Cunninghamia lanceolata (Chinese fir) : a study of its potential as a commercial plantation species in New Zealand
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Cunninghamia lanceolata (Lamb.) Hook. (Chinese fir) is an evergreen conifer occurring naturally in the sub-tropical region of central - southern China. C. lanceolata is considered one of the most important trees in China, in terms of areas of planting, timber production and timber usage; it has been cultivated as a timber species for over 1000 years and as such its silviculture is well developed. The species has not been planted (commercially) much outside China and Taiwan. The aim of this thesis was to provide, by way of physiological and genetic experiments (of seedlings) on a variety of provenances, information on the prospects for growing C. lanceolata as a commercial forest tree species in New Zealand. Additional factors such as growth pattern and habit, wood properties, palatability to opossums, and climate modelling were also examined. Provenance differences, while reported in the literature, were not so apparent in this study. Isozyme analysis of seed from eight of the eleven seedlots used in this study showed low levels of variability both as a species and between provenances, while a nursery trial did not produce any significant differences in terms of second year height growth or bud burst. However, length of growing season as evidenced by date of bud set did show some variation; with bud set being strongly correlated with latitude, mean annual temperature, mean temperature of the coldest month, and temperature sum. Similarly in the requirement of winter chilling in order to promote bud burst a north-south trend was apparent, as with the nursery trial, with northern provenances bursting fewer buds when little or no chilling was received. For the purposes of this study, however, the only observed difference which is important is the degree of bud set at the end of the growing season, with the closely correlated degree of frost damage. Northern provenances which set bud earlier are therefore better suited to New Zealand conditions. Growth of C. lanceolata responded greatly to temperature: Significant differences were seen between low and high day temperatures, with greatest growth at 28 °c. This is closely related to temperatures during its growth period in China; there, rapid growth occurs between June and September when mean monthly temperatures range from about 22 to 30 °C. There are few sites in New Zealand which have mean monthly temperatures this high over summer. Winter frost resistance was found to be adequate for most New Zealand sites and compares favourably with New Zealand podocarps and P. radiata. Hardiness values were -15.5 to -15.9 °C. Conversely however, C. lanceolata was very susceptible to out of season frosts; a heavy frost of -5 °C resulted in 100 % mortality. Lighter frosts in autumn (ca. -0.5 to -3.5 °C) killed growing tips of seedlings that had not set bud. In choosing sites for the species, out of season frosts are likely to be a major limiting factor. Water requirements were high; new leaf growth was almost 50 % higher for unstressed seedlings (100 % field capacity) than for stressed seedlings (30 and 15 % field capacity). Mortality was also greater at the lowest water level although tolerance to low levels can be developed in well established seedlings at the expense of growth. Recovery of stressed seedlings was apparent after two weeks of rewatering to field capacity; however rates of photosynthesis were still significantly lower than those of unstressed seedlings and conversely stomatal resistance was greater. This suggests that long term (morphological) change had occurred in stressed seedlings. The nutrient experiment showed that nutrient deficiencies and poor growth occurred in seedlings grown at low nutrient levels. Greatest growth was found at high levels compared with other tree species, and tissue analysis also revealed comparatively high levels of foliar concentrations. There was evidence of mycorrhizal colonization resulting in greater seedling growth compared to seedlings that were non-mycorrhizal. However the response was less significant than overall nutrient status and was only apparent at high nutrient levels. Thus the species has a requirement for fertile soils and application of fertilisers. Temperature affected photosynthesis more than did light intensity. At 20 °C light saturation was approached at approximately one third of full sunlight (640 µE) while at 28 °C the response curve was still increasing. Light compensation point was low (20 µE) compared to P. radiata (39 µE). Seedling appearance was also greener when grown under 30 % shade cloth as opposed to full sunlight where seedlings appeared yellowed. This and studies on mixed stands and C. lanceolata's ecology suggest that the species prefers weak sunlight or low light intensities. Other experiments examined the growth pattern and habit of C. lanceolata. The species has a definite seasonal pattern of shoot growth; following bud burst in early September growth was typically sigmoid, slowing down and ceasing around April when buds were set. Small sized resting buds were formed over winter; no height growth occurred from May through to August (winter) until early September when buds began to swell and burst again. The growing season in New Zealand was approximately 8 months, the small size of the bud suggested that predetermined growth was only a minor part of the total season's growth and free growth must therefore follow. Estimation of seasonal shoot growth in mature (25 year old) trees indicated that less than half of a season's shoot growth was predetermined. Free growth allows C. lanceolata to maximise potential growing conditions while the predetermined component acts as a buffer against unfavourable years. Seedlings grown under an 8 hour daylength did not show any difference in growth to those under natural summer daylengths, and there was no sign of bud formation: However seedlings under high day (22 and 24 °C) and low night (9 and 7 °C) temperatures, and long (16 hour) photoperiod showed signs of dormancy after one month. Most seedlings had formed terminal resting buds and had adopted a brown winter colouration. Low night temperatures of 9 °C or less were therefore primarily responsible for bud set. C. lanceolata did not exhibit true dormancy in the sense that chilling was required before growth could resume under favourable conditions. However chilling did significantly hasten bud burst. Provenance differences were noticed when no chilling or very light chilling was applied; however after long periods of chilling all provenances burst bud more or less immediately. This suggests that under natural New Zealand conditions rapid bud burst would occur in all provenances. In addition to defining the species' requirements for (successful) growth, the presence of one 58-year-old stand in New Plymouth and two 25-year-old plots in Rotorua enabled a preliminary study on wood properties to be made. Basic densities were lower than much of the native grown (Chinese) C. lanceolata and considerably lower than the range for P. radiata in New Zealand. The low basic density resulted in lower strength values for mechanical properties (bending, compression, shear tests). Drying rates were very similar to P. radiata and air drying or drying under a conventional (high temperature) P. radiata kiln schedule produce very little degrade. The low strength and basic density of the timber makes C. lanceolata less suitable for structural uses compared with P. radiata, and more suited to end uses where strength is not important. Browse damage from opossums was also examined. Pen trials showed that there was a marked preference for P. radiata over C. lanceolata seedlings in the short term. However once P. radiata seedlings were eaten, C. lanceolata seedlings were then completely stripped over two nights. This suggests that damage at establishment may not initially be a problem, but that once opossums are familiar with C. lanceolata as a food source, damage may well increase. Global modelling using the WORLD program developed by Dr Trevor Booth showed a variety of countries as suitable for C. lanceolata, including those where the species has been planted and trialed. New Zealand sites were considered suitable when both uniform and winter rainfall distributions were included as parameters. A more detailed model for New Zealand developed by Dr Neil Mitchell was next used to identify specific areas. Results showed that C. lanceolata was climatically suited to a restricted range of sites, almost exclusively in the North Island. The experimental findings suggest that while New Zealand conditions may not be optimal for growth, the species nevertheless has (limited) prospects for establishment in New Zealand. Provenance differences in growth were not found at the early seedling stage of growth; however selection of provenances in terms of short growing season may be advantageous in reducing early autumn frost damage. The factors most likely to limit growth potential in New Zealand are: 1) Lower temperatures in the growing season. 2) Out of season frosts. 3) Water deficits, especially during summer. 4) Low fertility sites or lack of fertilising. 5) Possible browse damage by opossums. The climate model results agree with the findings from this study's experiments and furthermore, indicate specific locations. Again, however, the identified sites must also be assessed for the limiting factors given above (with the exception of low temperatures during the growing season) and this may further reduce potential sites.