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 Debate about cypress management

Allan Levett & Don Tantrum
New Zealand Tree Grower February 2005

This article presents a short debate about cypress management with contributions from Allan Levett and Don Tantrum

Allan Levett’s views

Silviculture
The cypresses at Tinui Forest Park, Wairarapa, have been pruned early and often. After one year they were form pruned, and then at two years, when the trees were usually close to two metres tall, pruned to a stem diameter of three to five centimetres.

Subsequent pruning is on annual basis to stem diameters of one to two centimetres more than the year before. Some at the field day considered these practices too severe. Allan’s justification is based on research reported by Patrick Milne at a Cypress Development Group meeting in Wellington October 2001 and reported in the newsletter and elsewhere.

Patrick’s Balclutha pruning trials began on seedlings and cuttings planted in 1995 and pruned to stem diameters of two, three, four and five centimetres in 1999. Tests in 2000 and 2001 showed no significant impact upon height and diameter growth for trees pruned to more than two centimetres.

Patrick recommended beginning pruning at four years. However Tim Rose and Don Tantrum both with North Island experience advise starting earlier– at an approximate height of two metres when secateurs can be used. Tim prunes first to a stem diameter of four to five centimetres, and Don to six centimetres, both adding a centimetre in subsequent lifts so that the final lift to six metres is to a diameter of eight to nine centimetres.

With early pruning the scars heal rapidly. However it is important to avoid tree stress, and the likelihood of canker, such as wind exposure, wet feet and pruning during a drought. Early pruning was possible this year in the Wairarapa because of the unusually wet autumn.

Nurse trees
Pines had been used as nurse trees at Tinui Forest Park, planted one year later between the cypress rows, which were six metres apart. Each species was planted at three metre intervals within the rows. Therefore the stocking rate is 1100 stems per hectare overall, but 550 stems per hectare for the cypresses. After four and five years respectively, the pines are now close to the height of the cypresses.

There are several reasons for nurse trees. Cypresses benefit from the competition, protection and shading resulting in improved form, easier branching and better health during the first few years. There is a big saving in costs. A pine seedling costs at least a quarter of the cost of a cypress seedling and eight to ten times less than a cypress clone.

If the final stocking is to be 300 to 350 stems per hectare, there is scope for thinning out the least desirable cypress trees at the appropriate time and allowance is made for losses of one sort or another. On the other hand, at 550 stems per hectare there are fewer cypresses to choose from when selecting the final crop trees.

Don Tantrum’s views

Site selection is important, good drainage and shelter are necessary for a successful crop. If the site is not naturally sheltered, use of other trees can be successful. Good site selection will benefit tree health and ease of management.

Temperature is one of the key risk factors for canker, so macrocarpa can be quite suitable for southern slopes.

Select suitable species for site. For example in bad canker areas plant lusitanica, in marginal canker areas, canker resistant macrocarpa.

Tree management
If you get the site and selection right, management will be easier. You should plant at three to four metre spacing. Start pruning whenever you like, and for each metre of pruned height you need 25 mm of stem diameter. So you should prune to two metres for 50 mm stem diameter, and to six metres for 150 mm stem diameter. It is best to prune little and often to avoid tree stress, and only prune crop trees.

The number of crop trees is determined by crop rotation length and whether or not you carry out a production thin. For a 20-year rotation you need 500 stems per hectare and for a 50-year rotation 200 stems per hectare.

Some foresters have success with nurse trees but I have not. You should progressively thin before the cull trees start to affect the growth of crop trees. If you do not thin, then you are wasting your time pruning.
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