New Zealand’s current growth model is approaching its environmental limits, largely due to intensification of land use. Our biodiversity is under threat according to an OECD report on our environmental performance. The report recommended land management measures to reduce water pollution, and a broadened use of economic instruments to provide incentives for conservation on private land. Extinction rates for our native fauna are among the highest in the world.

In addition to this, we will continue to see intense weather events which highlight major issues with clear-fell forestry operations in sensitive steepland catchments. The plantation forest industry’s social licence to operate is under question – there have been persistent calls for vulnerable hill country to be established in native forest.

Putting Nature into the economic equation

Ecosystem services are defined as the benefits people obtain from ecosystems, or ‘natural capital’. This is an anthropocentric construct to help factor the value of ecosystems into the economic equation – to aid decisions about utilisation of natural resources, or undertake activities that may impact on ecosystems.

Non-timber values

Aside from timber production, New Zealand’s economy relies on forests for a myriad of non-timber values (NTVs), i.e., all elements of ecosystem services other than wood products.

Quantifying NTVs is vitally important for leveraging the business case for afforestation with native species. However, NTVs have largely not been factored into the economic value of forests because of the lack of awareness of the wider value of forests, as well as difficulty in tracking and quantifying the myriad of products and services.

NTVs in sustainably-managed native forests have been researched by the authors of this opinion piece. All statements are fully referenced in a much larger work. NTVs were evaluated under four main categories (note that there are overlaps with some values potentially falling into more than one category).

(i) Non-timber forest products

Industries associated with non-timber forest products are currently underdeveloped in New Zealand, except for mānuka honey, mānuka oil, and sphagnum moss. Many non-timber forest products are produced by small businesses that are often economically important for local communities and have potential for further development.

Non-timber forest products include:

• honey and other bee products (native forest species provide essential early-season nectar flow vital to the apiary industry)
• rongoā (traditional medicines), nature-based pharmaceuticals
• forest understory crops, including kawakawa
• wild foods, freshwater fisheries, hunting and trapping of wild game.

(ii) Environmental regulating services

Our economy relies heavily on forests (natural and planted) for environmental regulating services. However, they are widely regarded as ‘free of charge’ or a ‘gift of nature’.

These ecosystem services include:

• carbon sequestration – the only environmental service currently monetised
• habitat provision and enhanced biodiversity values (in terrestrial and aquatic environments)
• services provided by urban trees, including air quality, green infrastructure, and climate regulation
• stabilisation of soils, erosion reduction, catchment protection, and coastal buffers
• retention of nutrients, nutrient recycling, and water quality
• pollination services  – vital to the horticultural industry
• green firebreaks and fire risk reduction.

(iii) Socioeconomic, cultural and spiritual services

Forests provide general amenity and ambient environments for outdoor recreation and tourism, and have important spiritual and cultural values. Natural environments and native species underpin our unique sense of place and our international reputation. However, these services are particularly difficult to quantify in economic terms.

These ecosystem services include:

• ambient environments for tourism (particularly ecotourism), outdoor recreation, hunting, fishing, and wild foods
• cultural values associated with native forests, including conservation of native species and kaitiakitanga, rongoā, mahinga kai (traditional food sources), and tūrangawaewae (sense of place)
• aesthetic/landscape values
• native trees, green space, and human well-being in urban areas
• forest-based livelihoods and training opportunities
• ‘Clean, Green’ NZbrand image, political and commercial reputations.

(iv) Underlying supporting services

The original concept of ecosystem services includes supporting services that underlie the rest of ecosystem services. This includes photosynthesis and soil formation, and several other services that overlap with environmental regulating services, including water and nutrient recycling. Care needs to be taken to not ‘double count’ overlapping ecosystem services.

The benefits of weaving native forest back into our rural landscapes

Sustainably-managed native forests deserve a much higher profile as an economically viable land use in New Zealand. This could legitimately be achieved with the inclusion of NTVs in economic analyses.

While many NTVs can be attributed to forests irrespective of whether they are native or exotic, in most cases, the aggregated NTVs of native forests would likely be greater than that for exotic plantation regimes – particularly for cultural and spiritual values, conservation of indigenous biodiversity, and protection of erodible land, water quality, and downstream infrastructure and ecosystems. Permanent native forests managed solely for NTVs or sustainably managed under continuous cover regimes, are likely to have the highest aggregated NTVs, which could potentially exceed timber values.

Native forests in riparian areas are likely to have the highest aggregated NTVs because of the following services:

(i) buffering of the negative impacts of plantation forestry operations, intensive agriculture and urban development through prevention of sediment loss, recycling of nutrients and protection of water quality;

(ii) decreased run-off and flood peaks, protecting downstream infrastructures;

(iii) increased biodiversity and cultural values due to habitat provision, creation of wildlife corridors, protection of aquatic habitat and traditional food sources;

(iv) creation of connections between ecosystems to enable seasonal migrations;

(v) pollination services for adjacent horticultural and agricultural industries; and (vi) increased landscape aesthetic values.

The integration of sustainably managed native forests into rural landscapes provides opportunities for new and more appropriate primary production and business models for the future. For example, native forest could be woven back onto steep, erodible slopes and riparian areas on farms for all the benefits they provide. This could include sustainable harvest of high-value timber via continuous cover forestry regimes, while retaining the environmental and cultural services associated with high forest.

The farming community has come under increasing pressure regarding social licence to operate and is subject to increased regulation by local and central government. Restrictions on land use and nutrient run-off have recently been introduced to improve and protect water quality. Bringing native forest back onto farms – particularly in riparian areas and on erodible, marginal land – will improve environmental outcomes and regulatory compliance.

The draft advice from the Climate Change Commission recommends establishing new permanent native forests on steep, marginal farmland to offset the long-lived gas emissions in sectors with limited opportunities to reduce emissions from 2050, e.g., offsetting nitrous oxide emissions from agriculture. The Commission also recognises the many other benefits that this would bring, including improving water quality and erosion prevention.

NTVs in native forests on private land are currently difficult to monetise, other than carbon sequestration and some non-timber forest products such as mānuka honey. There is the conundrum of ‘valuing the invaluable’, i.e., NTVs with no direct material benefits and therefore difficult to incentivise, but critically important, nonetheless.

Incentivising native forestation – who benefits, who pays?

The One Billion Trees Programme signifies that the New Zealand Government recognises the wider value of forests; to date they have  committed to funding two-thirds in native species. Also, amendments to the NZ Emissions Trading Scheme (ETS) have strengthened the carbon market, providing greater incentive for all types of afforestation. However, native forests have been handicapped by the ‘one size fits all’ MPI look-up tables, which in some circumstances under-estimate the carbon sequestration by  native species.

Protecting existing forest and increasing permanent forest cover are recommended as top priorities for climate change mitigation and adaptation in New Zealand and globally. In their draft advice, the Climate Change Commission recommended a shift from clear-fell radiata pine to permanent native forest in erodible hill country.

There is also the well recognised problem of under-representation of lowland natural ecosystems in the conservation estate, due to intensification of land use for agricultural and urban development . And the value of forest cover for human well-being in urban areas has increasingly become recognised. Aside from the many environmental and cultural benefits, there is scientific evidence that access to green spaces makes us happier and healthier.

Weaving more native forest back into our rural and urban landscapes will greatly benefit New Zealand’s economy and human well-being, as well as Papatūānuku. However, there is the question of ‘who pays, and who benefits?’ 

While in general, the majority of costs associated with establishing and managing native trees on private land fall to the landowner, the benefits of NTVs often accrue to a much wider community, including:

• locally, e.g., amenity services such as shade and shelter, increased soil stability, biodiversity enhancement, hydrological services, and landscape aesthetics
• catchment-wide, e.g., reduction in erosion and sedimentation, improved water quality and water flow regulation, and increased resilience to intense weather events including protection of downstream infrastructures and ecosystems, and biodiversity enhancement
• regionally, e.g., catchment protection, biodiversity enhancement, increased tourism and employment
• nationally, e.g., accumulative benefits associated with all the above mentioned NTVs, and New Zealand’s international branding as a clean, green country
• internationally, e.g., carbon sequestration and mitigation of climate change.

There is a compelling argument for compensating the efforts of private landowners who safeguard biodiversity in the wider public interest, which is the flip side of the ‘polluter-pays’ principle.  Native forests generally support a greater biodiversity of indigenous fauna and flora than exotic forests, with most fruit and nectar feeders largely dependent on native forest for habitat. Currently efforts are underway to create a biodiversity credit system to incentivise establishment of native forest in New Zealand.  Initiatives to increase biodiversity values will likely drag other NTVs up as well.

The opportunity for New Zealand is to incentivise afforestation with native species on privately owned, rural working lands, and reward landowners for providing NTVs, particularly with the high cost associated with successfully establishing and managing native forest. The models to do this urgently need to be developed.

The Climate Change Commission recommends that the Government implement measures to incentivise establishing and maintaining at least 16,000 hectares of new permanent native forests per year by 2025, increasing to at least 25,000 hectares per year by 2030. These levels of new planting could be assisted by extending grant schemes such as One Billion Trees or by developing ecosystem services payment schemes.  Another longer-term option is to invest in research and development in continuous cover forestry regimes, and development of a sustainable niche timber industry for high-value, farm-grown native timbers.

Dr David Bergin

Dr. Jacqui Aimers

Gerard Horgan

We have seen the carnage play out across the media. The Canal Road site in Avondale, Auckland,  initially contained a grove of over 40 mature native trees, including black maire, kawaka, manoao, rewarewa, tōtara and pūriri. Despite vigorous protests and multiple arrests, all of these native trees have been felled since the section was sold to developers

Auckland’s urban tree loss has been under increasing scrutiny over recent years, with arborists describing it as a ‘chainsaw massacre’.

How can this happen? Changes to the Resource Management Act (RMA) in 2012 by the National-led government at the time, led to the removal of blanket tree protection of trees in 2015. This means that trees without formal protection on private land can legally be removed, regardless of their age or their biodiversity values. Developers have rushed to take advantage of this across Auckland, leading to the loss of many trees.

Auckland’s average tree cover is only 18.4%, which is moderately low relative to comparable international cities, so any loss of trees is concerning.

How can we quantify the value of urban trees and use this to leverage their protection?

The benefits of urban forest

Urban trees provide a myriad of benefits related to environmental services, cultural values, community health and well-being. New Zealand is one of the world’s most urbanised countries, with 86% of the population in cities and towns.

Trees on public land are particularly important in New Zealand because they generally have much better protection than trees on private land, as there is less risk of conflict with housing and infrastructure initiatives. This is particularly relevant since the changes to the RMA removed blanket tree protection. Also, more people have access to the benefits of urban trees on public land, which are even more important in neighbourhoods where there are high population densities and higher levels of socioeconomic deprivation.

In a study of the perceived value of urban trees in New Zealand, the benefits of aesthetics, having Nature in the city, habitat for wildlife, and fresh air, were rated ‘important’ or ‘very important’ by over 80% of respondents. Shade, carbon storage and protection from wind and noise were rated important or very important by 60% to 70% of respondents. Out of the seven listed negative effects, only one registered a higher level of importance (62%) than the lowest-ranked benefit, i.e., ‘causing drainage problems’.

Climate moderation

Not only do trees sequester carbon and mitigate against climate change, they also provide shelter and ameliorate the local climate. Trees provide shade, protect people from harmful ultraviolet radiation and reduce the risk of heat stroke. And the cooling effect of trees, due to evapotranspiration and provision of shade, reduces the urban heat island effect.

Brisbane is probably the leafiest city in the world, with an astonishing 44% tree cover, much of which is on public land. Its urban forest stores an estimated 1.9 million tonnes of carbon. And tree canopy cover makes leafy parts of Brisbane up to 7 °C cooler than treeless areas.

Green infrastructure

Lack of natural vegetation in urban areas reduces interception and ground infiltration of precipitation. This increases the speed of run-off and the risk of flooding. Green infrastructure counteracts this, taking pressure off downstream stormwater systems, alleviating flooding, and protecting water quality.

Green infrastructure is created by either strategically retaining natural vegetation in urban planning, or by planting trees and restoring wetlands, as opposed to creating man-made infrastructures. It is effective, economical, and has many other benefits that enhance quality of life in urban areas. These natural systems often perform more efficiently and are more cost-effective than manmade ‘hard’ infrastructure solutions.

Improved air quality and health outcomes

Trees and other vegetation are also effective in the interception of airborne particulate matter (PM) and absorption of gaseous air pollutants, resulting in improved air quality and lower incidences of respiratory and cardiovascular diseases, fewer hospital admissions and lower health costs.

The many tonnes of air pollutants estimated to be removed by urban trees in Christchurch and Auckland are worth tens of millions of dollars in terms of health benefits, largely due to reduced exposure to PM.

A recent New Zealand study demonstrated that exposure to natural vegetation can protect against asthma in children. This was based on a longitudinal study of 49,956 New Zealand children born in 1998 and followed up until 2016. Children who lived in greener areas were less likely to be asthmatic. Exposure to a greater number of natural vegetation-cover types provided an additional increment of protection; however, exposure to gorse and exotic conifers was found to be a slight risk factor for asthma.

Biodiversity values

Cities are often biodiversity ‘hotspots’ because they frequently sit astride convergences of several biomes. Remnants of natural vegetation commonly remain in gullies, floodplains and aquifer protection zones. These remnants provide habitat for species and help provide ecological corridors connecting the mountains to the sea.

While many ecosystem services may be provided equally, or sometimes better, by introduced tree species in urban settings, it is native biodiversity that underpins New Zealand’s unique sense of place (e.g., silver fern), cultural values (e.g., harakeke), and adds to tourism, international obligations and New Zealand’s reputation.

Urban trees, cultural values, and well-being Spiritual and cultural services

Cultural and spiritual services provided by urban forests are difficult to value economically but are highly valued by most urban residents and contribute significantly to quality of life, social capital, and mental well-being.

Our identity suffers when recreational opportunities and connections with Nature are lost, natural ecosystems are degraded, and native species become locally extinct. Volunteering in ecological restoration and involvement in activities in natural areas benefits health and well-being and is a unifying force in communities.

Nature is important for our well-being

In 1984, a pioneering clinical study showed how Nature influences our well-being. The recovery rates of patients after surgery were compared relative to their views from their hospital rooms. Some patients looked out to a garden and grove of trees, while others had a view of a brick wall. Patients with a natural view spent fewer days in hospital and used less medication.

Since then, there has been a wealth of international research on the importance of Nature for human well-being. A review of international epidemiological studies found evidence for a positive relationship between green space and population health. People living in urban areas tend to experience more stress and have poorer mental health. However, green space in urban areas helps counteract this by providing a restorative environment that alleviates stress and mental fatigue. This has important economic implications because a healthy population is more productive and has lower health costs.

Ecotherapy is an increasingly popular treatment programme that utilises the restorative effects of green space to benefit mental health and well-being.

Researchers in two clinical studies provided scientific evidence of the positive effects of walking in Nature on well-being, compared with walking in a purely urban setting. Even sitting in a room with views of trees resulted in a rapid decline in diastolic blood pressure, compared with sitting in a viewless room. These results suggest that having access to natural areas may be vital for mental health in a world that is rapidly urbanising.

The bigger the better – mature trees provide more benefits

Many of the benefits attributed to urban forest are disproportionately provided by larger, mature trees because:

• they create more shade
• they intercept larger amounts of particulate pollutants and absorb more gaseous pollutants
• they intercept more rainfall due to larger leaf areas and assist with the reduction of volume and rate of surface water run-off entering the drainage system
• they contain more carbon and generally have higher carbon sequestration rates
• residents often have strong emotional connections to landmark mature trees and are more likely to mourn the loss of large trees
• they provide better habitat and biodiversity values; and some native species, such as kākāand bats, prefer taller trees
• they are less susceptible to vandalism and can be pruned to provide higher canopy clearance over roadways and footpaths
• they contribute more to calming and slowing traffic on local streets than small trees

Retention of existing, larger-growing trees should be a priority, particularly in densely built-up areas where the associated benefits are high, and opportunities are limited for new plantings.

Dr. Jacqui Aimers

The reality of climate change

Burning fossil fuels has caused elevated levels of carbon dioxide in our atmosphere – more than can be absorbed by the world’s greatly diminished forests. Carbon dioxide and other greenhouse gases trap heat in the lower atmosphere, driving global warming. Carbon dioxide levels are now at their highest in human history.

The current forested area in New Zealand represents a reduction of over 70% from the pre-human state circa 800 years ago. This large-scale deforestation has been disastrous for our soils, our water, and our biodiversity and has been a source of emissions.

The World Economic Forum recently estimated that natural climate solutions, i.e., investment in conservation, and land use that increases carbon sequestration and reduces emissions, can provide one-third (almost 7 Gt CO₂₎ of the net emissions reductions needed to obtain a 1.5 to 2.0°C pathway by 2030. This would simultaneously address multiple other environmental issues, providing substantial co-benefits for the environment and associated communities.

In New Zealand, weaving our ngāhere (native forest) back into our landscapes will aid climate change mitigation and adaptation, as well as improving water quality, soil stability, and biodiversity conservation. However, climate change is inextricably linked with other compounding environmental crises threatening natural ecosystems, i.e., biodiversity loss, invasive weeds, pests and pathogens, and biosecurity incursions. There is no simple fix as each of these threats is complex to address, let alone the compounding interactions.

So how can we successfully establish and manage our ngāhere in the face of these threats?First, we need to understand how these intertwined crises are impacting the health of existing ngāhere and the establishment of new native forests. And then we can undertake measures to make our ngāhere more resilient.

Predicted changes in New Zealand’s climate include:

1. 1. • Warmer air and water temperatures.The average air temperature has already increased by 0.9°C with a predicted further increase of 0.7 – 1.0°C by 2040.
      • Increased intensity of extreme weather, i.e., more intense storm events.
      • Increased severity and frequency of drought– particularly in the already dry northern and eastern regions.
      • Significant changes in rainfall patterns, including a rise in extreme rainfalls, decreased rainfall in the north and east, and increased rainfall in the south and west.
      • Sea level rise– a 14 to 22 cm increase from 1916 to 2016, with predictions of further increases for centuries to come.
      • Increase in extreme wind speeds – particularly in the southern half of the North Island, and throughout the South Island.

Climate change will have varying effects across New Zealand, so it is important to understand regional impacts. NIWA has published climate projections at the regional level, and many other reports are available.

Climate change and native forests – impacts and solutions

Most of the research in New Zealand on forestry-related impacts of climate change focuses on exotic plantation forestry. However, several findings are relevant to our native forest:

1. 1. • pest numbers, pest distribution and incursions of new pests will increase, as will the costs of pest management
      • fire risk will increasewith hotter, drier conditions, plus an increase in available fuel due to an increased occurrence of weeds and mortality caused by increased pests and diseases
      • extreme weather events will lead tomore erosion on steep and unstable slopes; highlighting the risks associated with some land uses, including clear-fell forestry regimes
      • increased wind and storm damage to forests are likely.

Protecting existing forest and increasing permanent forest cover are recommended as top priorities for climate change mitigation and adaptation in New Zealand (Climate Change Commission 2021) and globally. This will also capture co-benefits of biodiversity conservation, protection of soils, and better water quality.

Our ngāhere plays an important role in climate change adaptation, particularly:

1. 1. • green fire breaks and fire-resistant ngāhere– countering the increased risk of wildfires
      • prevention of erosion and landslides – even more important due to more frequent extreme weather events
      • riparian areas, green infrastructure and flood protection– riparian vegetation decreases peak flows and moderates flood events. Green infrastructure utilises natural and restored ecosystems, as opposed to manmade infrastructures, to take the pressure off downstream stormwater systems, alleviating flooding, and protecting water quality in urban areas
      • coastal buffers– indigenous coastal forest buffers provide sustainable and effective permanent barriers mitigating the effects of sea level rise, and salt and wind damage. Unfortunately, natural coastal vegetation has been cleared from much of our coastline, with almost total removal of dune fores

There are significant knowledge gaps in how climate change will impact forests in New Zealand and globally. However, there is already evidence that climate change has contributed to forest dieback in other countries, altering the composition and structure of forests and the distribution of species. Because of the speed of climatic changes, species may not have time to adapt to the new conditions. Profound changes in the composition of some ecosystems could occur and there may be significant latitudinal and altitudinal shifts of vegetation zones. Tree mortality and growth reductions could even transform forest ecosystems from carbon sinks to carbon sources.

In New Zealand, climate change has the potential to destabilise the natural distribution and patterns of abundance of our native species. 

Maintaining a healthy ngāhere is the best defence!

Stressors such as invasive weed species, pests, disease, loss of ecologically key species, and degradation and fragmentation of ecosystems tend to amplify the sensitivity of ecosystems to climate change.

It is more important than ever to get the basics right, as described in Dr David Bergin’s Ten Golden Rules of Native Species. This includes thorough planning and working with Nature to encourage natural regeneration, or if planting new areas, ensuring you have good quality, eco sourced planting stock.

Mitigating the impact of drought and heat

Recent droughts, including the 2019/2020 summer drought, have resulted in tree mortality in many affected areas. We can expect to see more, and more intense droughts in the future, particularly in northern and eastern regions of the North Island and eastern regions of the South Island. Time spent in drought could double by the middle of the century. Healthy, established forests are generally more resilient to drought, whereas recent plantings are more vulnerable as they are more exposed to the weather and developing root systems do not have access to deep-soil-water stores.  Again, practitioners establishing new native forests need to be conscious of the threat of drought, and follow best practice guidelines.

Green fire breaks and fire-resistant ngāhere – defence against wildfires

Wildfires have always occurred, but predictions of increased fire risk associated with climate change mean that extensive wildfires such as those experienced in Port Hills (2017) and Pigeon Valley ( 2019) are likely to become more common.  However, fire danger in some areas will remain unchanged or even decrease due to increased precipitation.

Healthy native forest is quite resistant to all but the most intense fires because the understory is thick with shrubs, ferns, seedlings, saplings, lianes, epiphytes, mosses and liverworts. We all know what it is like to walk into intact native forest on a hot, dry day – a microclimate of cooler, moist air is created by shade and evapotranspiration.

But in many areas, the bush is often an eaten-out remnant of what was once a self-sustaining forest, and has a lot of standing deadwood and dried fern fronds. With pest control and fencing, the understory can begin to re-establish and fire resistance will improve.

Green fire-breaks can be a tool to help slow or even stop the spread of wildfires. These strips of low-flammable plant species can be grown at strategic locations in the landscape – such as in wildland-urban interfaces, around homes and buildings in rural settings, in shelterbelts, or interspersed throughout plantations of more flammable species. Not all plant species burn the same but many native species have low flammability and are suitable for green firebreaks. (Note that some native species are highly flammable, particularly mānuka and kānuka).

Extreme weather, disturbance and our ngāhere

Extreme weather can cause disturbances such as landslides, windthrow, and flood events. Disturbances are natural phenomena that have impacted our ngāhere for millennia. Before human intervention, native pioneer species would quickly establish in any canopy gaps or on bare soil. However, introduced pests and invasive weeds interfere with the natural regeneration processes. And climate change will create more disturbances due to an increase in extreme weather.

This is likely to have an impact on the population dynamics and composition of our native forests. And carbon sequestration will be reduced if forests fail to regenerate quickly, or fail to regenerate at all. Assistance with forest regeneration after disturbance may be necessary, particularly pest and weed management, and possibly supplementary planting.

Complex multi-aged, permanent forest, or uneven-aged forest managed through single-tree selection, is likely to be more stable in high winds compared with even-aged plantations.

Climate change and our biodiversity crisis

Most of our indigenous flora and fauna are endemic (i.e. only found in New Zealand) and many are highly unique having evolved in geographic isolation for millions of years. This unique biodiversity was already under considerable threat before climate change was added to the equation. Our species extinction rates are among the highest in the world. The main threats are habitat loss, fragmentation and degradation of ecosystems, invasive weeds, introduced predators and pests, and new incursions of pathogens.

Intact, structurally complex, species-rich forests are more resilient in the face of climate change and are better at delivering a myriad of ecosystem services including carbon sequestration. Conversely, loss of biodiversity can reduce the resilience of forest ecosystems, making them even more sensitive to the effects of climate change.

To date, climate change has had relatively modest effects on ecosystems and biodiversity in most parts of the world, compared with other anthropogenic actions, but this is likely to change over the coming decades. In New Zealand, threats such as invasive pests and weeds, habitat loss, and disease are thought to pose more serious risks in the short to medium term than climate change. Damage by browsing pests, such as possum, deer, and goats, can cause regeneration failure of palatable tree species and diminish the value of the forest for habitat, further diminishing the biodiversity of indigenous wildlife and plant species.

Ongoing management to control invasive weeds and pests is required. Some sites will also benefit from enrichment planting of tree species where there are no nearby seed sources. We need to weave indigenous biodiversity back into our productive rural lowlands and urban areas to counter the under-representation of lowland ecosystems in the conservation estate. Restoration of riparian zones is particularly beneficial as this restores terrestrial and aquatic biodiversity, helps link fragmented ecosystems and create ecological corridors, improves water quality, and contributes to climate change adaptation and mitigation..

Strategic measures for sustaining indigenous biodiversity in the face of climate change are summarised in a Manaaki Whenua − Landcare Research report:

• continue to reduce the pressure from pests, weeds and pathogens
• protect, buffer and restore our remaining ecosystems, including in modified landscapes
• ensure connectivity between ecosystems and habitats to enable migrations and allow ecosystem adjustment so species can find viable niches as the climate changes.

Pests, weeds, diseases, and climate change

Due to increased global trade, a warmer climate, and greater disturbance, we are facing more biosecurity threats, i.e., increased risk of incursions of pests, weeds and pathogens. A warmer climate means that biosecurity incursions from subtropical and tropical regions are more likely to become established in New Zealand. And currently established pests, weeds, and pathogens are likely to change their habitat ranges and population size and become more of a threat to our native biodiversity due to climate change.

New Zealand likely has one of the best biosecurity systems in the world, but there is little investment in protecting native forests from pest and disease incursions. The recent incursions of kauri dieback and myrtle rust have demonstrated how vulnerable our native species are – these pathogens are having widespread and devastating impacts on iconic forest species and the ecosystems they support.

Protecting our ngāhere against pest and disease

It is imperative that any new potential unwanted pests and pathogens are thwarted at our borders.  This includes pathogens that present even more serious threat to our myrtle species than the myrtle rust strain already in New Zealand.

Biosecurity measures must be upheld from nursery propagation through to planting and forest management. Biosecurity New Zealand has advice on how to find, report, and prevent pests and diseases  Advice is also available for current incursions. The Kauri Dieback Programme has guidelines including a kauri propagation and planting guide. The Myrtle Rust in New Zealand website also provides good information and resources.

We need to be more committed than ever to pest and weed control. Control of pests not only helps restore the health of our ngāhere, protecting palatable species and forest regeneration, it also allows our vulnerable indigenous fauna a chance to survive and thrive. Predators have had a devastating impact on our indigenous wildlife. And high numbers of introduced browsers open up the understory, drying out the forest making it more vulnerable to pests and diseases, and providing opportunity for invasive weeds. Invasive weeds impact through competition and changes in ecological associations, and prevent regeneration of native forest.

Germplasm conservation must be considered for species under dire threat. This includes seed banking and conservation plantings of the species outside of their natural range, in locations where there is less threat. This is particularly important when a lethal disease or pest incursion is difficult to control and is likely to overlap host species’ natural range, such as with Phytophthora agathidicida (PA) and kauri, and with myrtle rust and several of our vulnerable myrtle species.

There are biological, aesthetic and cultural concerns about planting species away from their natural range; however, in the face of potential extinction, drastic action is warranted.

Seed banking is helping to ensure the long-term future of our myrtle species. Seed has been collected from our native myrtles throughout New Zealand as an insurance policy – preserving the genetics of our myrtle species in the event of myrtle rust spreading throughout New Zealand and potentially causing extinctions.

Conclusions

Bold policymaking, advances in science, and the goodwill of stakeholders can help weave more ngāhere back into our landscapes, helping New Zealand to become carbon neutral by 2050, while simultaneously resolving multiple other environmental crises. Measures of success will include restored ecosystems, better recognition of the importance of natural resources, improved biodiversity values, reduced erosion, cleaner water, greater resilience to climate change, and contribution to world efforts for a more stable climate.

There are significant knowledge gaps in how climate change will impact native forests and what management practices will assist in increasing resilience. This is an urgent area of research, considering the recent recommendations of the Climate Change Commission to significantly increase native forest cover. Research needs to be targeted at understanding and managing the increased risks associated with climate change.

Research and action are urgently needed on:

• the cumulative and cascading impacts of climate change and the other intertwined stressors, including biosecurity incursions
• the impact on ecosystem function and ecosystem services, such as carbon sequestration; and risk management and mitigation measures to make our ngāhere more resilient.
• germplasm conservation measures for kauri and vulnerable myrtle species.
• integrating our ngāhere into risk mitigation and adaptation strategies, e.g., green firebreaks, coastal buffers, riparian buffers, and green infrastructure.
• communicating research findings so that appropriate policy is generated, and stakeholders’ needs are met, especially those doing the mahi of forest establishment and management, and those funding it.

Maintaining a healthy ngāhere is the best defence! It is more important than ever that we get the basics right and follow best practice in establishing and managing our ngāhere. The ultimate goal is ensuring that we have structurally complex and species-rich forest ecosystems that are resilient in an era of climate change.

Dr. Jacqui Aimers