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Winning against wildings

Oct 2017 – Sept 2021
A research programme with funding from the Ministry of Business, Innovation & Employment (MBIE) Endeavour fund
The Winning Against Wildings research programme seeks to develop and integrate new knowledge of the causes and consequence of wilding conifer invasions, and the management interventions needed, to better manage wilding conifers.

The research is a collaboration between Manaaki Whenua, Scion (NZ Forest Research Institute), Lincoln University, and the University of Canterbury. The programme works in close partnership with the National Wilding Conifer Control Programme and the New Zealand Wilding Conifer Group.

The programme has several streams, grouped into three sections:

  1. Immediately applicable research – control methods, prevention to spread, and detection of wildings.
  2. Improved ecological understanding of wilding conifer invasions – impacts and legacies of these invasions, the risk of spread of a variety of species.
  3. Integrating research findings into long-term prioritisation and strategy for wilding conifer management.

The programme will have direct benefits to current wilding conifer management and will also assist the National Wilding Conifer Control Programme with meeting the goals of the NZ Wilding Conifer Management Strategy.

Main research streams

Manaaki Whenua is leading the Forecasting, Impacts and Legacies, and Social Research streams, and is involved in/a contributor to all of them.


Led by: Scion

The methods we use to control wildings can be grouped into two categories: mechanical removal such as hand-pulling or cutting down with chainsaws; and herbicide application, either by hand or applied aerially from a helicopter. Mechanical methods are effective, but access to sites can pose a challenge, particularly in steep or remote areas. In these instances, aerial application of herbicides is time and cost effective and also can be a safer alternative to sending out ground control crews.

Decreasing volumes while increasing the efficacy of herbicides

Herbicide trials conducted now use the knowledge and lessons learned from past management experiments. Our researchers are examining ways to decrease the volume of herbicides while increasing the efficacy. In controlled experiments, there is potential to reduce the amount of herbicides used for dense infestations without compromising efficacy. The next steps are to test herbicide mixtures with lower concentrations of active ingredients in the field on wilding trees, and to determine the optimal dosage of herbicide per tree size, since smaller trees need less herbicide.

How do we control moderate-density infestations?

The programme is also examining methods to treat areas of moderate-density infestations. This density of wildings has proven to be problematic for control strategies since controlling all these trees on the ground is very time-intensive. Researchers are exploring the possibility of using UAVs (Unmanned Aerial Vehicles) to control trees in moderate densities.


Led by: Scion

To control wildings in a landscape, we need to know first where the wilding conifers are.

There is a variety of remote sensing data available with different combinations of spatial and spectral resolutions. The finer the spatial and spectral resolution of remotely sensed data, the more it will cost. Therefore, we need to figure out the balance between cost of remotely sensed data aquisition, processing and effective detection ability.

Automating the detection of wildings in grasslands

Researchers at DOC and Scion have independently developed preliminary algorithms to detect wilding conifers in open grasslands. In these grasslands, dark-green conifers of a certain size are easily distinguishable from the background grassland vegetation. Both have determined the size of conifers they can detect with good accuracy with different remotely sensed datasets and modelling aproaches. DOC now is leading the development of a fully automated processing framework, which will allow the “plug-in” of more advanced models that are being developed by Scion under the programme.

Detecting wildings in more complex environments

At the same time, researchers at Scion are building on these initial results to help develop the right mix of sensors, platforms and models to allow the better and more accurate detection of wilding conifers in more complex vegetation types. This research will continue for the next two years and updates and models can be expected during that period.


Led by: Manaaki Whenua

Even if we know where the wildings are by detecting them remotely, we often do not have all of the money and resources needed to remove all infestations immediately. Instead, we have to prioritise control efforts. How do we decide where and when to control wildings when we have limited money and time?

How to reduce negative impacts of wildings

A recent study examined the trade-offs in wilding conifer management for impacts on biodiversity, landscape values, carbon storage, and erosion protection. While many impacts of wilding conifers are harmful (reducing biodiversity, landscape values, and water yield), some impacts are positive (sequestering carbon and providing erosion protection). This study examined the upper Waitaki catchment and found that areas with high biodiversity should be ranked the highest priority for management to reduce negative impacts of wildings. The study also found that only a small stand of conifers would be needed to provide erosion protection.

Current research will inform better management

Using data on dispersal, researchers have developed a spatial spread model to predict where wildings will establish and what their impacts will be in the future. These predictions will allow us to test different management scenarios to determine what is the most effective management strategy to reduce the impacts of wildings and maximise returns on our control money spent.

To trial how the spread model could be used for management planning, researchers discussed the model’s predictions with stakeholders in Marlborough as part of an Envirolink project. Two management scenarios were compared: containment (controlling new infestations spreading from existing seed sources) and removal (controlling existing wilding conifer infestations). The researchers found that containment costs increase drastically over time due to the constant need to clear sparse infestations. Therefore, removing dense infestations up front has a high return on spend, particularly in windy areas.

Researchers are now working on tweaking the model to take into account stakeholder suggestions. Next steps will be to use the predictions of this model to inform management strategies.

Reference: Mason NWH, Palmer DJ, Vetrova V, Brabyn L, Paul T, Willemse P, and Peltzer DA. 2017. Accentuating the positive while eliminating the negative of alien tree invasions: A multiple ecosystem services approach to prioritising control efforts. Biological invasions, 19 (4): 1181-1195.

Impacts and Legacies

Led by: Manaaki Whenua and University of Canterbury

Wilding conifers change the way an ecosystem functions. They affect the soil nutrients and cycling, thereby altering which plants would thrive in that area. They also co-invade with non-native mycorrhizal fungi, further changing soil function. While we know that wilding conifers impact ecosystems, we are not sure to what extent these impacts occur at different stages of invasion and nor do we know how long these impacts last.

What’s belowground comes around: Legacies in the soil

In a study in 2014, researchers found that wilding conifers have the potential to irreversibly change ecosystems. The results of this study suggest that wildings could have a long legacy belowground. Wildings increase nutrient cycling rates, increasing the availability of nitrogen (as nitrate nitrogen) and phosphorus in the soil, which leads to an invasion of exotic herbs and grasses following wilding removal. These results have large implications for restoration and management priorities because they suggest that we may not be able to plant the same species which were present in an area before wildings invaded.

Researchers at Manaaki Whenua and University of Canterbury are expanding upon this 2014 study and examining more closely the impacts and legacies of wildings. They are exploring whether there is a tipping point of impacts beyond which their effect is irreversible. Researchers are currently quantifying the timing and magnitude of these impacts, as well as quantifying changes in fire risk, carbon balance, and water availability. We expect to hear about initial results in 2020.

Related to this work, researchers are also quantifying the magnitude of legacies left by wildings and what effect these legacies could have on subsequent regrowth of conifers and other species. The goal of this research is to improve the success of restoration following wilding removal. If we know how the soil and belowground communities have changed, then we will be better informed about which types of plants will thrive in areas where wildings once were growing. We expect to hear about results of legacies in late 2020.

Reference: Dickie IA, St John MG, Yeates GW, Morse CW, Bonner KI, Orwin K, and Peltzer DA. 2014. Belowground legacies of Pinus contorta invasion and removal results in multiple mechanisms of invasional meltdown. Annals of Botany Plants, 6, plu056.


Led by: Scion

A key aspect of wilding management is the prevention of future spread.

Plantation placement

Because conifers used in forestry disperse their seeds by wind, the placement of plantations is crucial. A plantation in a high-wind area surrounded by vulnerable land threatens the native biodiversity and productivity of the land.

We used to think that there were take-off sites at the tops of hills – these take-offs site would be the areas where it is most likely for seeds to be transported by wind many kilometers. Researchers have now tested this theory using 3D modelling of hills and wind turbulence and found that this theory was incorrect. Take-off sites are on the windward slopes of hills. Using the results from this research, scientists from Scion will put together a decision support tool to assist managers with siting a plantation in the right place.

Surrounding land management: Grazing and fertiliser application to reduce spread

Another important aspect which can prevent or reduce the spread of wildings is land management around planted conifers. Grazing by sheep can control young seedlings before they become too woody; however, cattle have not been found to be effective at grazing wildings.

Fertiliser application can also reduce the establishment of wildings. Fertiliser increases the growth of grasses (often introduced), thereby out-competing wildings for light, water and nutrients. However, fertiliser application can lead to increases in native plant browsing and exotic species out-competing natives. Therefore, while fertilisers can reduce the number of wildings, its application can also reduce the number of native plants.

Conifer sterility and low-seeding trees

Another component of prevention is planting trees which produce low numbers of seeds or are sterile (i.e., produce no viable seeds). In the programme, researchers are exploring whether they can breed low seed-producing Douglas-Fir. They are also examining whether they can edit the cone-producing genes of Douglas-Fir to create sterile trees. We expect to hear results from this research in 2021.

Social Research

Led by: Manaaki Whenua

Wilding conifers affect people as well as the environment. Understanding how people’s values are affected by wildings will help us identify why people get involved in wilding control and prioritise where to focus our control efforts.

To dig deeper into the knowledge and views of wildings in rural communities, the Survey of Rural Decision Makers in 2015 and 2017 included a series of questions about wilding conifers. This survey found that in areas where wildings were being controlled, there was high awareness of the issue. Over time, awareness has increased as well, and more people saw wildings as harmful rather than beneficial in 2017 compared to 2015. Most landowners (83%) who had wildings on their land controlled them and said that control was easy and not expensive to do. When asked the reasons for why landowners undertook wilding control, stewardship/ kaitiakitanga, improving or maintaining pastures, and protecting native species/habitats all ranked highly.

The results of these surveys provide us with valuable information on landowners’ views of wildings, whether they undertake control themselves, and why they do. This information will enable us to provide better advice to rural communities and inspire more control efforts.

Future research in the programme will work on incorporating findings of these surveys into spread and management models to help us estimate the consequences of the spread of wildings and preferred management interventions. This research will help optimise control efforts to minimise costs and reduce negative impacts on social, environmental, and cultural values. We expect the see the results of this research in mid 2021.

Spread Risk

Led by: Lincoln University

Since the seeds of wilding conifers are dispersed by wind, there is inherently a risk of seeds spreading from planted conifers. However, not all conifer species pose the same risk of spreading; some conifer species are more prone to spreading than others.

The characteristics of a conifer’s winged seed determines a species spread risk, or how likely and how far seeds can spread. The conifers’ seeds have wings, and seeds with big wings are transported farther than seeds with small wings. While we used to think that heavy seeds would be transported less far than light seeds, this might not necessarily be correct. Recent research on Pinus radiata (radiata pine) suggests that for this species, seed wing size increases with seed weight, thereby enabling heavy seeds to still disperse long distances. This research is currently being expanded upon to examine more species than radiata to determine the spread risk. Other than the presence of wings on a seed, a tree’s age to maturity and producing seeds can also make it riskier. Pinus contorta can start to cone as young as five years old for example.

We do not know how much variation of spread risk there is within a species. In order to better inform our spread predictions, we need to quantify this variation in a species’ ability to spread. Current research in the programme is addressing this gap in our knowledge as well as using novel methods to improve our understanding of the spread risk between species. Already researchers have found that there is within‐species variation that affects our predictions of how far seeds are likely to disperse. These findings on variation of spread risk within and between species will next be used to update a spatial spread model. This model will tell us the range of where and how far trees could spread, thus informing our management strategies too.

Further information is available here: Wilding conifers website  

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