an Envirolink Small Advice Grant (HZLC88) awarded to Horizons Regional Council.

Richard Hill