Redwoods – an overview
New Zealand Tree Grower February 2007
Anyone who has spent time in the Long Mile Redwood Grove at Rotorua, or among the great cathedrals of redwood trees in California, will have felt the magic of a redwood forest. When redwoods were first introduced into New Zealand in the 19th century among many other exotic species there were high expectations that they would enhance the New Zealand landscape, and provide us with some of the world’s most sought after timber.
The outcome of early plantings, mainly in the central North Island, was disappointing. The giant trees at Whakarewarewa are the remnants of extensive areas of planting in 1901, and even these struggled in their early years, protected by companion planting of larch, until they eventually claimed the site. The reason for the early failures is not clear, but is likely to include poor site selection, weed competition, and perhaps a lack of suitable mycorrhizae.
The outcome of subsequent plantings in the 1920s and 1940s was similar, with patchy areas of survival which contain some very impressive trees. It also became clear that the local timber did not match the quality of the old growth redwood that was being cut at that time in California. As a result, redwoods fell from official favour. Meanwhile farm foresters, an unruly breed who tend to follow their own instincts rather than orthodox opinion, kept the faith and continued to plant redwoods on their own properties. This has resulted in some very fine stands, and clearly demonstrated that with proper attention redwoods will grow very well in New Zealand.
The redwood revivalA renewal of interest in redwoods has been one of the most interesting trends in forest establishment in recent years in New Zealand. The origin of this can be clearly dated to a farm forestry conference at the Branns’ property in the Bay of Plenty in 1995.
A group of over 300 of us sat in the shade of a spectacular stand of redwoods. Bill Libby, who spoke to us, stood without apparent concern in pouring rain, and challenged us to reconsider redwood as an option for planting.
As Professor of Forestry at the University of California he had conducted research on redwoods over many years, and had closely examined forestry in New Zealand. From his observations of farm forestry plantations he was convinced that, with proper management, redwoods should perform very well in New Zealand, and expressed the view that our conditions are probably better suited to growing redwood than anywhere else on earth. Moreover the quality of locally grown redwood is likely to match the second growth timber currently harvested in California, and therefore likely to attract a high price in a captive market where demand exceeds supply. Finally Bill expressed a long held wish – to some day set up a debate, in California, between a group of New Zealand farm foresters supporting radiata pine, and a team of Californian foresters advocating redwoods.
The debate did take place, in 1997, in the local hall of the Big Creek Lumber Company in Arcata in California. Bill orchestrated the event, having softened our team up with great cunning by taking us on a preliminary tour of the pitch canker-infested pines on the Central Coast, followed by a walk through the majestic redwood forests along the river valleys. This had the expected outcome. It is not easy to win a debate when half the team, myself included, change sides at half time and kick the debating equivalent of a home goal.
Setting up a special interest group
In 1999, Bill was visiting New Zealand, and I took him up to my forest block at Pirongia to look at some redwoods. Wade Cornell joined us. We sat down under the trees and discussed a strategy for setting up a farm forestry special interest group for redwoods and giant sequoia. It would be based on the model of the other action groups, but with a difference. We would kick off with a trial involving group members, designed to give some indications of the growth responses to different sites in New Zealand. It would also link together members of the group.
For some years research into redwood in New Zealand had been abandoned due to lack of funding, and the perception that it was a species without much future here. If we were to engage seriously in redwood planting, a number of basic questions regarding establishment and silviculture needed to be answered. This seemed a good opportunity to fill part of the gap. However it would have to be done without research funding.
The Kuser collection
In 1993, Bill Libby had introduced some clonal material from the Kuser collection in California. The parent trees were unexceptional, but covered the main geographical zones occupied by redwood in California. Limited numbers were planted out, and the clonal material stored at low temperature in Fletcher’s tissue culture lab at Te Teko. The people at Trees and Technology generously agreed to bulk up a selection of clones from tissue culture, and make them available for the trial at cost price.
A few months later we tested the water at the NZFFA Conference in New Plymouth. Bill spoke on redwoods, and I raised the matter of the trial. The deal was that the trial would be self-funding. Participants would buy the trees at commercial rates, plant in a fenced enclosure on their own properties, do their own silvicultural work, and follow a planting protocol which Bill had designed. There would be no financial support.
In a response that showed the real strength of New Zealand farm forestry, over 50 members promptly volunteered. Enough material was available for 55 trial packs, and the trees were planted out in 2002. Ian Nicholas is analysing the data, and the results to date will be presented at the conference next April.
We had assumed that this would be the first in a series of small scale trials which we would have to conduct through the redwood group. However events took a new turn. This started when the Americans arrived.
The big players get involvedIn 2000, a group comprising the owners and foresters of the Soper Wheeler Company, the longest established redwood growing company in California, arrived to check the potential for redwood establishment in New Zealand. Again Bill Libby was the catalyst.
Much of their itinerary was arranged by farm forestry members, and several of us travelled round with them. They were clearly impressed by our growth rates, and the quality of locally grown timber. They returned, as the New Zealand Redwood Company, and are establishing substantial plantations here. They have engaged in research programmes, which include growth modelling and silvicultural trials, and have introduced seed orchard and clonal material from California.
Significant plantations are now being established by local growers, and these will increase as seed orchard stock becomes available.
Redwood forestry is on a roll. However, to avoid repeating the mistakes of the past, there are a number of questions that need to be answered. New Zealand researchers are now active, in particular Rob Webster and his group. The key contribution of Wade Cornell should also be acknowledged.
Where do we plant them?
The site requirements for redwoods are well understood. They need a temperate climate, decent soils and regular rainfall. They do not tolerate heavy frosts, salt spray, or strong prevailing winds, although they will withstand occasional gales. Several trials that are under way, including the farm forestry trial, should indicate the best locations.
These are likely to cover widespread areas in the North Island, and more restricted zones in the south. In view of their longevity and root survival after milling, redwoods are likely to be favoured for planting in areas where soil stability is a problem.
How fast do they grow?
Recent growth modelling studies by Rob Webster have shown that growth rates across a range of North Island sites are appreciably faster than in California. A rotation of about 35 years is therefore realistic.
New Zealand grown redwood has slightly lower density than Californian timber. However when tested in the Californian markets this does not seem important, and it makes sense to compensate for our faster growth rates. Density is influenced by genetics as well as by growth rate, and as Wade Cornell has argued, there is a strong case for considering wood quality when selecting clonal material for propagation.
The superb old growth redwood timber which dominated the Californian market for many years is now available in small and diminishing volumes – about 5% of the market.
The second growth timber that has replaced it has been accepted by the consumers, and this is closely matched by New Zealand grown timber.
What are the markets?
New Zealand redwood growers are privileged. Redwood has great appeal in California, strongly supported by sentiment. Demand should remain high, and supply from the local mills will continue to diminish as the conservation estate expands. Internationally there are few countries that can provide the site requirements for redwood.
Currently the market price for redwood timber in California is about twice that for Douglas fir, and well ahead of radiata pine. There should also be opportunities within the local market.
What should we plant?
At present there is a problem of seed supply. Redwoods on good sites are parsimonious in seed production, and there has not been a good seed crop in California for many years. Seeds sourced from trees in New Zealand should be viewed with caution because of the risk of inbreeding – trees grown from seeds from the Long Mile Grove at Rotorua have performed poorly in controlled trials.
Redwoods have considerable genetic variation. Attention to selection should therefore produce substantial gains in productivity.
The current shortage of supply should change within a year or two as seed orchard and clonal material become available.
A number of trials, together with genetic studies under way should indicate the locations in California from which redwood seeds are best suited to New Zealand conditions.
How do we manage them?
Redwoods are intolerant of weed competition, and should be released for two years after planting. Should they be pruned? I am sure they will be pruned, if for no other reason that New Zealand tree growers are compulsive tree pruners, at times taking that obsession to extreme degrees. Redwoods do not get pruned in California. However I think there is a good case for pruning them. There is a market premium for knot free timber, traditionally satisfied by old growth trees. It has been questioned whether this will persist if increased clearwood volumes come on stream. Pruning eliminates any risk of dead knots, which are bad news in the marketplace.
Pruning encourages the formation of epicormic shoots, which can be a problem. The influence of season of pruning on epicormic formation is under trial. The impact of pruning on growth is under study. Initial testing suggests that pruning to a 10 cm stem diameter is safe. Spacing and thinning trials are also under way. A final spacing of four to five metres between trees is likely, but again more work is needed.
The world’s largest tree Sequoiadendron has a patchy distribution along the Sierra Nevada range in Central California. Its timber has traditionally been regarded as inferior to coast redwood – these giant trees tend to shatter on felling – but trials in California have shown very respectable growth rates, and the timber compares very favorably with coast redwood. It deserves to be more widely planted in the South Island. It is highly tolerant of gale force winds, a point worth bearing in mind as we enter a period where extreme weather events will become more common.
Ian Brown is a member of the Waikato branch