Issue 1, March 2010
In this issue:
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Editorial
Welcome to the first edition of MAF Update, our newsletter designed to inform you about research we are undertaking that may be of interest to MAF.
This newsletter is our response to discussions I have had with some of you about how we can communicate better – and in particular how we can better share news about our relevant research, using a suggested layout from some MAF staff.
Like MAF, Landcare Research is a diverse organisation. Our work covers the sustainability of land environments, biodiversity, and businesses and the primary sector. The land environments area on its own is broad. For example, as many of you will be aware, we are working to reduce detrimental impacts on soils, landscapes and water, as well as addressing the challenges of climate change and the control of invasive species.
One distinctive strength is our ability to work across scales – from the precision irrigation work with individual farmers mentioned in this edition, to catchment-scale projects such as the erosion control research we are doing with you on the East Coast, to our work with you over national policy, such as the ETS. Another of our strengths is the multidisciplinary nature of much of our research - we provide integrated solutions that can span different sectors.
So there is a lot happening and we are working together with different parts of your organisation on numerous areas of research.
I think that a regular bi-monthly e-newsletter touching on many aspects of that work and relevant other research can only benefit our relationship.
I hope you find this interesting. I would welcome your feedback.
Best wishes,
Phil Hart
Land & Water
Precision irrigation
Optimally matching the irrigation needs of a crop with the water-holding capacity of the soil is important for maximising production, reducing pumping costs, making best use of available water and preserving groundwater quality.
To achieve this, Landcare Research soil scientist Dr Carolyn Hedley has teamed up with the Palmerston North company Precision Irrigation to develop an innovative irrigation solution.
Dr Hedley uses a combination of electromagnetic (EM) induction survey and traditional soil sampling techniques to produce a map of the soil available water-holding variability of an irrigated area. An EM sensor fitted with accurate GPS is towed over the ground to detect differences in soil texture and moisture. Soil sampling confirms the differences in soil available water-holding capacity, and wetting and drying patterns are tracked in each zone using soil moisture sensors.
The accurate EM map and sensor information is then uploaded to intelligent Precision Irrigation software used to control lateral or centre-pivot irrigators. The modified irrigators have valves installed on each sprinkler. The software automatically controls individual valves so the optimal amount of water is applied as the irrigator moves over the land.
Application & benefits
Mid-Canterbury crop famer Eric Watson is using variable-rate irrigation to maximise crop production with a very limited water allocation. Farming next to the Ashburton River, the stony Rakaia soil on one side of his property (light blue on map, right) requires more frequent irrigation than the heavy Wakanui silt loam (dark blue on map) furthest from the river.
Previously, with the uniform application of water across his property, Mr Watson was averaging – applying too little water in some areas and too much of his precious water in others.
‘By utilising variable-rate irrigation our lateral delivered 30 mm of water on one part of the paddock (for early-sown beans on light soil) and just 15 mm over the other part (for spring-sown pak choi on heavy soils). This saved both water and money, and prevented over-watering of crops,’ says Mr Watson.
‘A big benefit of this system is that where we have 5 hectares of overlaps in our irrigation system, now we can shut off the nozzles that go over these areas.’
Variable-rate irrigation is also relevant for less variable soil types. Different crop varieties can be planted in different areas without worrying about irrigator paths. And Featherston dairy farmer Brian Bosch says sprinklers automatically shutting off when crossing laneways is saving about $10,000 in track maintenance and helping prevent cows from becoming lame.
Initial research suggests that water savings of up to 20% can be achieved through this solution. Proposed research will further investigate the energy and water savings possible, as well as resultant increases in crop production.
Spray systems make up about 70% of all irrigation systems in New Zealand and cover an area of about 600,000 hectares, up from 460,000 in 2004 (NZ Statistics).
Further information:
Carolyn Hedley
Improving lake water quality
Landcare Research science is providing independent, evidence-based support for the policy changes necessary to reduce nutrient levels in the Rotorua Lakes.
Environment Bay of Plenty (EBOP) aims to remove about 310 tonnes of nitrogen from Lakes Rotorua and Rotoiti over the next 200 years.
‘While plenty of people have opinions, very few have robust analysis of the options available and their comparative cost, benefit, efficiency and effectiveness,’ says Kataraina Maki of EBOP. ‘Obviously, we need a range of ways to reduce nutrient levels and to be sure that the ones we choose are the best ways.’
Dr Suzie Greenhalgh of Landcare Research undertook a comprehensive review of interventions that could be used to reduce the amount of nitrogen in the lakes: water quality trading, cost sharing, reverse auctions, land stewardship and land retirement.
- Water quality trading or nutrient trading involves a market that trades reductions in nutrients. It is premised on the fact that the costs to reduce nutrient losses differ among individual entities depending on their size, scale, location, management. Trading allows sources with high nutrient reduction costs to purchase reductions from sources that have lower reduction costs. Entities with lower reduction costs are economically able to lower their nutrient discharges beyond regulated or permitted levels enabling them to sell their excess reductions to entities with higher costs.
- Cost share payments typically cover some or all of the start-up and installation costs of implementing a less polluting practice and are used to encourage individual landowners (i.e. nutrient sources) to adopt pollution control practices that require capital investment. Like a subsidy, the cost of a nutrient-reducing management practice is shared between a nutrient source (e.g. landowner) and government.
- Reverse auctions are a mechanism that can be used to cost-effectively allocate funding. They differ from standard auctions in that they have one buyer and many sellers. In reverse auctions, participants have an incentive to reveal the minimum compensation they are willing to accept to adopt or change management practices. Willingness to accept, which only the participant knows, is important information for an administrator of a reverse auction as they want to purchase the most nutrient reductions they can for the available funding. By making selection competitive, the producers have an incentive not to inflate their bid price much beyond the minimum price they are willing to accept as this may lead to their bid being unsuccessful.
- Stewardship approaches such as memorandums of understanding, memorandums of encumbrance or accords are typically agreements between organisations to undertake a set of specified activities. In this case, they will usually involve agreements to change farm management practices.
- Land retirement is where an entire farm or portion of a farm is retired from agricultural use.
Dr Greenhalgh then assessed the strengths and weaknesses of each intervention as well as their impact, reach and cost-effectiveness.
‘We laid out some of the decisions EBOP would have to make in terms of getting things in place or in design of the interventions, as well as outlining some of the compliance issues the council might have to face, the infrastructure they’d need to support the interventions and some of the decisions they’d need to make on an ongoing basis and within any regulatory framework.’
The conclusions were that no single intervention was going to fully solve the problem. Rather, a suite of interventions is likely to be required to achieve the required reduction in nutrients in the lakes.
The information is now being used to educate councillors, staff and stakeholders as EBOP moves to clean up the lakes.
‘I wanted efficient and robust analysis,’ says Kataraina Maki. ‘Landcare Research undertook all that in a robust way and their experience and skills brought it to life.’
Further information:
Suzie Greenhalgh
What’s to blame for sediment generation – big storms or land use change?
Large, powerful, infrequent storms as well as changes in land use are both major drivers altering the rates of sediment generation and delivery into rivers and the ocean.
Debate has raged over which is more damaging, but there have been few studies where the impacts of the two have been compared.
Over the last few years Les Basher of Landcare Research and NIWA colleague Murray Hicks have been monitoring sediment yield at seven sites in the Motueka River as part of Landcare Research’s Integrated Catchment Management (ICM) programme.
‘To measure sediment yield we continuously measured turbidity and took water samples during storms to get a time series of suspended sediment concentration. This was combined with flow measurements to estimate sediment yield for each storm event. Longer term sediment yield was calculated by summing the storm yields,’ says Mr Basher.
At all sites annual yields were dominated by a few large events which carried most of the suspended sediment load. At all sites also there was a very strong relationship between sediment yield and peak flow during each storm.
A significant storm in the headwaters in March 2005 dumped 160 mm of rain in 4 hours causing severe gully and bank erosion. It also increased sediment concentrations and yields by 10–20 times in the affected headwaters while almost 100 km downstream there was still an increase of 2–3 times.
Sediment yields have slowly decreased over the years since that storm – at some sites yields are similar to what they were before the storm while at others they have remained higher.
Harvesting of exotic forest produced a five-fold increase in event sediment yields and they recovered to pre-harvesting levels in under 5 years. However, these sites did not experience any large storms during the measurement period.
Mr Basher says that land use change was an important influence at small catchment scale but the extent of the yield increase, the time to recover, and the total area affected tended to be smaller than the impacts of the large storm in the headwaters.
‘The large storm was a “threshold” event that perturbed the erosion regime and activated sediment sources.
‘This caused subsequent smaller, more common runoff events from these tributaries to carry sediment loads that were over an order of magnitude larger than those events would normally have carried. This effect extended right down the catchment to the coast. Similar results have been found in other catchment studies and have important consequences for calculating long-term sediment yield,’ says Mr Basher.
Further information:
Les Basher
Web: http://icm.landcareresearch.co.nz
Twenty attributes of good water governance
Water governance is one of New Zealand’s most challenging and complex environmental issues. So what does it take to effectively manage our water resources?
Landcare Research Programme Leader, Andrew Fenemor, and counterparts from The Netherlands and Germany have developed a list of 20 attributes for good water governance.
The attributes were derived from questionnaire responses and structured interviews of 56 stakeholders, each involved in one of five South Island Resource Management Act (RMA) catchment management planning and implementation processes: the Waimea Catchment in Tasman; the Awatere Catchment in Marlborough; the Waimakariri Catchment in North Canterbury; the Waitaki Catchment in South Canterbury; and the Pomahaka Catchment in Otago.
Questionnaire results provided a Strengths-Weaknesses-Opportunities-Threats (SWOT) analysis of the likely effectiveness of each of the five water management planning processes achieving their Environmental Results Anticipated (ERAs). Follow-up structured interviews explored stakeholder views about the barriers to achieving ERAs and institutional shifts that could achieve better outcomes through both planning and implementation phases.
Stakeholders were grouped into government, environmental, iwi, water users and instream sectors. Their responses led to the development of a 3-D governance evaluation matrix allowing assessment of the degree of overall satisfaction with each plan and each sector’s degree of satisfaction with the planning process.
Stakeholder observations
These are some specific observations from stakeholder sectors from which the more generic attributes were developed:
- Plan for land and water together at catchment scales; more holistic planning is sought especially by iwi who mostly do not feel well engaged in water management processes.
- Land–water (catchment) management requires not just water body standards and limits, but also direct limits on some land-based activities and uses (‘Emission Limit Values’).
- Planning processes are not keeping up with management needs, especially in addressing water quality decline.
- Stakeholders need confidence in the science upon which plans are based; making science widely available in an understandable and concise form helps engagement.
- Water users need to have formalised involvement in planning and implementation; but engage other stakeholders too, to avoid marginalising other stakeholder values – examples cited were landscape, spiritual and amenity values.
- Better approaches are needed for balancing diverse values in catchment planning.
- Engagement of stakeholders in planning processes needs continuity and focus; fragmentation and long planning processes can erode trust among the parties, while tight time frames can also disenfranchise some stakeholder groups.
- Communication and engagement of water users and key stakeholders in decision-making during low-flow periods creates cohesion and confidence in the water management regime.
- Water users would like consent renewals to be made less bureaucratic.
Conclusions
The 20 Good Governance Attributes for New Zealand water management planning are:
- Determine the actual carrying capacity of water bodies and the desired carrying capacity to meet the present and future needs of the community
- Have good and timely communication between the full range of stakeholders and the regional council at the early stages of planning
- Attune to the whole instead of segment of the whole in catchment management decision making
- Have clearly connected and defined objectives, policies and methods/rules in the plan
- Provide a clear and concise allocation framework through the three principles of sound water management: environmental flows, flow sharing above that bottom line, and allocation caps
- Avoid political bias in environmental decision making
- Consult regularly and have continuous two-way communication with stakeholders during plan process and implementation phases
- Peer review science and share intellectual knowledge
- Use up-to-date science and monitoring in decision making
- Plan for and incorporate transition between planning process phase and implementation phase
- Facilitate buy-in to plan from anyone administering or implementing it
- Foster team approach to water planning and management within councils
- Produce over-arching resource management vision, with generic national priorities on sustainable water management
- Devolve monitoring to stakeholders within a defined management framework to achieve shared goals
- Build in flexibility to the plans and planning processes to respond to new pressures and achieve defined objectives
- Help achieve planning goals through adaptive management
- Monitor effectiveness and efficiency of plans by measuring them against identified values
- Hold regional councils accountable to a higher regulatory authority for their effectiveness and efficiency of plans and implementation
- Ensure water quality targets influence land-based planning
- Spread the burden of water management costs among users
Further information:
Andrew Fenemor
Web: http://icm.landcareresearch.co.nz
Carbon storage
Do exotic species affect carbon storage in forests?
Landcare Research scientists are offering new insights into the complex issue of managing exotic species as well as carbon in New Zealand forests.
There is growing evidence that exotic species can dramatically alter a range of ecosystem processes, both above and below ground, including those that affect carbon sequestration.
Forests are increasingly managed for carbon sequestration, driven by the need to offset carbon dioxide emissions and to mitigate the effects of climate change. Land managers are now considering whether the control of exotic species within those forests is also beneficial to carbon sequestration for emissions trading and other purposes.
Led by Dr Duane Peltzer, researchers have reviewed the role of invaders in forest carbon management and whether we can predict where, and if, they will have effects on carbon stocks. The research was recently published in the scientific journal Global Change Biology, and is based on a review of the science from around the world as well as examples from New Zealand.
Dr Peltzer says data are urgently required to underpin policy development to encourage effective forest management and to provide credibility to the efficacy of exotic species management as an option for offsetting greenhouse gas emissions and trading in carbon credits. As such, three issues require urgent resolution: Do biological invaders affect carbon sequestration either positively or negatively? Can these effects be mitigated through management? Can specific invaders or invaded systems be prioritised for management?
The review is a ‘stocktake’ of research undertaken in various places and has been condensed into plants, decomposers and herbivores. Although researchers and managers have focused on weeds and mammal pests; invaders that are not currently managed such as soil invaders and pathogens can have bigger effects than the invaders currently managed.
Dr Peltzer says little is known about managing invaders or the long-term effects of this. For example, while it is known that exclusion of deer can facilitate the recruitment of palatable tree species over a decade or two, little is known about the longer-term carbon consequences of this management.
‘The assumption that managing pest herbivores increases stocks of carbon is not necessarily correct,’ Dr Peltzer says. ‘In fact, the presence of pests might result in more carbon because the vegetation that is affected by such pests can become dominated by “large, long-lived, unpalatable” tree species.’ For such reasons the Department of Conservation has recently initiated a research programme, Wild Animal Control and Emissions Management.
Furthermore, Dr Peltzer says that to date, most of the management of New Zealand forests has been focused on protecting biodiversity – but management practices will change significantly if land is instead managed for carbon. A key message is that managing forests for biodiversity is entirely different from, and sometimes incongruent with managing for carbon.
Further information:
Duane Peltzer
Soil, water, and carbon trade-offs in New Zealand
Landcare Research is developing models to assess the trade-offs of soil, water, and carbon associated with forestry. Researcher John Dymond explains the issues.
Over the last 150 years following European settlement, much of the original indigenous forest in New Zealand has been converted to pasture. In hill country, where tree roots are important for stabilising slopes, deforestation has led to increased erosion, and consequently increased sedimentation in waterways. This has had detrimental effects on aquatic ecosystems by smothering habitat and significantly reducing the penetration of photosynthetically active light. The recreational values of rivers have reduced, along with their flood capacity.
The remedy for soil erosion in hill country is reforestation and tree planting: reforestation or scrub reversion on steep slopes; and agro-forestry or soil conservation planting on less steep slopes. Tree planting has the additional benefit of sequestering carbon from the atmosphere and mitigating global warming. Indeed afforestation on marginal land may be justified on the basis of carbon sequestration independent of soil erosion mitigation. Soil conservation plantings such as space-planted poplars on slopes or pair-planted poplars in gullies store little carbon per hectare. But forestry, especially if it is permanently maintained, can sink high rates of carbon –up to 10 tonnes/ha annually for Pinus radiata forest.
While soil conservation and carbon sinks may be co-benefits of afforestation, water yield is a trade-off. In New Zealand’s generally temperate climate, forestry produces less runoff than pasture; typically about 30% less. This is due to much larger interception of rainfall and subsequent evaporation. So in catchments of water shortage during summer, reforestation may reduce water yields below critical levels needed to maintain water supply and irrigation.
Landcare Research, in a FRST-funded programme – Ecosystem Services for Multiple Outcomes, is developing models to assess the trade-offs of soil, water, and carbon associated with forestry. From maps of land cover, these models produce maps of water yield, erosion, and carbon sequestration rates at 1:50,000 scale. For example, the figures below show an evaluation of benefit (in dollars) for soil conservation, water yield, and carbon sequestration, of new Pinus radiata afforestation. The separate benefits are brought together by assuming that sediment has an associated cost of $1.50 per cubic metre, water has an irrigation benefit of $1 per cubic metre (where there is demand for irrigation), and that sequestered carbon is worth $20 per tonne.
Green shows areas with positive overall benefit while red shows areas with negative overall benefit, or disbenefit. The figures show that the overall benefit from afforestation is highly variable. In the North Island there are significant positive benefits in Northland, Gisborne – East Coast, coastal Wairarapa and Wellington, Coromandel and coastal Waikato (Fig. 1). In the South Island, only southern Marlborough and some areas in Otago show significant positive benefit, while there are large areas of disbenefit in Canterbury and Otago (Fig. 2). The main lesson learned from this analysis is that afforestation designed for environmental benefits should consider a range of ecosystem services.
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| Figure 1. Annual benefit for soil conservation, carbon sequestration, and water yield of new Pinus radiata afforestation in the North Island. Dark green is greater than $150/ha; light green is between $100 and $150/ha; red is less than negative $150/ha; light red is between negative $100 and negative $50/ha. | Figure 2. Annual benefit for soil conservation, carbon sequestration, and water yield of new Pinus radiata afforestation in the South Island. Dark green is greater than $150/ha; light green is between $100 and $150/ha; red is less than negative $150/ha; light red is between negative $100 and negative $50/ha. |
Further information:
John Dymond
Can we increase carbon storage in agricultural land?
New Zealand is currently investigating opportunities to adopt land management practices that will maintain or, in some cases, possibly increase the carbon stored in agricultural lands, reports Landcare Research soil scientist Dr Carolyn Hedley.
About 75% of land farmed in New Zealand is devoted to pastoral farming so carbon storage incentives need to focus on improving grazing land management. This is a new challenge and focus for soil carbon researchers and farmers. ’Many New Zealand farmers have a well-developed understanding of their soils so are well placed to respond to any suggested mitigation strategies that would help to maintain, or even increase, soil carbon levels on their properties,’ says Dr Hedley.
Soil carbon levels on New Zealand farms are typical high – certainly higher on average than in Australian soils, for example. This is because much of this land is high productivity pasture, under a temperate climate, and originally under forest. In addition New Zealand’s volcanic ash soils are particularly good at stabilising soil organic matter.
Dr Hedley is also co-ordinator for CarbonNet, a national programme that connects up our carbon research community and provides expert knowledge and advice on the role of soil carbon processes and inventories.
’There are big challenges for measuring soil carbon accurately over time, to adequately include, for example, its spatial variability over the size of one farm. Traditional methods of soil sampling, including an estimate of the bulk density of the soil, are very time consuming and expensive.’
Dr Hedley says new geostatistical and software methods are becoming available to explore the spatial relationship of point data across a landscape. The only additional piece of information required is the position – and the easy availability and affordability of accurate GPS systems now makes this easy information to acquire.
An article by Dr Hedley and colleagues in the New Zealand Journal of Agricultural Research, 2009 (see below), reports on the assessment of soil carbon sequestration under land recently converted from plantation forest to pastoral farming.
’In addition new proximal sensing methods are becoming available which speed up the process of soil carbon analysis in the field. These proximal sensing methods are at the development stage; they allow more measurements, but at perhaps less precision than the traditional methods.’
Dr Hedley says an article by Kusumo et al. in the Australian Journal of Soil Research, 2009, describes a proximal Vis-NIR sensing method for field analysis of soil carbon.
The newly formed New Zealand Agricultural Greenhouse Gas Research Centre will undertake research into methane, nitrous oxide and soil carbon, looking for methods to reduce methane and nitrous oxide emissions and to stabilise soil organic matter levels in our agricultural soils. CarbonNet, which works alongside the Centre, is exploring how soil carbon is stored in soils, and how quickly this can change.
Soil carbon researchers are also looking at the effects of changing land use, management, and climate on soil organic matter levels; as well as developing improved methods to verify the amounts, and rates of change, of soil carbon in New Zealand soils.
References
Hedley CB, Kusumo, BH, Hedley MJ, Tuohy M, Hawke M 2009. Soil C and N sequestration and fertility development under land recently converted from plantation forest to pastoral farming. New Zealand Journal of Agricultural Research 52: 443–453.
Kusumo BH, Hedley CB, Hedley MJ, Hueni A, Tuohy M, Arnold G 2008. The use of diffuse reflectance spectroscopy for in situ carbon and nitrogen analysis of pastoral soils. Australian Journal of Soil Research 46: 113.
Further information:
Carolyn Hedley
Web: www.CarbonNet.co.nz
Native forest management
Restoring the large podocarps
Landcare Research is aiding the Tuawhenua Trust in its efforts to get podocarp trees (miro, rimu, kahikatea, tōtara, mataī) in its forests restored to the number present before logging last century.
Researcher Fiona Carswell says that since it’s not possible to plant all the lands in the right mix of these species and then tend them to maturity, we need to work with nature as much as possible.
In this article Fiona summarises what we already know about podocarp regeneration in these types of forests and at which points in the life cycle we can try and tip the balance in favour of these forest giants.
Natural dynamics of tawa–podocarp forests
In most North Island tawā–podocarp forests tawa has been increasing in dominance during the last 100 years. This seems to be a natural process, in part because tawa can regenerate in its own shade. Very large disturbances (like volcanic eruptions) favour the podocarps, particularly the species that seem to need more light, e.g. tōtara, kahikatea, rimu. However, parent trees can live for a long time (hundreds of years) and seedlings of many species can survive in the shade of other trees for at least 80 years. This means that podocarps can hang on until the conditions are right for their growth.
Effects of logging on Tuawhenua forests
Given the right conditions logging can favour rimu regeneration. However, on Tuawhenua lands extensive logging of the podocarps appears to have helped tawa to become even more dominant (Figs 1 & 2).
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| Figure 1. Change in forest type between 1960 and 1980. The map above left was drawn in 1960 (McKelvey 1973) and the map above right was drawn in 1980 (Nicholls 1990). Logging operations occurred during the 1960s and 1970s. The most striking difference is the reduction in tawa–podocarp forest (yellow area) and its replacement with tawa forest (orange area). | |
The most important effect of logging has been the widespread removal of very large podocarp trees. Very large trees occupy lots of trunk area and the amount of this removed can be seen in Fig. 2 where we show the change in trunk area with logging. All podocarp trunk areas decreased while tawa trunk area increased.
How much regeneration is there now in logged forests?
We estimate that before logging there were about 18 stems of tall podocarp trees (across all the species) per hectare. Using average death rates for these trees and current numbers of seedlings we estimate that there are not enough seedlings to regenerate the forest to the previous number of tall trees.
Podocarp seedlings in the logged forest will have mostly come from parent trees that have since been removed by logging. Also, any gaps created by logging are about to disappear so it’s unclear whether existing seedlings/saplings in logged forest will make it to the canopy, particularly for rimu. We expect there to be a lot more tawa trees in this type of forest than podocarp trees but we still think that the current number of podocarp seedlings is very low.
Therefore some planting of seedlings would be useful, particularly if these could grow into trees that would provide more seed for the rest of the Tuawhenua lands. Given that rimu naturally regenerates before some of the other species and that stock is more readily available, we think planting rimu would be a good start to restoration. Under optimal conditions rimu can seed in as little as 20 years. Rimu is eaten by kererū and once it is well established miro also comes in and acts as a kererū food source. However, the Trust is also transplanting seedlings of the other podocarp species from areas of the forest where there are too many to all survive.
Where do podocarp seedlings regenerate naturally?
Naturally regenerating podocarp seedlings are more commonly found near ridges, away from gullies and tree ferns (Carswell et al. 2007). The soils where they regenerate are often quite high in nitrogen but low in soil phosphorus. Rimu grows best when it has a lot of light overhead but is still sheltered from the side. It can grow faster than tawa in the light and it seems to naturally regenerate after disturbance before miro, which might only reach its peak abundance at least 200 years after rimu! Increasing the amount of nutrients available to seedlings benefits rimu and miro but also tawa.
Transplanting seedlings
Evidence from Forest Service trials suggests that planting larger seedlings gives better survival and growth rates. Larger seedlings (> 1 m) have been reported to grow up to three times faster than smaller plants (Steward & Pardy 1990). Given the current scarcity of nursery-raised seedlings, an acceptable compromise is probably seedlings of c. 50 cm. However, since the Tuawhenua Trust has opted for transplanting (instead of nursery-raised seedlings) to retain whakapapa links, we suggest that seedlings should ideally be < 50 cm in height to maximise chances of survival.
We need to think about the best place to plant rimu seedlings. Ideally it would be a place that was protected from domestic stock, particularly cattle, and accessible by 4WD so that we can transport people and seedlings to the site. We also want the local school to be able to visit the site easily.
We will be looking for lots of ridges to plant seedlings on and we would ideally like the tawa canopy to be naturally open – maybe from snow damage? It would be good to consider also whether a few tawa trees could be removed to create bigger canopy gaps that would give the seedlings the best chance of fast growth while they develop into trees. Data from the Forest Service trials suggest that gaps of 3–4 m in diameter are necessary where the surrounding vegetation is 6 m high and, naturally, gaps should be correspondingly larger where the canopy is higher (Bergin et al. 1988). It also has been suggested that weeding should occur around seedlings periodically to help achieve maximum rates of growth and survival.
We would like to see whether the seedlings grow better under kānuka trees or under tawa trees. Therefore some seedlings will be planted in the tawa forest and some will be planted in the kānuka forest.
We need to provide the right conditions for the fungi that grow in rimu roots and help the tree to extract nutrients from the soil. This can be done by selecting warm sites that are not too acidic and by placing forest soil in planting holes with seedlings.
At the time of planting we might cut a trench around rimu seedlings to reduce tawa root growth near to the seedlings – this would mean more water and nutrients left for the rimu. This seems particularly important for rimu trees growing in the light.
Progress during winter 2009
Last year 400 seedlings (mainly rimu but also kahikatea, tōtara, mataī) were transplanted to three areas deficient in naturally regenerating seedlings. The survival rate has been highest where seedlings were transplanted to areas with existing shelter. Some canopy opening has been initiated. Survival rates are currently being assessed in order to inform 2010 transplanting.
References
Bergin D, Pardy G, Beveridge A 1988. Planting to restore or extend native forest remnants. Tree Grower May 1988: 44–47.
Carswell FE, Richardson SJ, Doherty J, Allen RB, Wiser SK 2007. Where do conifers regenerate after selective harvest? A case study from a New Zealand conifer–angiosperm forest. Forest Ecology and Management 253: 138–147.
McKelvey PJ 1973. The pattern of the Urewera forests. New Zealand Forest Service Technical Paper 59.
Nicholls JL 1990. Urewera. Forest Service Mapping Series 6.
Steward GA, Pardy GF 1990. Performance of rimu planted in gaps after salvage logging, Pureora Forest Park. Forest Research Institute, Forest and Wildland Ecosystems Division, Northern Wildlands Project Record No. 2563.
Further information:
Fiona Carswell