NZJFS - Volume 42 (2012)

Pseudotsuga menziesii (Mirbel) Franco (Douglas-fir) is a preferred timber species for sites in the South Island of New Zealand above about 500 m elevation where precipitation exceeds 800 mm. However young stands often exhibit leader tip death, leader break and stem distortion that result in poor tree form. These symptoms may be caused by chemical factors such as boron deficiency or by environmental factors such as frost, snow, wind, insects or disease. Trials were installed in two young Douglas-fir stands at Lake Hill in the Rakaia Valley (570 m elevation) and Balmoral Station in the Mackenzie Basin (870 m elevation) to determine if tree form could be improved by applying boron in the form of hydrated sodium calcium borate hydroxide (ulexite). Stem malformation (stem forking or multi-leadering) was 48% and 88% at Lake Hill and Balmoral respectively. Stem malformation was not reduced by boron application at Balmoral, and only reduced at Lake Hill by the highest boron application rate (32 kg B ha^-1), which also greatly reduced tree stem volume growth. These results indicate that stem malformation was not due to boron deficiency. Boron applied at 4 kg ha^-1 significantly increased tree stem growth at Lake Hill, but reduced stem growth at Balmoral, and higher rates reduced stem growth at both sites. Boron rates of 1 - 2 kg ha^-1 may be more appropriate for young Douglas-fir. This study indicates that a foliar boron concentration of 12 mg kg^-1 may be adequate for good form of Douglas-fir, but may not be adequate for optimum growth. It is concluded that further studies are needed to better understand the link between climate and Douglas-fir tree form in montane environments, as well as to better understand relationships between rate of boron application, foliar boron concentration and growth and form of Douglas-fir in different environments.

Resin pockets are a significant source of wood-quality degrade in Pinus radiata D.Don (radiata pine) logs for many forests around New Zealand. Low rainfall and windy conditions coupled with stony soils and poor soil water-holding capacity have been implicated in their occurrence. Resinous defects have little impact on the structural properties of timber and consequently their occurrence may be underestimated in plantations grown for purposes other than appearance grade timber. It has been common in industry trials to describe resin pockets according to three distinct categories; Types 1, 2 and 3. This paper builds on a series of existing studies directed at understanding the physiological causes of resin pocket occurrence and suggests that current distinctions drawn between different types of resin pockets represent a developmental continuum. Specifically, it argues that a morphological continuum exists between what is generally categorised as Type 1, and Types 2 and 3 resin pockets. It is not intended that the proposed gradation replace the current classification of resin pockets. Rather it is suggested that there is a common physiological cause to better focus research directed at managing their occurrence.

The Land-Use, Land-Use Change and Forestry (LULUCF) sector of the Kyoto Protocol requires New Zealand to monitor changes in the country’s carbon stocks, including those within indigenous forests. Podocarpus cunninghamii Colenso was, in pre-human times, a dominant tree species within the forests of the South Island high country. Anthropogenic disturbance, primarily fire, has converted most of these forests to grassland. Despite this mass deforestation, remnant stands of Podocarpus cunninghamii still exist, and may represent important point sinks of carbon. This study provides first estimates of existing above- and below-ground carbon stocks in high country stands of Podocarpus cunninghamii and presents a preliminary model of Podocarpus cunninghamii carbon sequestration rate. Carbon stocks within high country stands of Podocarpus cunninghamii range from 7.3 t ha^-1 in the drylands to 130.1 t ha^-1 in the wetter areas. Estimates based on tree ring widths indicate a high country-wide Podocarpus cunninghamii carbon sequestration rate of 0.1 - 0.5 t ha^-1 yr^-1 for 250 - 1000 stems ha^-1, respectively.

A tree volume equation for New Zealand’s Nothofagus species was validated using sectional measurements from Nothofagus menziesii (Hook f.) Oerst trees at Alton Valley in Southland. Upper stem diameters of 60 trees were measured using a Tele-Relaskop within three plots that had been thinned to stockings of 150, 1500 and 8228 stems ha^-1. Bark thickness measurements were obtained from a range of heights up tree stems. Merchantable under-bark volumes of stems calculated from sectional measurement were compared with merchantable volumes predicted by a model developed by Ellis (1979). The model was found to predict volumes with minimal bias even though errors were kurtotic and a little outside the range predicted. The correlation between predicted and estimated volumes was 0.97.

It can be difficult to provide large numbers of fresh forest insects for use in fumigation experiments. This paper reports on studies aimed at providing large numbers of fresh burnt pine longhorn beetles (Arhopalus ferus Mulsant) (Coleoptera: Cerambycidae). Burnt pine longhorn beetle is one of the most important pests of quarantine concern associated with export of New Zealand radiata (Pinus radiata D.Don) logs, particularly to India, China and other Asian countries.

The timing of the collection of hundreds of adults, obtaining eggs from them and then storing the eggs for use in fumigation trials must be synchronised with the timing of the trial itself. Three separate experiments were conducted to improve rearing and storage of burnt pine longhorn beetles. In the first experiment, burnt pine longhorn beetle eggs were laid by field-collected adults. Larvae were successfully reared on an artificial (huhu) diet at 20 °C ± 1.5 °C and pupated after 216 days (males) and 227 days (females). Adults emerged after a further 2.5 weeks. These adults stayed alive in the laboratory for up to 46 days at 20 °C. In a second experiment field-collected burnt pine longhorn beetle adults of mixed age were stored at 4, 6, 8, 10, 12 and 14 °C for up to 10 weeks. The longest survival time was at 6 °C (50% still alive after 28 days). In a third study we found 12 - 14 °C was the best temperature for storing eggs. The total life times, times to pupation and adult survival times were not significantly different between males and females. Males tended to be more variable than females particularly in the time spent as larvae and as adults.

Spatial maps of density and stiffness patterns within individual trees were developed using two methods: (1) measured wood properties of veneer sheets; and (2) mixed effects models, to test the hypothesis that within-tree patterns could be predicted from easily measurable tree variables (height, taper, breast-height diameter, and acoustic velocity).

Sample trees comprised an assortment of 25 coastal Pacific Northwest Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees grown on three sites under a range of thinning regimes. At harvest, trees were 36 years old on one site, and 45 and 51 on the other two. After felling and crosscutting, bolts were peeled into veneer, labelled, dried, weighed, measured, and non-destructively tested using a Metriguard 2600^TM veneer tester. The labels allowed each sheet to be tracked back to the peeler bolt and consequently to the position within the parent tree from which it came, and the measurements allowed calculation of veneer density and, after application of the fundamental equation for propagation of sound, veneer stiffness.

Maps of each parent tree created from the veneer data clearly demonstrated regions of higher density and stiffness. Furthermore, within each tree, density was approximately normally distributed, while stiffness tended to have moderate negative skew. Maps developed using mixed effects models showed very good correspondence between measured and predicted patterns, particularly for density. Despite differences in age, site and silviculture, results from this study suggest that it is possible to predict within-tree wood properties using easily measurable tree variables.