A form diagram to optimise pruning schedules for eucalypt clear-wood production

Branch pruning is necessary to produce high-value wood products from eucalypt plantations. Four requirements of an effective and efficient pruning regime for clear-wood production are to (a) restrict the pruned-stem diameter to a specified maximum, (b) ensure only green branches are pruned, (c) remove a proportion of the green crown that allows for continued competitiveness of the pruned trees and (d) minimise the number of pruning interventions. In this paper, we present a pruning decision support tool that diagrammatically combines results from growing stands and crown reduction trials. Elements depicting the pruning schedule, target maximum pruned diameter (PD_max), lower height of the green crown (GC_LH) and target retained proportion of the green crown (GC_RP) are overlaid onto a set of stem-taper curves. The form diagram was demonstrated using data from two adjacent commercial plantations of Eucalyptus pellita (‘Caravan Hill’ and ‘Fishtail’), established in the same planting season, for solid-wood production in northern Queensland, Australia. We fitted a cubic tree taper model that described 89% of the variation in stem diameter at a given height. PD_max was set at 12 cm and GC_RP was set at 50%. Pruned height was set at 6 m assuming two lifts.

Site differences in E. pellita growth, slenderness and green-crown height resulted in different optimum pruning schedules even on adjacent holdings. Within-stand heterogeneity in slenderness and green-crown height contributed further to the complexity of pruning scheduling. Our results suggest that it would have been necessary to complete the Fishtail site pruning program at the commencement of the second dry season after planting to ensure that the pruned height was always greater than GC_LH. On the other hand, the first pruning lift could be conducted at the Caravan Hill site at the same time that the second lift was being completed at Fishtail. Management options that increase the height growth in the first year, promote live crown retention and increase within-stand homogeneity will improve the effectiveness of fixed-lift pruning for eucalypt clear-wood production.     

Stem biomass estimation based on stem reconstruction from terrestrial laser scanning point clouds

Forest biomass is often difficult to quantify because field measurements are time consuming and require destructive sampling. This study explores the retrieval of stem biomass of individual trees by terrestrial laser scanning (TLS). Destructive sampling was done to collect biomass data from sample trees and used as a dependent variable in a regression analysis. Two biomass estimation models were investigated: one based on diameter at breast height (DBH) and another based on the sum of the stem section volume. Both the DBH and the stem section volume were determined from automatic reconstruction of the stem curves. Two tree species (Scots pine and Norway spruce) were considered together. The quality of the performance of the models was evaluated via a leave-one-out cross-validation strategy using accurate field measurements for 30 trees. The correlation coefficient (r) and root mean square errors (RMSEs) between the predicted and measured stem biomass were used as measures of goodness of model fitting. The model with DBH as the predictor produced an r-value of 0.93 and an RMSE of 21.5%. For the model using the reconstructed stem and correspondingly derived stem volume as the predictor, an r-value of 0.98 and an RMSE of 12.5% were achieved. The results indicated that TLS measurements are capable of assessing stem biomass with high automation and accuracy by reconstructing the stem from TLS point clouds.     

Crown Recovery of Eucalyptus dives Following Wildfire

The restoration of crowns of 5–7 m tall trees of E. dives of coppice origin was studied after a wildfire on October 1, 1971, near Captains Flat, N.S.W. Unburned plants were compared with those which had their crowns completely scorched but not burned and those which had their leaves completely burned off by crown fire. All trees survived. Approximately 50 per cent of the height of crown-burned trees was killed and 30 per cent in the case of crown-scorched trees. While these results were significantly different most measurements of crown recovery were similar for these two classes of fire-affected plants. Leaf weight was restored within 8 months of the fire. The clumped pattern of epicormic shoots emergent along surviving trunks soon after the fire was replaced by that of the normal branching pattern less than three years later.     

A refined method for estimating capsule crops in individual jarrah (Eucalyptus marginata) crowns

An accurate measure of the number of capsules in the crowns of jarrah (Eucalyptus marginata) trees is needed to assess the potential for seedling regeneration prior to silvicultural treatment in jarrah forests. The current method of estimating capsule crops on jarrah trees uses stem diameter and estimates of capsule density in the crown, but has not been fully validated. In this study, we sought to develop an accurate and practical method of assessing capsule crops in the crowns of individual jarrah trees. We did this by measuring a number of tree characteristics prior to felling them. A total of 24 trees were selected, spanning a range of sizes and crown conditions, and the total number of capsules was counted for each tree. Multiple linear regression was used to model capsule number against various combinations of eight different tree/crown variables, with model fit compared using an adjusted coefficient of determination (adjR²). The final model recommended for field use included three easily measured variables (stem diameter, subjective assessment of capsule density, and subjective assessment of capsule clump distribution in the crown) and had a high degree of predictability (adjR² = 0.83), which was the same as that of the full model. This method substantially improved estimates of crown capsule numbers compared with the method currently used (adjR² increased from 0.29 to 0.83), which tended to underestimate canopy capsule numbers.     

Evaluating wood volume estimates derived from Quickbird imagery with GEOBIA for Pinus nigra trees in the Pentalofo forest,northern Greece

The objective of this research was to evaluate wood volume estimates of Pinus nigra trees in forest stands, which were derived utilizing Geographic Object-Based Image Analysis. Information on forest parameters such as wood volume and number of trees is useful for forest management facilitating forest sustainability. Most of the existing approaches used to estimate wood volume of forest trees require field measurements, which are laboursome. In this study, the collected field data were utilized only in order to investigate the results. Wood volume was estimated based on an individual tree crown approach and using monoscopic satellite images in combination with allometric data. The study area is the Pentalofo forest, which is located in Kozani prefecture in western Macedonia, Northern Greece. About 1 plot surface of 0.1143 ha was utilized. During the preprocessing, a pansharpened image was produced from two Quickbird satellite images (one multispectral image of 2.4 m spatial resolution and one panchromatic image of 0.6 m spatial resolution). Bands of this image were utilized single or in combination in order to delineate the tree crowns individually. The allometric equation served in order to calculate the tree Diameter at Breast Height (DBH) utilizing the detected tree crowns. The evaluation was conducted on three levels: (i) number of trees, (ii) DBH class distribution and (iii) wood volume. On the third level, the evaluation procedure was conducted twice; once using field height and once without. The difference between the results and the field data for the wood volume reached a maximum of approximately 30%. The total number of trees was exactly the same as counted in the field and the DBH distribution showed a tendency for the trees to move to a higher DBH class, resulting in an overestimation of the wood volume.     

Fertilising Eucalypts at Plantation Establishment on Farmland in south-west Western Australia

Responses of Eucalyptus species planted on farmland in the south-west of Western Australia to nitrogen (N) and phosphorus (P) fertilisation were investigated over two and three year periods. Factorial combinations of N (0, 6, 17 and 34 g per seedling) and P (0, 5, 12 and 24 g per seedling) in mostly water soluble (quick release) compounds were applied within a month of planting.

On well drained soils growth of E. globulus exceeded that of E sideroxylon and E. microcarpa by a considerable margin. After three years there were significant (p < 0.05) growth responses by E. sideroxylon to N and P and by E. globulus to P only. In contrast, the third species planted in that experiment (E. microcarpa) showed no significant growth response to N or P. The growth response of E. sideroxylon to a combination of the maximum levels of N and P represented improvements (compared to no fertiliser) of 69% in tree height and 265% in crown volume index. For E. globulus the improvements with each level of P > 0 g were consistently around 14% in tree height and 29% in crown volume index. Improvements in basal area and stem volume index increased with each level of P tested from 13% (5 g P) to 42% (24 g P) in the case of basal area and from 40% (5 g P) to 58% (24 g P) in the case of stem volume index. On poorly drained soils the only significant effect of fertilisaer treatment two years after the planting on the species tested (E camaldulensis, E cornuta and E. woollsiana) was that increasing N level increased seedling mortality. Average mortality rate for the three species increased from 20% (0 g N) to 30% (34 g N).

In other experiments, also with three species on both well drained and poorly drained soils, fertiliser rates were kept constant at 18 g P and 8 g P per seedling but the form and timing of fertiliser application was varied. However, it made no significant difference to survival or growth rates of any species whether the fertiliser was applied in granular or tablet form, at planting time or one month after planting.     

Growth and form of provenances of Eucalyptus saligna at Wondo Genet,southern Ethiopia

A trial testing 10 provenances from across the natural range of Eucalyptus saligna and a local land race was established at Wondo Genet, southern Ethiopia. Eight years after planting, survival, tree height, diameter at breast height over bark, stem form, number of forks, height to the first fork, number of branches, branch diameter and branch angle were assessed. Volume per hectare was also calculated. Survival ranged between 36% (a provenance from 87 km north of Windsor, NSW) and 79% (Consuelo Tableland, Queensland), and differences were significant (P < 0.05). Among morphological characteristics, only the number of branches showed significant variation (P < 0.05), with the greatest number (12.4) being recorded for the Bulahdelah, NSW, provenance and the least (8.5) for the Clyde River, NSW, provenance. Major growth and morphological parameters (tree height, diameter, volume and stem form) did not differ significantly. The overall volume production (mean annual increment 26.4 m³ ha^?1) was well above the minimum acceptable growth observed on good sites elsewhere. Differences between provenances were small and mostly not significant, and no pattern of geographic variation was detected. Given the acceptable mean annual increment, those provenances represented by an adequate number of parent trees could be maintained for further selection and breeding, and to maintain genetic diversity of the species in Ethiopia.     

Relationships between longitudinal growth strain and some wood properties in Eucalyptus nitens

The relationships between longitudinal growth strain and wood properties of Eucalyptus nitens were investigated. Sixty-three 10-y-old trees were selected for this study. Longitudinal growth strain, green density, green moisture content, basic density, radial shrinkage, outerwood and corewood densities, volumetric shrinkage and dynamic modulus of elasticity (MOE) at 12% moisture content and length-weighted fibre length were determined. Amongst all the studied wood properties, only shrinkage-related properties were found to have some association with the mean growth strain in trees. The mean growth strain was moderately but significantly related to the volumetric shrinkage of the outerwood, but not to the shrinkage of the corewood. However, the volumetric shrinkage differential (difference between outerwood and corewood shrinkage) was strongly related to the growth strain (r = 0.70), suggesting that the growth stress gradient might be related to variations in shrinkage properties within the stem. The wood of trees with the lowest growth strains had statistically significantly lower volumetric shrinkage, lower outerwood MOE and less collapse than wood of trees with the highest growth strains. The results suggest that E. nitens trees with low strains could exhibit a lower degree of drying defects such as collapse and checking during processing.     

Potential of two tree shelters to aid the early establishment and growth of three Australian tree species on the Darling Downs,south-east Queensland

The ability of the commercial tree shelter Growtube® and a perforated sheet metal shelter (Mauri) to improve the growth and survival of seedlings of Casuarina cristata, Eucalyptus moluccana and Melaleuca linariifolia was tested on the Darling Downs in south-east Queensland. The 0.9 m high tree shelters were removed after 2 years and at this time tree survival was unaffected by shelter type for all 3 species. Over a 44-month period, neither shelter improved the height growth of C. cristata or E. moluccana. Growtubes significantly (P < 0.05) increased the height of M. linariifolia and, at the time of shelter removal, trees in Growtubes were 23% taller than control trees. Differences in height decreased after the Growtubes were removed and 18 months later were no longer significant (P > 0.05). The early deterioration of the growtubes would have decreased their ability to create a beneficial microclimate, leading to the absence of any height increases for C. cristata and E. moluccana and small and non-persistent height increases for M. linariifolia. Thus, Growtubes were considered unsuitable for the environment in which they were tested. The cost of establishing a tree without a tree shelter, with a Mauri tree shelter and with a Growtube tree shelter was estimated to be $1.82, $3.08 and $5.12, respectively. During the first two years, a further $1.79 per tree was spent on materials used to replace damaged Growtubes.     

Growth and form of Eucalyptus nitens progenies in New South Wales,and selection strategies for a seedling seed orchard

Eucalyptus nitens is potentially the most important eucalypt species for plantations in the tablelands regions of New South Wales. However, genetic parameters and data for provenance and progeny performance of the species in this State have previously not been available. A test of 30 open-pollinated families was established near Tumbarumba (NSW) in 1989, and assessed for a number of growth and form traits at age 5 years. Victorian provenance material, including seedling seed orchard progenies, was generally superior to NSW seed sources for growth and form traits but more prone to forking; all provenances included some superior individual families. Estimates of individual heritability were low to moderate (0.14 to 0.44) for seven growth, stem and branch form traits, with low standard errors, and very low for occurrence of forks and ramicorn branches. Genetic correlations among commercially important growth and form traits were generally moderate to high, and favourable. Selection of trees in the test to retain in a theoretical seedling seed orchard, using a multi-trait selection index, resulted in retention of 90 trees over 11 families, with high gains in growth and form (13.2 to 20.7 percent). Alternative selection strategies, retaining 90 trees over 15 families, gave somewhat lower gains in most traits but a more even distribution of trees over the orchard area.     

Establishment and growth of sandalwood (Santalum spicatum) in south-western Australia: the influence of host species

This study examined the performance of sandalwood (Santalum spicatum) parasitising two N₂-fixing woody hosts (Acacia acuminata and Allocasuarina huegeliana) and a non N₂-fixing host (Eucalyptus loxophleba subsp. loxophleba) on farmland at Kwobrup, Western Australia. The host seedlings were planted in 1991, and the S. spicatum were direct seeded at host age five years. Survival and growth of the S. spicatum were assessed at age three years. S. spicatum survival was significantly higher when planted next to A. acuminata (86 %) than A. huegeliana (29 %), and all seedlings next to E. loxophleba subsp. loxophleba died within two years of establishment. Mean height and stem diameter of S. spicatum parasitizing A. acuminata were significantly greater than those parasitising A. huegeliana. The initial presence of S. spicatum did not reduce host survival or growth.

The foliar N and K concentrations, and the K:Ca ratio were significantly higher in S. spicatum parasitising A. acuminata than A. huegeliana. However, the S. spicatum attached to A. huegeliana had significantly higher concentrations of foliar P, Ca and Mg.

The leaf and stem water potentials (Ψ_leaf' Ψ_stem) of S. spicatum trees were the same or significantly lower than their paired hosts, at pre-dawn and midday, in February-March 1999, the stem water potentials of the S. spicatum: A. acuminata pairing were significantly lower than the S. spicatum: A. huegeliana pairing.     

Polynomial taper model for Queensland plantation hoop pine

A stem taper model, involving a high order polynomial developed using plantation hoop pine (Araucaria cunninghamii Ait. ex D. Don) trees grown in Queensland, is presented. The stem profile for each tree was initially modelled using functions of diameter under bark and height, as the dependent and independent variables respectively. Parameter estimates from these individual tree regressions were subsequently modelled, using total height and diameter at breast height under bark (DBHub) as the independent variables. Finally, total height and DBHub were modelled in terms of predominant height' and diameter at breast height over bark (DBHob).

The largest mean error in the estimates of stem diameter predicted using the final model, with predominant height and DBHob as the independent variables, was 0.12 cm. The overall mean relative error in the estimate of volume, based on coefficients modelled using predominant height and DBHob, was 0.20 per cent. Apart from its accuracy, the main advantages of the model include its simplicity and its ability to model the whole tree using a single function.     

Simulation of thinning effects on stand structure using linear co-ordinates

The effects of different types of thinning strategies on distribution of stem diameters in a forest. Initial stem diameter distribution is derived by the reverse Weibull distribution, and then generating linear co-òrdinates that predict the proportion of trees to be thinned from each diameter class. The techniques have been incorporated in a BASIC program, and this model has proved useful in simulating thinning from below, thinning from above and random thinning to any residual stocking and its effect on stand structure and volume outturn. The model can be incorporated with conventional inventory methods and can be used to generate inputs into growth models for predicting the effect of thinning on future growth of the stand.     

Variation in oil content and tree size between six geographically separate Santalum spicatum families,established near Narrogin,Western Australia

Six geographically separate sandalwood (Santalum spicatum) tree families were established together in a trial near Narrogin, Western Australia to compare oil content and tree size variation at ages 10 and 18 years. The trial site contained a total of 300 sandalwood trees with 41–55 trees from each family. All 300 sandalwood trees were measured for tree size: height, stem diameter and bole length. Wood core samples (heartwood + sapwood) were also taken at 300 mm above the ground from 71 to 72 separate trees, at ages 10 and 18 years. Each wood core sample was ground separately and then a sub-sample was analysed for oil concentration, and α- and β-santalol concentration within the oil.

The mean extractable oil concentrations within the sandalwood stems at 300 mm above the ground were significantly greater from the Borden and Dumbleyung families (1.1–1.6%) than the Ravensthorpe family (0.5–0.8%), at both ages 10 and 18 years. However, the oil quality (mean concentration of α- and β-santalol) was not significantly different between the six families at ages 10 or 18 years. Instead, oil quality was highly variable within each family.

Between sandalwood ages 10 and 18 years, the overall mean extractable oil concentration from the six different families increased significantly from 0.8 to 1.3%. During the same time period, mean α-santalol concentration increased significantly from 8.6 to 13.8%, and mean β-santalol concentration also increased significantly from 3.3 to 4.5%.

Mean tree height, stem diameter and bole length varied significantly between the six families at age 18 years. The Borden family appeared to be more tree-like in form, with a significantly longer bole length, than some of the other families which were more shrub-like in appearance.     

Silvicultural treatments and associated growth rates,growth strains and wood properties in 12.5-year-old Eucalyptus grandis

The effect of a number of silvicultural treatments on peripheral longitudinal growth strains and wood properties was examined at breast height (1.3 m) in 12.5-year-old plantation trees of Eucalyptus grandis (Hill) Maiden. These treatments included: untreated control (C); thinning (T); fertiliser and thinning (F); and fertiliser, weeding, insecticide and thinning (A). Strain was measured using electronic strain gauges glued to the outer xylem.

Stem diameter was progressively greater and growth strain lower in treatments C, T, F and A respectively. Compared to treatment C, treatment A increased diameter at breast height by 190% and reduced longitudinal growth strain by 40%. However, within treatments, the level of growth strain was not related to growth rate.

In silviculturally treated and fast grown trees, the reduced longitudinal growth strain gradient, along a radius from pith to outer xylem, would decrease splitting of wood during conversion.

A positive relationship was found between growth strain and basic density within treatment A, the treatment with the fastest rate of growth. No other significant relationships were found between growth strain and basic density, fibre length, vessel diameter or ray width.     

Selection indices for the genetic improvement of Caribbean pine to increase sawn timber production

Four selection indices were developed for Pinus caribaea Morelet var. hondurensis Barrett and Golfari grown in Queensland, in order to maximise the rate of genetic improvement in the volume of sawn timber recovered from 20-year-old trees. The first index placed no restriction on correlated genetic changes in density or spiral grain while the other three restricted changes in either or both of these wood properties to zero. Measurements of diameter at breast height, height and stem straightness made at 11 years were used as the controlling characters. For all indices, genetic responses in sawn-timber production were predicted using both mass selection and combined selection. Genetic gains of up to 18% were predicted, with an associated reduction of 13% in density. Gains in sawn-timber production of 8% were predicted with no decreases in density or spiral grain. Thus, substantial gains in sawn-timber production may only be possible at the expense of density. Other approaches for the development of a suitable selection index to improve sawn-timber production are discussed.     

Competition for nitrogen between trees in a mixed-species plantation in the Solomon Islands

ABSTRACT

As part of an ACIAR project aiming at improving community forestry in Solomon Islands, mixed-species plantations were established to assess the feasibility of inter-planting teak (Tectona grandis L. f.) and flueggea (Flueggea flexuosa Muell. Arg). Flueggea is a native hardwood used for timber and fence construction, and early removal of flueggea from a mixed-species stand could have a similar silvicultural outcome to thinning a single-species stand of teak. Using ¹⁵N-labelled ammonium sulphate, we investigated the competition for nitrogen (N) between the two species. The ¹⁵N-labelled tracer was applied to the soil surface of plots containing pairs of trees, one of each species, in 2-year-old and 4-year-old mixed-species stands, after the pairs of trees were isolated from the rest of the stand by an impermeable membrane. After 12–18 months, the isolated trees were measured and harvested, and each tree component (roots, stem, branch and foliage) was weighed and analysed for total N and ¹⁵N enrichment. There was no significant difference in the amounts of ¹⁵N between teak and flueggea components at either age, suggesting equal uptake of added ¹⁵N-labelled tracer by both species. The ¹⁵N amount was greater in stem followed by root, foliage and branch for teak and branch followed by stem, root and foliage for flueggea. About 42% and 55% of the applied ¹⁵N tracer were recovered in the 2-year and 4-year plots respectively, suggesting that higher uptake occurs with well-established root structure and that N losses decreased following canopy closure. The amount of total nitrogen was not significantly different between teak and flueggea components at age 2 and 4 years, and may indicate equal access to growth resources, and similar allocation. Although teak had significantly greater stem growth (height, basal area and volume) than flueggea in the 4-year plots, ¹⁵N uptake were similar to flueggea, which may mean that competition for growth resources was still minimal or that access to the resources was equal and growth rates differed between species.     

STAND DENSITY AND THE RELATIONSHIP OF CROWN WIDTH TO DIAMETER AND HEIGHT IN EUCALYPTUS OBLIQUA

The concept of stand density is redefined and the requirements of a density measure for even-aged Messmate stands are discussed. Two extremes of density are recognised in the field, represented by open growing trees on one hand and dominant and co-dominant trees growing in a state of intense competition on the other. For the open grown trees, crown width is linearly related to stem diameter, independent of height, but in stands of maximum density mean dominant height is an important additional variable in the relationship. The effect of this three variable relationship is discussed and it is used to develop an index of stand density for the species, independent of age and site quality.     

Species shade tolerance affects tree basal area growth behaviour in two eucalypt species in thinned and unthinned even-aged monoculture

Individual tree and stand basal area growth were studied in a thinning experiment established over two sites in subtropical eastern Australia. The experiment compared the less shade tolerant species Eucalyptus dunnii with the more shade tolerant Corymbia citriodora var. variegata, both grown in plantation monoculture. Growth was compared over a 2½?3 year period that immediately followed thinning at 5½?7½ years of age. Towards the end of the growth period, tree crown depths and leaf mass per unit area were measured at one site. Crown depth and leaf mass per area of C. citriodora were greater than of E. dunnii, characteristics consistent with a more shade tolerant species. Gross stand basal area growth of E. dunnii was faster than that of C. citriodora. Individual-tree basal area growth behaviour was consistent with inter-tree competition involving asymmetric competition for light. Opening the stand by thinning reduced inter-tree competition to near zero. In unthinned control stands, smaller, more shaded trees of C. citriodora were better able to retain their basal area growth rates than those of E. dunnii in the face of competition. In consequence, the more shade tolerant C. citriodora developed a more evenly spread frequency distribution of tree diameters than less shade tolerant E. dunnii. This would have consequences for the assortment of log sizes that would be available ultimately from monocultures of the two species.