Redwood - Coast redwood, Sequoia sempervirens
Redwood is a fast-growing giant softwood, native to California and extensively planted in New Zealand. It prefers moist, deep soils and will tolerate some frosts. It coppices, and develops an extensive root system making it suited for erosion control on lower slopes. On good sites it will grow for more than 1,000 years and reach over 100 metres high. It prefers altitudes of less than 500 metres and dislikes persistent or salt-laden winds.
Commercial return: Medium -
RainfallHigh rainfall; Moderately low rainfall;
AltitudeModerate altitude; Low altitude;
Soil drainageFree draining; Moderately free draining;
Soil depthDeep; Moderate depth;
Soil drainageModerately poor draining
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 is available from some commercial nurseries; Price per tree should range from $0.80 - $2.50 for 1-2 year-old contract-grown forestry stock. Clonal redwood stock should be ordered well in advance so supplies can be available for planting.
To get optimal growth in the first year, plant well before spring on sites that are not prone to frost. 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.
Redwood thrives best in sheltered inland sites such as valley floors, gully bottoms and river flats with deep, fertile, moist but reasonably well-drained soils. It prefers relatively high humidity and a reasonably high, well-distributed rainfall. If you are planting in an unreliable rainfall area use wetted water-absorbing gel in the planting holes to ensure they don’t dry out before they establish roots. Young trees are shade tolerant, but for vigorous early growth need good weed control. Spray releasing for the first year or two is recommended and depending on natural fertility of the site may benefit from fertiliser. Young redwoods may be killed by out-of-season frosts.
Redwood may be planted with a nurse crop. Italian alder is suggested as being an excellent companion species that is faster growing at first but slows later. This the redwoods to grow upward with fine branching, but the redwoods eventually overtake the alders and dominate the site, killing the alders.
The natural form of redwood is narrow and conical, thus high initial stockings are not necessary. If planting at 833 stems per ha, plant at 4m x 3m spacings or use alternating rows of seedlings and clones 6 metres apart with trees planted every 2 metres in the rows. This will allow thinning out of either row in the future. A more sparse planting of 625 stems per ha at 4m x 4m spacings using elite, fine branching clones will reduce the need for later thinning.
- Prevent weeds from competing with the Coast redwood seedlings for at least two years after planting.
- Protect seedlings from browsing by stock and wild animals.
Redwood is shade tolerant but establishes much faster with good weed control. Release spray after planting once weeds begin to regrow, then check the trees annually and release spray weeds until the trees are 2 metres high.
Grazing/BrowsingRedwood 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 redwood 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 redwood 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.
Redwood seed has low viability and falls close to the tree, preventing unwanted spread.
Suitability for steep slopes: Redwoods resprout from the stump (coppice) making them suitable for erosion control. However, because redwood likes a reasonable soil depth and shelter, it is not usually suitable for steeper eroding slopes, but is well suited to lower slopes.
Being shade tolerant, redwood 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.
Redwood is good at withstanding flood events and sedimentation below sites where gully erosion is likely, and it can be planted in flood zones to filter debris flows.
Grown for timber, the target is to achieve large pruned butt logs and upper unpruned logs with green or moribund branches less than 50 mm diameter. If regenerating the trees from coppiced stumps, reduce the stems to three per stump and later thin again to one.
Redwood 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 redwood 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 Coast redwood 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 4 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.
Target diameter needs to be fairly large because market demand is for heartwood. This means final crop stocking should not be more than 350 stems per hectare for a rotation length of 35 years.
Redwood is shade tolerant and will survive in very low light but grows faster with space and sunlight. Thin to final crop stocking 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. Stumps will coppice and shoots will survive in the shade of the crop trees until these are harvested. Managing the coppice growth removes the need to replant. If regenerating the trees from coppiced stumps, reduce the stems to three per stump and later thin again to one.
When to harvest
On sheltered fertile sites in New Zealand redwoods can easily reach heights of over 35 m with diameters of over 65 cm at 50 years. They will continue growing vigorously far longer. Yields can be equal to radiata pine, and for practical purposes a rotation length of around 35 years is suggested, or when the trees reach a target diameter of 60 cm at breast height.
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. Locally they sell at similar prices to radiata pine. A handful of mills around the country have developed a small marketplace for redwood timber.
A redwood growth model and volume and taper equations have been developed for redwood. The model predicts basal area and mean top height for a variety of sites around the country. It is described in the Tree Grower article Performance of coast redwood in New Zealand and may be downloaded as an Excel spreadsheet, the Redwood calculator.
On good quality sites growth rates for redwood can equal or better those of radiata pine, with mean annual increments in excess of 30 m3/ha/year.
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 redwood 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 the Field Measurement Approach of the Emissions Trading Scheme (applicable for forests of 100 ha or more) might well give higher figures for redwood grown on productive sites.
Timber return on investment
Studies of the economics of redwood are few and variable. To date very little is understood about the timber grade and hence value recovery from various log types arising from different management regimes. Log quality is a critical factor in returns. For good sites with regular rainfall such as Taranaki and Bay of Plenty, IRRs may be of the order of 9% pa, assuming Californian prices converted back to NZ$ and including direct costs, overheads and management fees (at 15% of costs), but ignoring land costs.