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Macrocarpa growing in its natural range with some radiata pine, at Point Lobos south of San Francisco, California.

» Information courtesy of "New Zealand Tree Grower" magazine - May 2002

What's happening with cypresses
at Forest Research

Gerry Vincent, Luis Gea, Jacqui Aimers-Halliday, Charlie Low and other Future Forests staff - Forest Research, Rotorua

Introduction

Cypresses are the most popular alternative conifers to radiata pine and Douglas fir for woodlot establishment throughout New Zealand. Cypresses have desirable wood properties and, with good stand management, will provide a high-value product. It is estimated that the plantation area of cypresses in New Zealand is about 12,000 to 14,000 hectares. The most important species are Cupressus lusitanica (lusitanica) and Cupressus macrocarpa (macrocarpa).

There is a large amount of natural variation in appearance between individual trees of both lusitanica and macrocarpa. With macrocarpa this is somewhat surprising as it has a very limited natural distribution, being found only in two locations on the coast of Carmel Bay, Monterey, California. In contrast, lusitanica is endemic to parts of central and southern Mexico, the highlands of Guatemala, and extends into Honduras.

By the late 1800s, at least 18 different species of Cupressus and Chamaecyparis had been introduced into New Zealand. These were often planted as individuals or in small groups of each species, so creating opportunities for natural hybridisation. Seed was often collected from a limited number of trees, so it is not surprising that some trees within a stand have features atypical of the species.

For many years, seed stands established by the New Zealand Forest Service at Longwood, Ngaumu, Lismore, Mangatu and Waipoua, were the recognised seed sources. Also, hybrids between Chamaecyparis and Cupressus, the better known being the Leyland cypress clones, were introduced into New Zealand between 1952 and 1989.These have been propagated, primarily for the establishment of shelterbelts. More recently, Forest Research took out Plant Variety Rights (PVR) on five clones of macrocarpa and lusitanica selected primarily for a reduced number of branches per metre of stem and tidy stem form. Dollars collected through their sale supports further cypress research. Some of the clones will soon be dropped as better material is identified in field trials.

The relative case of vegetative propagation of most of the cypresses means that selected clones are available from a number of diverse sources. However, very few of these genotypes have been effectively compared in well-designed field trials. The fact that a tree looks good can often be caused more by environment than genetics. The greatest improvement and assurance of consistent performance is achieved by testing a large number of selected individuals in replicated field trials that are specifically designed to identify the genetic effects.

Macrocarpa growing in a natural population at Crockers Grove, Cypress Point, California.

Macrocarpa in Strathallan genetic field trial, age 11.

The genetic improvement of macrocarpa and lusitanica

Breeding programmes for both lusitanica and macrocarpa were initiated in the early 1980s. The objective is to improve growth, form, and resistance to disease while maintaining wood properties at current levels or better. The macrocarpa programme includes both selected trees from within New Zealand and introductions from native stands in California. The lusitanica material came from New Zealand selections and tree improvement programmes in Kenya and Colombia, but to date, much of the genetic variation in natural stands remains unexplored.

A genetic field test of macrocarpa at Strathallan in Southland is currently being used as a source of improved seed. Out of the 150 families originally planted, the best 30 families have been identified for seed collection. Expected gains from using this material are shown in the table. A family in this context is defined as a group of individuals originating from the same parent tree, which has been selected as superior in the breeding programme.

Table 1: Percentage gain of 'top 30' macrocarpa families compared to the Longwood control seedlot.

The six biggest and better-formed trees within each of the best 30 families at Strathallan were also assessed for wood density and heartwood formation at age 10 years from planting. Family averages for extracted wood density ranged between 334 kg/m' and 388 kg/M3 and averaged 361 kg/M3 The amount of heartwood varied from 0% to 80% of the basal area.

Similar to macrocarpa, a genetic field test of lusitanica at Gwavas Forest in Hawkes Bay is being used as a source of improved seed. Out of the 110 families originally planted, the best 32 families have been identified for seed collection. Expected gains from using this material are shown in the table.

Table 2: Average gain of 'top 32' lusitanica families at Gwavas and Whakarewarewa compared to the Waipoua control.

Material of Waipoua seed stand origin is generally slower growing, but has good stem form and straightness. In age 13 trees at Gwavas, the variation in the average extracted wood density for 32 families ranged from 334 kg/m³ to 408 kg/m³. Heartwood was present in over 95% of the trees sampled, ranging from 0% to 27% of the basal area.

Macrocarpa seedlings from controlled crosses in a 2-year-old field trial at Breadalbane, South Otago.

Seed orchards

A seed orchard is a stand of trees managed for early and abundant production of genetically superior seed. Lusitanica and macrocarpa seed orchards have been established with grafts from the best trees in the breeding programmes. Seedlots with improved growth rate, better stem form, increased resistance to canker and superior wood quality will be available in the near future from Proseed. A small percentage of the sales revenue will be channelled into further cypress research.

Vegetative propagation and clonal testing

A series of clonal tests were planted throughout the country between 1991 and 1998.These tests include lusitanica and macrocarpa seedlings, selected clones, and inter-specific and inter-generic cypress hybrids (Leylands) selected from within cypress stands and earlier research trials. Preliminary assessments have been made for growth and form between ages four to seven years from three North Island and two South Island sites. Results indicate that some clones have improved stem form with lighter branching compared to the seedling controls, but all have poorer growth.

This is similar to the experience with other conifers when some physiological ageing is involved. Physiological ageing is the process of change from juvenile to mature state. Results from an assessment at a later date will hopefully tell if the trade-off of lower growth rates, versus lower pruning costs, is acceptable.

Research into the vegetative propagation of macrocarpa and lusitanica was undertaken in the 1990s at the Forest Research nursery in Rotorua. The objectives were the development of a stool-bed system for propagation of superior planting stock, the multiplication of clones and storage of material while the clones were being evaluated in comparative field trials. The effect of physiological age and the maintenance of juvenility in stool-beds over time are important questions. Details of the propagation system developed by Forest Research, plus the phenomena of physiological ageing, and its impact on clonal propagation and clonal forestry, are presented more fully in the accompanying article.

Collection of pollen from macrocarpa seedling.

Control-pollination

Controlled pollination (or controlled crossing) involves transfer of pollen from a selected male parent to receptive flowers of a selected female parent, and it allows for greater genetic improvement. Research into cypress controlled pollination, initiated by Patrick Milne in Rangiora, is being continued at Forest Research in Rotorua and extended into controlled crossing between cypress species.

Control-pollinated seed has been successfully produced using freshly collected pollen, but pollen storage and handling need further research. Individual trees flower at different times and the season can be spread over many months, thus imposing limitations on the possible combinations of parents that can be crossed. An effective system of pollen storage would mean that crosses could be made between the trees with the most desired traits, rather than just those where the timing of pollen dispersal and female flower receptivity coincided.

Species comparisons

Chamaecyparis lawsoniana, Cupressus lusitanica and C. macrocarpa were included in a species trial at Strathallan and Gwavas in 1985 and these were assessed at age 10 years from planting. The average values from this assessment are given in the table.

Table 3: Comparison of species at Strathallan and Gwavas trials.

Straightness 1 crooked, 9 = straight
Branch angle 1 steep, 9 = flat
Canker 1 = none, 6 = dead

Wood density at Gwavas was assessed at age 12 years with the Ch. lawsoniana
averaging 409 kg/m³, C. lusitanica 372 kg/m³, and C. macrocarpa 386 kg/m³.

Clonal trial with mixed cypress species, C. pygmaea is in the foreground.

Other species research

Cupressus pygmaea occurs naturally further north in California than its close associate C. macrocarpa. C. pygmaea was included in trials planted in 1996 and if it is shown to have potential, more material could be introduced.

The growth rate in a very limited planting of C. guadalupensis planted in1986 appears to be significantly slower than C. macrocarpa.

Two small blocks of Chamaecyparis thyoides were planted in the Long Mile species observation area, Rotorua, in 1966. At age 35 years the average diameter was 22 cm. In 2000, material of known parentage of Chamaecyparis obtusa hinoki was established in Rotorua as a genetic resource stand, which could be used as a seed orchard if required in the future.

Three Leyland cypress clones were compared to macrocarpa in a small trial at one site in Westland at age nine years from planting. The 'Naylors Blue' was significantly larger in both height and diameter than 'Haggerston Grey', 'Green Spire' and the macrocarpa comparison. Trial plantings of the Cupressus lusitanica x Chamaecyparis nootkatensis hybrid, Ovens' cypress, were also established in 1996. Early height growth of this shows promise indicating that further hybrid crossing could be worthwhile.

Predicting growth and yield

Growth models are used to predict volume yield by age and assess the impacts of various forest management decisions on yield. Until recently the lack of data, especially older stand data, has prevented fitting of realistic cypress growth models. A stand-level growth model is currently being developed using successive measurements from a national network of 330 permanent sample plots within lusitanica and macrocarpa stands and field trials.

Predictive branch and crown height models interact to predict knot size, quality and location on the stem. When combined with growth model predictions of standing volume, and defect core dimensions, predictions of recoverable volume by log grade are obtained. Data from a study of cypress branching within spacing trials will be used to model branch size and crown height, and to investigate the impact of branching on grade recovery using Forest Research's AUTOSAW sawing simulation software.

Following development and testing, these models will be delivered via Forest Research's forest management software ATLAS. Economic analyses based on yield predictions, costs and returns, could then be carried out to investigate the influence of various stand management decisions on overall profitability of cypress plantation forestry

Future research

There is a real need for designed field trials that effectively compare the performance of the range of cypress selections that are available throughout New Zealand. To ensure that future selected clones are true to type, it is planned to develop DNA fingerprinting, including parental identification of the tested cypress clones. Morphological markers for determining physiological age also need to be identified.

The development of successful techniques for control-pollination will be extended for use on across-species hybrids as these could have potential in increasing the proportion of desirable traits. For example, the best-tested parents from the macrocarpa breeding programme could be crossed with similar material from the lusitanica programme.

Preliminary investigations have begun on the introduction of other cypress species that are not well represented in New Zealand. Chamaecyparis nootkatensis is likely to be the first of these because of its successful use in Leyland cypress clones. A native of North America, the natural range of this species extends from Alaska to northern California. Emphasis will be placed on obtaining seed of the more southern provenances.

It is usually accepted, but not proven, that cypresses have a relatively low variation in wood properties from pith to bark. This implies that useable timber could be milled from relative small diameter trees such as thinnings. Suitable cypress stands for a short-rotation cypress sawing and utilisation study have been identified and a research proposal prepared. As mill studies are a large cost research area, assistance for funding is being sought from industry.

An economic analysis of growth model predictions for seedling and clone yields, planting stock cost and pruning cost data, is required to evaluate the relative profitability of plantations established with cypress seedlings or more expensive clonal material.

The establishment of clonal tests using material from the breeding programme, combined with the development of clonal storage methods while the material is under test, will mean that large gains could be made from the use of tested clones in the future.

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