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A “pervasive and ongoing invasion” of radiata pine – Expert Reaction

New research says invasive radiata pine is spread more widely across NZ than was previously appreciated, with modelling showing that up to 76% of the country’s land is climatically capable of supporting populations of the trees.

The authors say their findings demonstrate “pervasive and ongoing invasion of radiata pine outside plantations”, with more work needed to manage current invasions and prevent future ones. They recommend a levy on new non-native conifer plantations to offset costs of managing invasions, and stricter regulations to protect vulnerable ecosystems.

The SMC asked experts to comment.

Dr Cate Macinnis-Ng, Associate Professor and Rutherford Discovery Fellow, University of Auckland; and Principal Investigator and Theme Co-Leader, Te Pūnaha Matatini, comments:

“Radiata pine invasions have a significant impact on natural ecosystems in Aotearoa. They change the biodiversity and ecosystem services of invaded areas. This research has looked at currently invaded sites and uses projections of climate change to determine areas that may be invaded under future climates.

“The work identifies three types of uncommon ecosystems that are already invaded – geothermal, gumlands and inland cliffs, scarps and tors. These uncommon systems often include rare plants and other organisms so have high conservation value.

“Invasions of radiata pine will also change ecosystem processes such as carbon uptake and storage and water cycling, even in ecosystems that are more common. Therefore, more intensive management of invasions and prevention of future spread is a very important next step.”

Conflict of interest statement: “I have an active collaboration with lead author Peter Bellingham and have collaborated with some of the other authors in the past.”  

Professor Euan Mason, New Zealand School of Forestry, University of Canterbury, comments:

“The authors have done a good job identifying where radiata pine will grow, and also the instances where it is a wilding problem. Ability to grow and ability to reproduce are not the same thing, however. Natural regeneration of radiata pine is much more severely restricted by frost than that of other, more problematic wilding species such as lodgepole pine, Corsican pine, Douglas fir and Scots pine. It is also intolerant of shade and will not prosper under an existing forest canopy. This means that radiata pine is much less likely to be a wilding problem in the high country, even on open sites, where low grazing pressure often favours wildings of other species. Moreover, on unforested, lower elevation, warm, wet sites where it might reproduce easily, high grazing pressure on neighbouring properties usually keeps it in check.

“However, there are instances, as identified in the paper, where grazing pressure is low on warm, wet, open sites, and in those places radiata pine wildings can be problematic. About 90% of our exotic plantation area is occupied by radiata pine, and as a proportion of plantation area, it is much less frequently a wilding problem that those other, more hardy species, some of which are gradually spreading across our high country. People who plant trees that reproduce as wildings on neighbouring properties should be held responsible for the control of those wildings. Imposing a levy on all exotic plantation owners for the control of wildings that have emerged from just some of the planted area, and most commonly from species that are only rarely planted, would be unfair however.”

No conflicts of interest.

Dr Sarah Wyse, Lecturer in Forest Ecology, School of Forestry, University of Canterbury, comments:

“In my opinion this paper is a very valuable, and timely, and much needed review of the ecological threats posed by Pinus radiata to many native New Zealand ecosystems, and represents an exhaustive and thorough review of the topic.

“The authors phrase nicely that there is ‘a view that [Pinus radiata] is relatively unimportant as a biological invader’. This view is likely to have arisen perhaps from an assumption that wilding conifers are an issue of the high country, where there are large tracts of vulnerable land. In such habitats, other conifer species are indeed worse than radiata, being more suited to the climate and having been planted in abundance in those areas. Radiata, in contrast, is often planted surrounded by landscapes that are less vulnerable to invasions, such as highly managed landscapes, farmland with high stocking densities, or native forest.

“However, as the authors illustrate, radiata certainly has the ability to pose quite a threat to vulnerable habitats such as sand dunes, gumlands, geothermal communities, and systems in the early stages of forest successions (e.g. following a fire or other disturbance) if they are nearby.

“We also need to recognise the lag phase in biological invasions: species do not invade as soon as an individual is introduced to an area. The authors discuss the effects of residence time on our view of the species as an invader. A species that wasn’t a problem in the past can certainly become one in the future.

“As the authors highlight, radiata is structurally and functionally very different to the native plants of the ecosystems or successional stages that it invades, and it is therefore likely to have considerable effects on the ecosystems and future forest successions. As the authors discuss, the work is likely a conservative estimate of the current and potential future situation. Due to the nature of the modelling, which uses occurrence records of where the species has been recorded, they cannot over-estimate suitable habitat, but are likely to underestimate it if locations where the species is present simply haven’t been documented. Likewise, there may be other ecosystems impacted by radiata that have not yet been documented.

“I hope this work will encourage recognition that radiata is an invasive species in New Zealand, and that care and consideration therefore needs to be given to the landscapes in which we are planting it. If we are to expand our radiata plantations, particularly for carbon sequestration, we need to be very mindful of the threats posed by the species to vulnerable ecosystems. This work therefore provides much-needed evidence to help guide policy and management.

“Wilding conifers arising from plantations are considered under the National Environmental Standards for Plantation Forestry (NES-PF), however clearly the tools used to assess risk are under-estimating that from P. radiata in some key habitats as highlighted in this study. The paper therefore has some important implications for that assessment process, and for determining where forest managers need to ensure they are monitoring for and managing wilding pines arising from their radiata plantations.

“I strongly suspect that the levy suggested by the authors will not be well received by industry! In my view I think ecologists and the forestry industry need to think carefully about where we are siting plantations, and perhaps any incentives could best be used to encourage monitoring and management, and discourage planting near vulnerable habitats. We need to learn from our Southern Hemisphere neighbours who have been dealing with radiata as an invader for a longer period of time. Certainly, an area that I think is of particular concern is where carbon plantations may well be put into more marginal or inaccessible lands that are not economically suitable for timber plantations and potentially more vulnerable to wilding pine spread. As the authors point out, forest managers need to be aware that radiata is capable of long-distance dispersal, as has been observed in New Zealand and also widely reported overseas.

“The authors acknowledge the importance of the species for forest industry and New Zealand’s GDP, and are not saying that we should stop planting it by any stretch of the imagination. Likewise, in terms of carbon sequestration, it is one of the best tools in our tool box for rapidly sequestering carbon. But we need to be mindful of the wider context of the species and where we are planting it, and the ongoing monitoring and management that is required. Scion is engaged with work with Douglas Fir to reduce the seed production – such work would be valuable for radiata too.

“This paper highlights that we need to stop underestimating the capabilities of this tree as a wilding conifer.”

Conflict of interest statement: “One of the co-authors on the paper is my husband. Others on the author team are people I’ve worked with/are working with on other projects.”

Dr Tara Strand, General Manager Forests and Landscapes, Scion comments:

The paper is a useful additional to discussions on invasive species.  At a high level, it reinforces the challenge that we have with controlling wilding conifers in New Zealand ecosystems, some of which are already highly modified.  The Government has recognised this and established a National Wilding Conifer Control Programme to deal with this serious and growing problem, including through a $12.9 million 5-year programme of research that aims to achieve outcomes and tools for managing and mitigating wilding conifer invasions.

“The issue is much broader than just introduced conifers, and last November the Parliamentary Commissioner for the Environment made some good recommendations for a more integrated approach for how New Zealand might better manage weeds that threaten native ecosystems.  As the paper notes, propagule pressure from potentially invasive exotic species comes from a wide variety of non-commercial plantings right across the landscape, including those established to provide a range of ecosystem services. As such, a levy on new conifer forests may only address a proportion of a much bigger issue. Like the current National Wilding Conifer Control Programme, which focuses on all wilding conifers independent of their sources, a continued comprehensive approach is needed to address weeds that threaten New Zealand’s ecosystems and iconic landscapes.”

Conflict of interest statement: “Scion had a research programme under the Manaaki Whenua led research Winning Against Wildings and is now hosting the Vive la Résistance research programme.”