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Report: Trees for steep slopes

Dean Satchell
Sustainable Forest Solutions
dsatch@gmail.com
www.go-eco.co.nz

Reviewed by Mike Marden, July 2018

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Please note that the web report is continually updated whereas this pdf version is dated July 2018.



Larch


Species rating *
Early growth rate 6
Permanent canopy 6
Root decay rate 5
Productivity 6
Timber value 7
Coppicing 0
Total rating 5.3

In a nutshell

Larch has good timber properties and reasonable growth rates, provided rainfall is sufficient. A well proven healthy species preferring sheltered slopes and clay soils, with similar siting requirements to Douglas fir but potentially more suited to warmer more humid locations. Lower productivity than Douglas fir. Care required in establishment where woody weeds are present. Like Douglas fir, has a high wilding spread potential but not likely to be an issue in North Island hill country with good rainfall. Hybrid larch grows much faster than European larch.

Larix species (larch) are deciduous northern hemisphere subalpine conifers. Both European larch (Larix decidua) and Japanese larch (Larix kaempferi) have been widely planted in New Zealand, with 3400 ha in plantations in 1988 (Miller & Knowles, 1988). Larch has proven to be a long lived species in New Zealand and can grow into large trees (Miller & Knowles, 1988).

European larch was the major species planted in afforestation programmes in New Zealand in the early 20th century, however it fell into disfavour primarily because of radiata pine's superior growth rates and treatability (Miller & Knowles, 1988). Unfortunately, high initial stockings followed by neglect in these early plantings were not a recipe for success and produced "stands of crowded, poorly crowned trees" (Miller & Knowles, 1988). Japanese larch was not planted as extensively, with small-scale plantings made in Canterbury, Nelson and the central North Island in the 1950's (Miller & Knowles, 1988). European larch can have poor stem form (M. Dean, pers. comm).

Management and silviculture

Larch is easy to grow in the nursery and offers good early growth rates of between 0.5 m and 1.0 m per year for the first 5-6 years (Miller & Knowles, 1988).

Although early height growth rates are often impressive, this may not carry through to high volumes in later years compared with Douglas fir (Ledgard, 2007b). This is because larch is both space demanding and light demanding, so should be thinned regularly to ensure the stand does not become overcrowded (Miller & Knowles, 1988). Recommended final crop stocking for larch is 400 stems per hectare (Ledgard, 2007b), which results in production of lower volumes of wood compared with Douglas fir. Wood properties and appearance is similar to Douglas fir, with excellent toughness and stiffness, but because Douglas fir is less light demanding and also more site tolerant it has become the more favoured species in New Zealand for plantations (Ledgard, 2007b).

Thirty year old trees are typically 16-20 m high with 25-30 cm diameters at breast height (Miller & Knowles, 1988). Sixty to eighty year old trees reach 35 m height and 40-50 cm in diameter (Miller & Knowles, 1988). Unfortunately, growth and yield for larch plantations has not been quantified because older stands have consistently been grossly neglected and performance data would be misleading (Miller & Knowles, 1988). However, Birch (as cited in Miller & Knowles, 1988) concluded that "larch grows well in New Zealand" and at Whakarewarewa Forest a 41-year-old, unthinned stand yielded 450m3/ha on clearfelling.

Larch is fairly tolerant of nutrient and moisture deficient slip faces that lack topsoil, and is similar to radiata pine in this respect (R. Appleton, pers. comm).

Fifteen year old hybrid larch production thinned for posts yielded 1762 posts and 1950 stays, amounting to 83 m3 per hectare, leaving a residual volume of 94 m3 per hectare (Miller & Knowles, 1988). The resulting volume growth and production levels for this stand could perhaps be measured if the stand still existed.

Weeds must be managed well, especially overtopping brush weeds such as broom, because larch does not suppress such weeds (Miller & Knowles, 1988).

Production thinning may be possible for roundwood and firewood (Miller & Knowles, 1988). Miller & Knowles (1988) suggested that  initial stocking should be 1250 stems per hectare (4 m x 2 m), reduced to 400 stems/ha once the trees are 8-10 m high, aiming for a final stocking of 200 stems per hectare on a 60-80 year rotation. Sheep and cattle may be grazed in larch once trees are big enough to withstand damage (Miller & Knowles, 1988).

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Siting

Although a tough tree and capable of surviving in a wide range of sites, larch prefers sheltered slopes in higher rainfall areas for good growth and form, primarily because larch flushes early and late frosts can damage spring growth (Ledgard, 2007b).

Larches are deep rooting trees and grow well in deep fertile clay soils, but do not like poor drainage (Miller & Knowles, 1988). Windthrow is uncommon (Miller & Knowles, 1988). European larch can productively grow at moderately high altitudes of up to 900 m, whereas Japanese larch is limited to 600 m (Miller & Knowles, 1988). Larch requires shelter from excessive wind and sufficient spring moisture for growth and although very frost hardy in winter, is very susceptible to frosting in spring at the time the trees flush (Miller & Knowles, 1988).

Provenance trials of both European and Japanese larch showed little variation between provenances of Japanese larch, but with superior provenances of European larch identified (Miller & Knowles, 1988). Japanese larch grew better than European larch from Rotorua to Nelson whereas European larch grew best in the eastern and central regions of the South Island from North Canterbury to Western Otago (Miller & Knowles, 1988). Two hybrid clones, crosses between European and Japanese larch originating from Denmark where artificial hybrids were produced from select quality parents, were included in the New Zealand progeny trials (Miller & Knowles, 1988). These produced straighter trees, superior growth and greater volumes than both pure species at all sites, this superiority being more pronounced in northern sites (Miller & Knowles, 1988).

Hybrid larch progeny has been produced in New Zealand from selected parents, but performance of these was not reported by Millar and Knowles (1988). Growers report excellent growth rates from hybrid larch (G. Baldwin, pers. comm; A Roulston, pers. comm).

Although larch is considered to be a relatively easy rooting conifer species, propagation of clonal hybrids in Europe encountered high production costs combined with plagiotropy and decreasing rooting quality over time. This has been subsequently improved by using only juvenile stock plants and renewing these every few years (Paques, 2013).

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Weed potential

European Larch has been found to spread freely by natural regeneration in some high country locations in the South Island, but spread is uncommon in the North Island (Miller & Knowles, 1988). Japanese larch has spread in the immediate vicinity of parent stands at Hanmer (Miller & Knowles, 1988). Larch has light seed which can be readily blown some distance giving rise to wilding spread (Ledgard, 2007b). In the high country survey from the early 1980s "this species had the highest incidence and distance of spread of all the more common plantation species, contorta and Scots pine not included" (Ledgard, 2007b). Ledgard (2007b) suggested that larch "should not be planted upwind of lightly vegetated or lightly grazed land". Wilding potential is higher for inland drier areas but it may not deserve its reputation as a vigorous spreader, being palatable to grazing animals and susceptible to late spring frosts (N Ledgard, pers. comm).

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Pests and diseases

Larch canker Lachnellula wilkorrunii is a major disease of larch in Europe but is not present in New Zealand (Miller & Knowles, 1988). However, Japanese larch and Japanese larch hybrids have resistance to the disease (Wunder, 1973).

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Timber

Larch wood has excellent stiffness and toughness with a moderately high density of 560 kg/m3 at 12% moisture (Ledgard, 2007b). Strength and stiffness is high and at least as good as Douglas-fir. Larch has been approved as a framing timber since 1975 (Miller & Knowles, 1988).

Larch has a high proportion of heartwood even as relatively young trees. Heartwood from New Zealand material is not durable in ground contact and larch heartwood is resistant to impregnation with preservatives (Miller & Knowles, 1988).

Sawing is straight forward and although care is required in seasoning larch air dries readily (Miller & Knowles, 1988).

Larch is an attractive decorative timber with a prominent grain. Knots are small, numerous and tight, although "the timber has a slight tendency to splinter and 'pick out' at knots during machining" (Miller & Knowles, 1988).

Larch kraft pulps have high tearfactor and reasonable tensile strength so is particularly suitable for packaging papers (Miller & Knowles, 1988).

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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.

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