Post from Dean Satchell on April 26, 2016 at 11:44AM
Introduction to Continuous Cover Forestry
Monday, April 25, 2016, Eric Cairn's Blog
The Wellington branch intends to run a series of articles and field days on Continuous Cover Forestry. Government policies, particularly in regard to Permanent Forest Sink Initiatives and in the draft National Environmental Standard for Planation Forestry, are starting to recognise that there are alternatives to clear-fell industrial forestry and the benefits of avoiding clear-fell regimes.
Forest owners are under increasing pressure to join forestry certification schemes in order to retain overseas markets. There is a public perception, rightly or wrongly, that large-scale monoculture forestry, along with huge areas of clear fell at harvest, is not ecologically sensitive. A way to improve public opinion and be more ecologically friendly is to follow the principles of Continuous Cover Forestry (CCF).
CCF means greatly reduced coupe size, mixtures of species and age classes and maintaining or creating habitat and species diversity.
CCF may facilitate:
- a change to harvesting methods (reduced use of cable haulers),
- the need for more sophisticated forest management techniques, and
- different regulatory approaches by national and local authorities.
There is no internationally recognised definition of CCF, but in my opinion it covers a wide spectrum of forestry activities: almost anything but large scale clear-fell regimes.
In its simplest form, CCF can be a series of small compartments of single age, single species with a different specie in each compartment. Harvest is by felling a mosaic of small coupes, thus minimising negative effects on soil, water quality and wildlife disruption.
More complex forms of CCF use mixed age and/or mixed species tree regimes. At the extreme , CCF systems resemble natural forest. Harvesting is then small coupe or single tree selection and stand management may take the basal area of various size classes into account and limit the numbers of trees in each size class according to reverse J curves. These complex variants are usually much more complicated to manage than single age and single species stands.
While US and European foresters accept CCF as feasible, most NZ trained foresters reject the notion that CCF is either reasonable or profitable, particularly for Pinus radiata or on steeper sites lacking easy access.
Radiata is seen as a commodity product and profit margins are often small. Large- scale operations seem to be the norm, and the costs of logging small stands could be high due to set-up costs. Consequently radiata does not lend itself to CCF. From a harvest cost point of view, there would be advantage in growing higher value species, allowing a better margin to the grower.
In most countries CCF is built around management of indigenous species. In NZ however there are strong disincentives for cultivating native trees as there is no guarantee of a right to harvest and crop rotation times may be very long. Perhaps growing mixtures of exotic and indigenous species will provide high ecological and recreational values and still prove profitable but as yet there is little hard data to support this idea.
CCF is suited to high value species, which allow low impact harvesting systems and in some cases on-site milling. While operating costs per tonne are higher than with clear-fell, capital equipment costs can be reduced.
Factors affecting stand profitability include growth rates, saw log values, basal area, economies of harvesting, rotation times, labour of planting, silviculture and management, and appropriate markets for the species and grades obtained. It is hoped that the (potential) higher values of alternative species will offset higher extraction costs and slower growth rates but minor species can be very difficult to market.
Growers contemplating CCF also need to understand whether they want a defined rotation / investment time or the opportunity for a steady income stream over a long period while maintaining a high stand volume.
There may be tax implications here as sale of the forest attracts tax liabilities to both seller and buyer on the assessed value of the stand (cost of bush, see Tree Grower Feb 2005, Murray Downs, on NZFFA website). Amenity trees have different tax liabilities. Sole operators and companies are taxed differently.
Strengths and weaknesses
The Classic European/German system of Plenterwald has the philosophy of leaving the best performing trees until last. This could mean that some oaks would grow for hundreds of years before harvest, but ultimately deliver the highest value and fastest increments to stand volumes. Less scrupulous foresters remove the best performing trees (hi-grade) and leave the rubbish for future generations. This practise rapidly degrades the genetic potential as the poorer trees are left to breed when the higher quality trees are cut.
- the balance of a mixed species stand to be altered mid rotation to meet shifting markets
- some very long individual tree rotations to maximise value
- a more balanced forest microclimate that might improve the quality of an emerging crop
- better outcomes for water, soil and ecology
- better outcomes for recreation and amenity
- an uneven height canopy that is said to reduce pressure harmonics and reduces the risk of wind-throw
- profitable management of small scale blocks with dedicated and specialised labour input i.e. farm forestry.
- there is a limited availability of improved genetics of alternative species in NZ
- need for sophisticated knowledge to manage stand volumes according to species and age structure.
- need for care when thinning or harvesting to avoid damaging other crop trees
- coupe size may depend on shade tolerance of the species, and potential for weed infestation
- thinnings and low grade trees possibly not marketable except as firewood or round wood
- mature logs of minor species might be difficult to sell
- limited opportunities for economies of scale in harvesting and marketing
- higher risk of wind-throw or snow damage for tender advance regeneration understorey
- need for good road access and tracking to minimise extraction costs.
In New Zealand we have so much to choose from, but little experience to draw on (except for indigenous forests). But why follow the North American or European recipes when other species might provide a better return for NZ sites?
The key steps are:
- Firstly, decide whether to grow single age stands or mixed age and or mixed species stands.
- Start with pioneer species and plant tender, shade tolerant ones later if required.
- Match your timber species with climate, soils and exposure and mycorrhiza, remembering that eventually the forest will provide shelter for regenerating trees.
Cypresses, Douglas fir, redwoods and cryptomeria are moderately shade tolerant. Stands with these species can have high basal areas. There are probable markets for medium diameter thinnings of these species.
Acacia melanoxylon benefits from competition when young but must be opened up to wide spacing by 10-15 years or else it will lose volume in low value upper branches and growth will slow. Small diameter blackwood (and most small eucalypt) is full of tension and is difficult to saw into straight boards. Thinnings therefore have little value as sawlogs, but if durable species are grown, sawn or round wood may be in demand for vineyard posts. (e.g. some stringybark eucs).
As hardwoods generally need even growth and wide final spacings, consider an understorey of shade tolerant species as an advance regeneration succession crop. There is a lot of light under a eucalypt stand, especially when thinned correctly. Why not under-plant with a succession crop of native trees? Kauri, puriri and totara could do well and be drawn up in light wells. Obviously under-plantings need to be arranged with harvest of large piece size in mind, perhaps strip planted away from harvest lanes.
Hardwoods such as acacia, oaks, elms, ash, walnut and chestnut benefit from a sheltered environment, but would need to be well spaced by mid rotation. These species are suited to a park like environment, or under-grazed with selected livestock.
Poplars could be a very useful nurse crop and are well suited to pastoral systems.
Light-demanding species such as radiata, can still establish in light wells. The growth may not be as fast initially as open grown stock. In the experience of John Wardle, selection harvesting of pine ensures that most stems harvested are at premium quality and the mean annual increment for the whole stand is higher than a conventional stand. (A conventional stand means annual increment is very low when the stand is young. The slow growing understorey trees are like advanced regeneration in a shelter wood system.)
Some species require soil disturbance or “mineral soil” for self-regeneration. Soil disturbance is often a by-product of selective harvesting, but the species ecology needs to be understood for successful self-regeneration. The tradition in NZ is to replant with improved selections of target species.
Later articles will feature case studies from around NZ and perhaps elsewhere. I understand that John Wardle will shortly publish a book on his CCF experience with black beech and radiata pine. Ian Barton, Paul Millen and those managing native forest stands also practise CCF. Ian Barton through Tanes Teee Trust published a booklet on CCF in 2008.
Disclaimer: Personal views expressed in this blog are those of the writers and do not necessarily represent those of the NZ Farm Forestry Association.