Redwood - Giant sequoia, Sequoiadendron giganteum
Californian giant sequoia are the largest trees in the world, growing for thousands of years to 60 – 90 metres high and several metres through. They tolerate extremely exposed, windy and dry sites and high altitudes with winter snow. Giant sequoia has been grown as an ornamental in New Zealand and large specimens are found in parks throughout the South Island, where they have achieved over 3 metres diameter at 120 years old.
Giant sequoia dislikes humidity and requires a cool climate, so grows well at high altitudes in New Zealand.
Commercial return: Medium
AltitudeHigh altitude; Moderate altitude;
RainfallModerately low rainfall; Low rainfall;
Soil depthDeep; Moderate depth; Shallow;
Soil drainageFree draining; Moderately free draining;
TemperatureCold; Very cold;
WindSalt laden, strong wind; Strong wind; Moderate wind;
Prepare grass sites by spot spraying a one metre circle for each planting site. Use glyphosate herbicide with spray dye a few days before planting as this will not leave chemical residue in the soil. Prepare spots using straight lines and accurate spacings between spots so that trees can be easily found later. Cut down woody weeds and flatten these on the ground so they decay and don't support weed growth.
Container-grown and bare-rooted stock may be available from some commercial nurseries; however the species is not commonly cultivated. Price per tree should range from $2.00 - $3.50 for 1-2 year-old contract-grown forestry stock (2020 prices).
In dry climates plant well before spring. On colder sites plant in late winter; in warmer areas with few frosts, plant in autumn.
Take great care in the handling, transport and storage of seedlings, especially bare-rooted stock which must be kept cool and moist and planted as soon as possible after wrenching. Containerised (plug) stock should also be planted as soon as possible after receiving the plants. Make sure the root plugs are moist by soaking in a water trough.
Plant trees with a slow release fertilizer tablet underneath or put a trowel of high nitrogen fertiliser such as DAP or urea in a spade slit above the seedling.
Do not "slit and stuff" bare-rooted plants. Plant as per these instructions ».
For containerised stock, dig a hole twice the size of the plant container, leaving some soft soil at the bottom. Tease out (straighten and trim) any pot-bound roots before firming the soil around them, ensuring there are no air cavities.
If you are planting in a low rainfall area use wetted water-absorbing gel in the planting holes to ensure they don’t dry out before they establish roots. Giant sequoia will grow well in well drained soils and does not tolerate poor soil drainage. Young trees are reasonably shade tolerant, but prefer full sunlight.
The natural form of redwood is narrow and conical and thus high initial stockings are not necessary. Plant 833 stems per ha at 4m x 3m, allowing for later thinning to around 300 stems per ha of final crop trees.
- Prevent weeds from competing with the Giant sequoia seedlings for at least two years after planting.
- Protect seedlings from browsing by stock and wild animals.
Giant sequoia is a slow starter, and is not shade tolerant. Good weed control is important during establishment. Spray releasing for the first two years is recommended and it will require weed control for at least 5 years.
Release spray after planting to control weed regrowth, then check them annually and spray or clear weeds until the trees are around 3 metres high, when they can generally outgrow anything but climbing plants such as blackberry and ivy (which should be cleared before planting). Avoid spraying the trees.
Giant sequoia is not very palatable to stock and deer, but they must be fenced out while the trees are young. Cattle can also cause bark damage in young stands by rubbing.
Young sequoia seedlings are palatable to hares and rabbits. They will slice off trees near ground level at a 45 degree angle, killing them.
Possums can cause damage to leaders in some locations and if establishing a giant sequoia plantation it is prudent to poison, trap or shoot them.
Pests and diseases
Cicadas can damage leaders and dead branches can offer entry points to borers, which can attack the heartwood.
Suitability for steep slopes: Giant sequoia doesn't resprout from the stump (coppice). However, because giant sequoia grows on skeletal, dry soils and tolerates exposure to strong winds, it is very suitable for steeper eroding slopes in cooler regions of New Zealand.
Being moderately shade tolerant and very windfirm, giant sequoia can be harvested under a mixed-age continuous canopy system (i.e. where individual trees are harvested on reaching a particular size rather than a particular age). When grown for timber the target is to achieve large pruned buttlogs and upper unpruned logs with green or moribund branches less than 50 mm diameter. Because of its narrow conical form and shade tolerance this species is one of the easiest to grow for timber production.
Giant sequoia has good form with few malformations or double leaders. However, when multiple leaders occur resulting from wind or possum damage, these should be reduced to a single leader if it is a crop tree. Malformed trees are usually thinned in favour of well formed crop trees.
To develop quality clearwood giant sequoia requires pruning.
Clearwood pruning: The aim of clearwood pruning is to minimise the defect core and produce wood free of knots. Pruning "lifts" must be regular and undertaken at a frequency that minimises branch size and diameter over stubs (DOS). Ideally, only final crop trees would be clear-pruned. The smaller more horizontal branches on lower stems of Giant sequoia established within a highly-stocked stand (i.e. 1600 stems per hectare or more) will generally self-prune when they are shaded out. Larger, upward pointing branches should be removed as soon as possible as they will reduce height growth and increase defect core diameter.
Clearwood pruning guidelines are available here.
Prune the stem in 3 to 4 lifts (depending on site productivity) to a stem diameter of 12 cm, and to at least 6 metres height. Annual pruning from 6 years old is suggested to minimise knotty core. Epicormic shoots (i.e. budding from thin bark on the stem in response to sunlight) can be a problem in low-stocked stands and need to be removed.
Suitable pruning tools include loppers and a pruning hand-saw, a battery-operated reciprocating saw, or battery-operated loppers. Form pruning can be undertaken by using a pole pruner.
Giant sequoia is shade tolerant and will survive in reasonably low light but grows faster with space and sunlight. Thin from 833 stems per hectare to around 350 a year or two after pruning is completed, or when the crowns begin to compete. Care should be taken to thin trees before lower branches die, to prevent bark-encased ("black") knots from forming, which allow borer entry into the tree and devalue the timber. The target diameter needs to be fairly large because market demand is for heartwood.
When to harvest
On sheltered fertile sites in New Zealand giant sequoia can reach a top height of over 35 m and diameters of over 65 cm at 50 years. They will grow much slower than that on exposed, dry sites, and for practical purposes a rotation length of at least 40 years is suggested, or when the trees reach a target diameter of 60 cm at breast height.
The timber from plantation-grown giant sequoia is very similar to coast redwood, with a slightly coarser texture.
Redwood is valued for its beauty, light weight, and resistance to decay. The wood is soft and straight-grained, easy to work, odour free, non-resinous and free of oily materials. Its lack of resin makes it absorb water and resist fire. It can be readily air-dried with little shrinkage and degrade, and once dry it is brittle, but very stable. The sapwood is almost white and is perishable, but can be treated with LOSP or boron. The deep reddish brown heartwood is moderately durable, and changes to nut brown when exposed to light.
Redwood’s strength and stiffness values are about 70% of those for radiata of equivalent grade. In New Zealand it complies with the building code as an acceptable solution for exterior cladding but not decking or framing. It may be used as weatherboards and as decorative interior panelling, but its low density, low strength and low hardness restrict its applications. End uses are illustrated in the specialty timber group’s page on redwood.
Markets and demand
Most redwood logs exported from New Zealand have been marketed to Asian countries, such as Korea and Taiwan, where they have fetched good prices. However, giant sequoia is not commercially available in New Zealand.
From a slow start, once giant sequoia are fully established their growth rate improves considerably. On good sites with trees over 10 years old height growth can exceed one metre per year, along with diameter growth of over 25 mm per year. Sequoia continue to put on girth even as they age, and South Island trees now mostly aged 50-80 years are almost always healthy and show no sign of slowing diameter growth. As they are largely open grown, height growth seems to slow at 50 metres.
There are no New Zealand growth models for this species.
Practical hints for measuring trees offers some advice on monitoring growth.
Carbon sequestration rate over time, and relevant Look-up Tables
If the land is registered under the Emissions Trading Scheme and the trees are planted so as to comply, i.e. at least one hectare, with tree crown cover of more than 30 percent in each hectare and an average width of tree crown cover of at least 30 metres, then they should earn carbon credits. The relevant look-up tables for determining how quickly they store carbon and earn credits, and guides to how to use the tables, may be downloaded here.
As giant sequoia is an exotic softwood, tables A2.2 and A2.4 apply, suggesting that over its first 30 years it stores carbon roughly half as fast as radiata pine. However as well as being windfirm, fire resistant and disease resistant, over the long term giant sequoia will outgrow anything else. Accordingly it may be an excellent species for carbon sequestration.
Timber return on investment
There is insufficient information available currently to evaluate the potential of giant sequoia for plantation forestry, despite it having potential on sites where traditional species are less suited.