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There are ways the costs of fighting wilding conifers can be mitigated, writes forestry consultant Jim Childerstone.
In response to the problems, and the costs, of wilding conifer control (ODT, 28.12.11) there is considerable scope to mitigate much of these costs with the recovery of saleable wood in the form of saw logs, post timber (roundwood), firewood and the potential income from chipping residue for boiler fuel.
The latter is becoming a serious contender as a source for alternative energy to fossil fuels, a project I had been investigating for much of last year. And there is a huge potential source of biomass, particularly from wilding clearance.
Some Queenstown businesses are looking at this as an alternative to other more expensive heating methods.
Furnace conversions are already taking place in Dunedin and Invercargill, including for schools and community centres.
In 2006 the Queenstown Lakes District Council adopted a commissioned forestry plan by forestry consultant Branislav Zoric, which effectively divided about 650ha of reserves into separate compartments covering the mature mixed-age forested areas. The majority were mostly conifer species, 80% Douglas fir, the rest European larch and sycamore. Not included were remnant colonies of indigenous red and alpine beech, mostly next to the creek catchments.
I was recruited, part time, to assist the implementation of the plan, having issued forestry reports to previous councils in late 1990s while employed by the Crown Forestry Resource Management Group. The object was to select mature trees of good form for log recovery, leaving others to mature. Net returns were targeted to improve the forests, and the recreational activities within, and also to open the canopy and contain outlier regeneration.
This had originally been achieved in 1998 when several hundred tonnes of top-grade Douglas fir log was extracted on the two lower terraces, giving net returns to the council of about $180,000. Later in 2006-07, two limited harvests of about 1.5ha allowed space for establishing Sequoia dendrum seedlings as a buffer to exclude conifer regeneration. The emphasis for the long term was to implement a managed forest on a more commercial basis, utilising proceeds from harvests for improvements and containment.
Since then, emissions trading scheme carbon credits can generate extra income.
A partial clearance of wilding Pinus nigra (Corsican pine) at Closeburn yielded returns of several thousand dollars to the landowner with recovery of mostly post timber. The fallacy that exotic conifer forests will exclude all other growth can be proved that with an open canopy, because of thinning and select harvest, a prolific under-story of mostly Pittosporum, Coprosma, wineberry and broadleaf native species can take over ground cover. Unfortunately, so will Himalayan honeysuckle and broom, but they can easily be controlled with harvest income.
A good example is Dunedin City Forests' stand of 80-year-old Douglas fir at Flagstaff on Three Mile hill.
One of the problems was to limit conifer seedling spread into the native beech and on to alpine shrubbery. Part of my contract was to hand-clear regenerating conifer seedlings on the edges with a chainsaw and loppers. This gave an indication what a gang of volunteers could achieve within "X" number of working hours.
However, in the hard-to-get areas on steep ridges and gullies the answer possibly is aerial spray application, which after several years is likely to leave a skeletal array of dead forests and a considerably increased fire risk.
What of future options?
This is mainly dependent on available funding, as well as on new technology, scientific research and new tools for control.
Considerable research is under way on the use of bioenergy from vegetation.
Contractors now use improved plant and machinery to handle forests on steep, almost inaccessible sites. A percentage of wilding conifer growth could be accessible for commercial recovery of products to mitigate costs. Already this has been achieved with limited logging operations around Closeburn developments. The recovery included post and pole wood, saw logs and firewood.
While there is still a cost for cleaning up residue from landings and cut-over areas, there is potential for chipping into boiler fuel. A variety of plant is now available for processing this material. Owners of commercial forests have been paid royalties of between $15 and $20 for processed post-harvest residue. Depending on harvest methods about 20% of residue remains on landings and skid sites.
Recovery from mixed-age wilding trees can vary between 20% and 50% in firewood, log and roundwood form. The costs of aerial spraying can vary from $650 a hectare to $2700. The newly developed spray mix targets mainly Douglas fir and larch species, but it is not so efficient and more costly to knock out pines, and can take up to three years to have an effect.
Then there is still the problem of dead trees giving an unsightly look to the landscape, as well as increased fire danger.
How to recover this source of potential energy is a work in progress. A professional logging contractor would charge similar prices per hectare for wilding clearance but given incentives would endeavour to recover saleable wood or, where possible, undertake a clearance operation for nil charges. A crucial factor is the follow-up treatment.
We need constant reminding that the landscape surrounding Wakatipu and elsewhere has been consistently modified over the past 150 years. Trees were grown on the Bobs Peak southern face to prevent rock falls, which had been a threat in the early years of settlement.
Also, most of open high country, including the Remarkables, had been grazed over this period.
Saving the native bush and alpine shrubbery will be a constant battle, keeping volunteers engaged for the rest of the millennium - and beyond.
But there is still money in trees. They are a renewable resource and carbon neutral in rotation or when in a continuous state of management.
- Jim Childerstone (Jim's Forest Services) has been working on some of these issues for 30 years.