Nigel D. Turvey

Effects of bracken (Pteridium esculentum (forst. f.) cockayne) on eucalypt regeneration in west-central Victoria

Abstract An experiment was conducted in mixed species eucalypt forest in west-central Victoria to quantify the effects of shading and burning on the competitiveness of bracken with eucalypt seedlings for light and soil moisture. The effect of bracken competition on the species composition of eucalypt seedling regeneration was also studied. The influence of leachate from bracken founds on germination of eucalypt seedlings was examined in vitro. Bracken competition reduced the number of seedlings surviving at age 10 months by 50%. Bracken competition was predominantly for light which reduced seedling vigour making them more susceptible to drought, frost, insects and fungi. The number of seedlings which established was inversely related to bracken leaf area index. Bracken competition did not differentially affect Eucalyptus obliqua or Eucalyptus radiata. Allelopathy from leachate collected from bracken fronds did not affect germination of seeds. Soil moisture was not a significant factor in the competition, but summer rainfall was exceptionally high during this study. Burning and absence of shading stimulated the production of bracken fronds and these conditions are likely to extend the area of bracken competition.

Growth of planted pine trees in response to variation in the densities of naturally regenerated acacias

This paper examines the hypothesis that in a pine plantation competition from naturally regenerated acacia trees can be controlled so that the benefits to the pine trees of nitrogen supply from the acacias could outweight their competing effects. Two herbicide experiments in Pinus radiata in eastern Victoria (Experiments A and B) and one in Pinus elliottii in south eastern Queensland (Experiment C) containing a range of densities of acacia stems and pine volume were used to test this hypothesis. In all three experiments no growth benefit to pine was found at any density of acacia stems. Hexazinone weedicide decreased acacia stems to the benefit of pine growth so that pine growth was negatively correlated with the density of acacia stems (Experiment A, r = −0.801; Experiment B, r = −0.712; Experiment C, r = −0.913). Soil nitrogen concentrations examined in one experiment (A) increased in proportion to the number of acacia stems, but no growth response in P. radiata was found. A multiple correlation of acacia stems (x1) and weedicide rates (x2) explained 67% of the variance in soil nitrogen concentrations (y). If the increase in soil nitrogen is attributed to symbiotic N2-fixation, the annual rate of N2-fixation at a stocking of 4000 acacia stems per ha is 32 kg ha−1. The hypothesis was not proven in as much as for the range of species and sites investigated, all denstities of naturally regenerated acacia stems adversely depressed pine volume growth.

Growth at age 30 months of Acacia and Eucalyptus species planted in Imperata grasslands in Kalimantan Selatan, Indonesia.

Abstract The trials tested a range of establishment techniques for Acacia and Eucalyptus species for pulpwood plantations grown in leached and degraded soils under Imperata grassland (alang alang) in South Kalimantan (Kalimantan Selatan). The results reported here are from measurements at age 30 months. Acacia mangium from Wipim (PNG) had the best growth (57 m3 ha−1); this was 70–80% greater than A. mangium from Subanjeriji (Indonesia). Apart from Acacia crassicarpa, other acacias grew less well and produced multiple stems. Hybrids of Eucalyptus grandis × Eucalyptus urophylla grew exceptionally well and produced an average of 37–46 m3 ha−1. E. urophylla from Wetar also produced 29 m3 ha−1. Amongst other Eucalyptus species, fungal infections and insect damage to foliage increased mortality and reduced total volume production. Chemical weed control of Imperata grass was very important for the successful establishment of all species resulting in a doubling of total volume production of A. mangium (from 26 m3 ha−1 without weed control to 51 m3 ha−1 with weed control), and an 11-fold increase in total volume production of E. urophylla (from 1.8 m3 ha−1 without weed control to 21.3 m3 ha−1 with weed control). Cultivation with a large disc plough increased height growth of A. mangium but had no statistically significant effect on total volume production on this clay loam soil. Fertiliser substantially improved growth of A. mangium producing a total volume of 61 m3 ha−1 in response to the highest rate of NPK (180, 78, and 150 kg ha−1 of N, P and K, respectively), compared with 41 m3 ha−1 without fertiliser. There was no response to additional applications of trace element fertiliser to this soil. Slow release fertiliser gave growth responses in A. mangium similar to other fertiliser applied at rates of up to 20 times greater. The enduring and most important treatments with respect to growth of A. mangium in this environment were the selection of Wipim provenance, chemical weed control and NPK fertiliser, each of which contributed between 29 and 38% of total volume production.

Copper deficiency in coniferous trees

Abstract The most common visual sympton of copper deficiency in coniferous trees is permanent bending and twisting of stems and branches; this has been associated with reduced lignification of the wood. Copper deficiency occurs on acid sandy humus podzols and calcareous soils, and can be induced by the application of nitrogen fertiliser. Total Cu content is highest in soils derived from basic and intermediate rocks, and increases with depth in the soil. Availability of Cu is controlled by organic matter, metal oxides, and soil pH. Protein-bound Cu is involved in electron transfer reactions in plants. The roles of cytochrome a-a3 oxidase and plastocyanin are well known, but the activity of Cu metalloenzymes involved in the production of secondary metabolites (lignins and plant hormones) are most likely to indicate Cu stress. Identifying these metalloenzymes in conifer tissue presents very large analytical problems. Available Cu in soils may be estimated by a range of extractants, but more reliable diagnosis of Cu deficiency is from analysis of plant tissue. Concentrations of Cu in foliage reported to be critical for Pinus radiata D. Don range from 1.5 to 5 ppm. In most cases of copper deficiency sensu stricto, symptoms may be alleviated by application of up to 10 kg Cu ha−1, but far larger applications have been required in some instances. There is circumstantial evidence on which to implicate manganese and ions of similar size competing with Cu in both the soil and plant; thus the causes of Cu deficiency symptoms may be far more complex than a single-element syndrome.

Rooting density and tree size of Pinus radiata (D. Don) in response to competition from Eucalyptus obliqua (L'Herit)

Abstract Nine plots were set up in even-aged Pinus radiata plantations invaded by Eucalyptus obliqua to investigate the effect of below-ground competition from E. obliqua on P. radiata. The plots had different densities of E. obliqua. Individual trees in each plot were measured and mapped. Density contour maps of E. obliqua were made to show four different levels in the stands. Samples at three soil depths from each density level were taken to estimate the rooting density of both species. As the rooting density of E. obliqua increased, the rooting density of P. radiata decreased. This happened at all soil depths. The decrease in rooting density was closely related to the decrease in above-ground tree size of P. radiata. The results highlighted the importance of weed control in the early development of P. radiata stands.

Nitrogen fixing plants in forest plantation management

There is a wide range of nitrogen fixing plants that have been used in forestry with the presumed objective of raising soil nitrogen levels and subsequently improving the growth of the non-nitrogen-fixing forest species. The nitrogen fixing plants that have been tried in managed forest systems range from trees to herbs and shrubs which fix nitrogen through root associations with either Rhizo bium strains in the case of legumes,or an actinomycete of the genus Frankia in the case of non legumes.

Nutrient concentrations in foliage, litter and soil in relation to wood production of 7- to 15-year-old Pinus radiata in Victoria, Australia

Summary We report the changes in nutrient concentrations in unthinned stands of Pinus radiala aged 7, 11 and 15 years old planted across 11 soil types. Correlations between nutrients in foliage, litter and soil (0–20 cm and 20–40 cm) indicated that the links between the components increased with stand age for N and P. Litter weight on the forest floor was dependent upon standing wood volume, and the mass of nutrients in the litter, particularly N and Ca, increased concomitantly with wood volume. The litter layer provided a large pool of nutrients which was related to nutrient concentrations in the surface soil. Concentrations of N and P declined in foliage with age concomitantly with an increase in the amounts immobilized in litter. However, wood volume at age 15 years was positively correlated with foliar N and P concentrations, and the rate of decline in foliar N or P was not correlated directly with a decrease in the rate of wood production.

Effects of micronutrients on the growth form of two families of Pinus radiata (D.Don) seedlings

Micro-element deficiencies have been implicated in the development of poor stem form in Pinus radiata plantations. Cu, Mn and B have been implicated in previous studies as influencing tree form and/or the process of lignification in plants. Therefore an experiment was initiated to examine the individual and interactive effects exhibited by these trace elements on stem form and lignification.The investigation showed that Cu deficiency reduced both lignification and stem form in seedlings. Mn, competing with Cu for uptake, enhanced the symptoms of Cu deficiency. Boron addition did not alleviate the expression of deformity or increase levels of lignification. There was a clear family influence on the development of seedling stem form in response to variations in mineral nutrition.

Soil-type yield curves for Pinus radiata in Gippsland, Victoria

Summary Yield curves are presented for Pinus radiata grown on seven soil types in Victoria. The curves were derived from the Mitscherlich growth model through non-linear regression of growth plot data. The use of yield curves to predict yield from silviculturally improved stands is discussed in the light of soil and site factors influencing the shape of the yield curves.

Variations in response to induced stem bending in seedlings of Pinus radiata

SummaryThe occurrence of stem deformation in Pinus radiata plantations has been examined previously in terms of the factors leading to the onset of bending symptoms. In this study the influence of seedling family and nitrogen availability on the ability of seedlings to recover from deformation was investigated under glasshouse conditions. Seedlings from four families ranging from resistant to susceptible to stem deformation were used. Stem deformation was induced by loading stems with a known weight and comparing bending moments and rates of recovery. Significant differences between families were found with more susceptible families exhibiting greater initial magnitudes of stem lean. Similarly these families also exhibited greater rates of apical elongation following bending despite the larger stem leans. This resulted in more exaggerated stem bends as a consequence of the recovery of the lower stem pushing the upper stem away from the vertical. The strength characteristics of the stems could not explain differences between families. Susceptibility to stem deformation was explained more by stem slenderness expressed as stem height to root collar diameter.