Farm Forestry New Zealand

Quick species guides for trees on farms

Howard Moore, New Zealand Tree Grower February 2021.

The information comes from many sources, mostly Scion and NZ Forest Service bulletins and work carried out by NZFFA members and other organisations. The idea is to present in an accessible and standardised way, basic information that is already known and tested. Although we know much more about radiata than cryptomeria, the profiles we have created are about the same length and cover the same information.

For detail, each profile links to all of the best references on the NZFFA website be they reports, videos or Tree Grower articles. There are also some external links, for example to the specialty timbers website, the Emissions Trading Scheme and organisations such as Tane’s Tree Trust, the NZ Redwood Company and Poplar and Willow.

A main feature of the guides is site selection. We have assumed that anyone wanting to grow trees will have a site in mind and be looking for a species. Dean Satchell has spent some time developing a web tool which will help by standardising site factors such as wind, rain, soil and altitude. By choosing any particular combination of these you will find a menu of species suited to those conditions. The menu then links to the species profiles. The main headings used in each profile are −

• General species description
• Site requirements − preparation, planting and spacing
• Establishment and maintenance − releasing, grazing and browsing, pests and diseases
• Management and silviculture − pruning, thinning, when to harvest
• Timber utilisation − markets and demand
• Growth, yield, economics and carbon − carbon sequestration rate and relevant look-up tables, timber return on investment where known
• Further reading and contacts.

The profiles are now on the NZFFA website and we have run some tests to make sure that people unfamiliar with the website can easily find and use them. The aim of the exercise is to make the information accessible. As an example of the writing style, here are some extracts from the profile we have prepared on redwoods.

Species guide 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, which means the cut stump produces new shoots, 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 in height. It prefers altitudes of less than 500 metres and dislikes persistent or salt-laden winds.

Site requirements

Altitude Moderate altitude, low altitude

Rainfall High rainfall, moderately high rainfall, moderately low rainfall

Soil depth Deep, moderate depth

Soil drainage Free draining, moderately free draining, moderately poor draining

Temperature Warm, moderate, cold

Wind Moderate wind

Site preparation and planting

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 do not support weed growth.

Spacing

The natural form of redwood is narrow and conical, therefore high initial stocking is not necessary. If planting at 833 stems a hectare, plant at four metre by three metre spacings or use alternating rows of seedlings and clones six metres apart with trees planted every two metres in the rows. This will allow thinning out of either row in the future. A more sparse planting of 625 stems a hectare at four metre by four metre spacings using elite, fine branching clones will reduce the need for later thinning.

Grazing and browsing

Redwood is not very palatable to stock and deer, but the trees must be fenced 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 damage the 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.

Timber utilisation

Redwood timber 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 once dry it is brittle but very stable. The sapwood is almost white and is perishable, but can be treated with light oil solvent preservatives 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 per cent 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.

Growth, yield, economics and carbon

A growth model has been developed for redwood which 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 as 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 cubic metres a hectare a year.

Carbon sequestration rate

If the land is registered under the Emissions Trading

Scheme and the trees are planted to comply − at least one hectare, with tree crown cover of more than 30 per cent 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, can be downloaded from the Ministry for Primary Industries’ website.

Redwood is an exotic softwood and the tables suggest 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 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 therefore 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, internal rates of return may be of the order of nine per cent a year, assuming Californian prices converted back to New Zealand dollars and including direct costs, overheads and management fees but ignoring land costs.

Further reading and contacts

The Sequoia Action Group may put you in touch with growers in your area. The Redwood handbook can be downloaded as an authoritative reference. The NZ Redwood Company operates redwood plantations and offers good information. Scion has a bulletin on growing redwood, The redwoods: FRI Bulletin 124, Pt 13.

As well as providing useful, accessible information for land owners new to growing trees, these species guides are an opportunity for us to improve the NZFFA website. Collectively as members we have accumulated a wealth of information on the website over the years. While most of it is still true because trees do not change that much, fresh research and experience are continually offering new insights and solutions to old problems. Of course, freshwater reforms and climate change throw up new questions to grapple with.

We welcome input from any readers willing to update website information at any level. If you have the time, expertise and inclination I invite you to contact Dean Satchell or myself, and we will turn you loose. Not only would it be helpful and useful, it might be fun.

Howard Moore is a Wellington member of the NZFFA who is often bullied into writing articles by the editor of the Tree Grower.