Report: Trees for steep slopes
Sustainable Forest Solutions
Reviewed by Mike Marden, July 2018.
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Please note that the web report is regularly updated whereas the pdf download above is dated July 2018.
|Species rating *|
|Early growth rate||4|
|Root decay rate||8|
In a nutshellA hardy pioneer conifer well suited to exposed hill country with lower fertility and poor soils. Growth rates might be adequate for productive plantations. Requires management in the establishment period but high initial stockings may offer selection for straight trees and seedlings grow sufficiently fast to potentially prevent erosion within eight years from planting. Well suited to continuous cover forestry.
Totara is a native conifer and member of the podocarp family, with two species growing into large trees, Podocarpus totara and P. hallii. These species naturally hybridise (Bergin, 2003), with P. hallii being predominant in Southland and Westland. Unlike other New Zealand podocarps, totara is a light-demanding pioneer species and is relatively fast growing (Moodie et al. 2007).
Totara has an extensive natural distribution range through much of New Zealand's lowland and lower montane forest, to about 600 m elevation in the North Island and 500 m elevation in the South Island, occupying both alluvial plains and hill slopes (Bergin, 2003). Natural totara grows as a canopy emergent tree and can grow very large and live for over 1000 years (Bergin, 2003).
Totara has an extensive lateral root system that often spreads further than the crown, along with abundant obliquely-descending peg roots (Bergin, 2003). Totara can produce new root systems after flooding and roots can develop from the trunk where silt has been deposited (Bergin, 2003). Totara seedlings readily develop a vigorous fibrous root system (Bergin, 2003).
The species tolerates a wide variety of sites (Bergin, 2003). Barton (2006) considered totara to be well suited to drier sites and preferentially colonises steeper slopes and poorer pastures (Moodie et al. 2007). Totara tolerates dry soils and seasonal drought but is intolerant of poorly drained soils (Hinds & Reid as cited in Bergin 2003).
Totara regeneration is common in pastoral hill country in Northland, Waikato, King Country, Horowhenua and Wairarapa in the North Island and Nelson, Kaikoura and in Westland in the South Island (Bergin, 2003). Following forest clearance, second growth totara is a prominent feature of many rural landscapes where it has become established in grassland and reverting scrub (Bergin, 2003). Totara regenerates freely in forest margins, open scrub and grassland (McSweeny as cited in Bergin, 2003). Totara successfully establishes on bare ground on steep slopes, facilitated by vegetation suppression from continuous grazing (Bergin, 2003). Totara can develops as a monoculture where no other species is able to regenerate because of grazing pressure. Because totara successfully germinates in grazed pasture and is unpalatable to stock, this offers the opportunity to integrate the species within a grazed livestock operation (Moodie et al. 2007). Where totara regenerates with manuka and gorse, the totara overtops the manuka or gorse within two or three decades (Bergin, 2003).
Young open grown trees form a dense branchy habit and often have multiple leaders, whereas trees with side shading are usually straight and with single leaders (Bergin, 2003). To improve form, totara can be successfully interplanted within short scrub as planted lines (Bergin, 2003).
As open-grown totara grows, a large crown with multiple leaders develops (Cown et al. 2009). Tree form is strongly influenced by stand density and at a higher stocking trees are straighter and with less branching (Bergin, 2003). Open-grown totara tend to have poor form and good diameter growth, whereas within highly stocked stands form is good but diameter growth poor (Moodie et al. 2007). Research has shown that by progressively thinning highly stocked stands, growth rates can be dramatically improved (Moodie et al. 2007). Such active management could utilise different levels of intervention depending on diameter growth required. At age 40 average diameter is 35 cm at a stocking of 400 stems/ha, 20 cm at 1000 stems/ha and 15 cm at 2000 stems/ha, but at a high stocking average diameter will be 30 cm at 100 years (Bergin, 2003). Thus without intervention a wood resource still develops, but more slowly than if progressive thinning is practiced, although dominant trees within the stand are likely to have reached millable size while suppressed trees are failing (Bergin, 2003).
Totara is amenable to tending and responds to nutrition (Bergin, 2003). Although the effects of tree stocking on form and branching have not been subject to any detailed analysis, available information suggests that a high initial stocking in plantations is necessary for good form (Bergin, 2003). Totara planted at stockings of 2000 stems per hectare have performed very well with good form, but for improved diameter growth require subsequent thinning operations (Moodie et al. 2007). Canopy closure can be expected in about eight years for lowland North Island sites established at 2 m x 2 m stockings (Bergin, 2003). Interplanting with faster growing and lower cost species such as manuka would give side shading for improved form along with lower costs and faster site occupancy (Bergin, 2003).
Totara is intolerant of overtopping and severe weed competition, especially weeds that collapse on top of the tree and smother it, such as blackberry and bracken. Overtopping should be managed for up to five years on sites where this occurs. Once trees are two metres high they resist such competition (Bergin, 2003).
Growth rates for planted totara vary according to site conditions but can achieve 2 m in five years and an average diameter of 55 cm in seventy-five years (Bergin, 2003). On average annual diameter increments of 6 mm can be expected and up to 10 mm on fertile sites with corresponding height increments of 55cm (Bergin, 2003). Poor sites may achieve less than one third of the growth rates of good sites (Bergin, 2003). Volumes of 470 m3/ha might be achieved at age sixty years, considerably less than can be expected for Douglas fir at over 1000 m3/ha or cypress at 900 m3/ha (Bergin, 2003).
Totara can be both form pruned and lift pruned for improved production of clearwood (Bergin, 2003).
Planted totara are exempt from the conditions of the Forests Act and can be harvested without constraint (Moodie et al. 2007). When harvested, planted totara are subject to the Forest Growers Levy (Forest Growers Levy Trust, 2017). The Forests Act applies to the milling of all naturally regenerated totara including farm-totara (i.e.trees that were not planted). Although no specific provisions exist under the act for such highly modified second-growth forests, the standards provisions (Sustainable Management Permits & Plans) can be applied. This requires harvests from the natural resource to be undertaken on a sustainable basis.
Totara seedlings can be produced in large numbers and at reasonable cost, either as bare-rooted or containerised stock (Bergin, 2003). Seed should be sourced from local trees (Bergin, 2003). Well produced bare rooted seedlings have a compact fibrous root system and are well suited to late winter planting in cooler regions or autumn planting where winter frosts are not severe (Bergin & Pardy as cited in Bergin 2003). Containerised stock has more flexibility in terms of planting season (Bergin, 2003).
Tree height, diameter growth and stem form vary with seed provenance. A breeding programme could improve the genetic quality of seedlings for plantation forestry by selecting for improved stem form, growth rate and less branchiness (Bergin, 2003). Totara can also be propagated from cuttings and although this might offer an opportunity to produce elite trees with improved form and growth rates in shorter time periods than a breeding programme, the effects of parent tree age on clonal planting stock has not yet been determined (Bergin, 2003).
Establishment of slow growing native tree species is not supported by conventional economic analysis based on financial value alone (Horgan as cited in Bergin et al. 2003). However, economic value improves when non-market benefits are included, such as improved property values resulting from aesthetic improvements that native forest cover offers, particularly on less productive erodible hillsides where runoff water quality and soil stability are also improved, along with improved biodiversity and habitat. (Bergin, 2003).
The significant scale of the existing naturally regenerated totara resource and the sustainability requirements of the Forests Act, address the common problems of sufficient commercial scale and continuity of supply, that beset most alternative plantation species. This means that any planted stands will have the advantage of complementing a larger existing supply source. Initiatives started by the Northland Totara Working Group, continue efforts to facilitate the development a new regional timber industry based on sustainably managed totara.
Longer-term management options that retain non-market benefits and values include selection management and single-tree harvesting (Bergin, 2003). Selective harvesting systems are well suited to managing totara, provided the light-demanding nature of the species is catered for in such practices (Bergin, 2003).
Totara is the most susceptible native podocarp to defoliation by insects. Native insects such as stick insects, scale and cicadas can damage totara trees, with leafroller damaging terminal shoots and affecting tree form (Bergin, 2003). At altitudes above 500 m in the central North Island growth flushes in seedlings can be damaged by early and late frosts (Beveridge, as cited in Bergin, 2003).
Totara is moderately resistant to browsing by cattle, less so by sheep and is susceptible to possum browsing when trees are flushing (Bergin, 2003).
Totara heartwood is a dull pinkish-red to pinkish-brown colour and the sapwood a pale brownish white. Heartwood is very durable and sapwood is reported as "moderately durable in ground contact" (Anon, 1984). Level of durability for sapwood has not been verified for farm-totara in exterior above-ground applications such as cladding but anecdotes suggest the sapwood has some natural durability.
Totara timber is relatively light, straight grained and soft and has a very even texture and excellent stability (Anon, 1984). The timber is of medium strength but with a rather low shock resistance (Anon, 1984).
Totara machines well and is easily brought to a smooth finish (Bergin, 2003). Totara is renowned as an excellent joinery timber, with good screw and nail holding capacity and resistance to denting (Anon, 1984).
Totara sapwood is resistant to attack by Anobium borer (Hinds and Reid as cited in Bergin, 2003). Although the sapwood can be treated with CCA preservatives for in-ground or outdoor use, it is moderately resistant to pressure treatment (Clifton, as cited in Bergin, 2003).
Totara is suitable for interior and exterior joinery, door frames, window sashes, boat building, furniture and carving (Anon, 1984) and totara wood is in demand for cultural use by Maori (Bergin, 2003).
Trees from old-growth forests have a very narrow band of sapwood whereas second growth trees less than 100 years old have a high proportion of sapwood (Bergin & Pardy as cited in Bergin, 2003). Timber from naturally regenerated totara trees between 50 and 120 years old has not been widely used historically, but it is considered to be an excellent native softwood timber (Quinlan & Bergin, 2012). This 'farm-totara', like old-growth totara, is easy to mill, dry, work and finish, and is considered to be suitable for all interior uses, particularly feature linings, joinery and furniture (Quinlan & Bergin, 2012). The natural farm-totara resource has to date not received any silvicultural management, however despite this "all grades of totara timber, including the lighter coloured and knotty grades, rated well for appearance and attractiveness" suggesting that farm-totara should be a relatively valuable specialty timber (Quinlan & Bergin, 2012).
Disclaimer: The opinions and information provided in this report have been provided in good faith and on the basis that every endeavour has been made to be accurate and not misleading and to exercise reasonable care, skill and judgement in providing such opinions and information. The Author and NZFFA will not be responsible if information is inaccurate or not up to date, nor will we be responsible if you use or rely on the information in any way.