Ma Hunt

Allometric relationships for Eucalyptus nitens (Deane and Maiden) Maiden plantations

Abstract Allometric relationships between stem, leaf area and crown dimensions were determined for Eucalyptus nitens (Deane and Maiden) Maiden using 81 trees sampled from 13 post-canopy closure sites and 34 trees sampled from 6 pre-canopy closure sites. These sites differed in site quality, stand age, fertiliser treatment, stand density and levels of weed infestation. Overall, tree age ranged from 2 to 13 years, tree height from 1.4 to 26.1 m and diameter at breast height from 0.6 to 38.7 cm. Pre-canopy closure trees exhibited site-specific relationships which were to some extent confounded with tree age. However, post-canopy closure trees had relationships which were independent of site, age and silvicultural treatments. Strong relationships between structural components were found for both stem and crown. Stem diameter at breast height was non-linearly related to tree height and crown length. Stem sapwood area (breast height or crown base) could be predicted from stem cross-sectional area. For post-canopy closure trees, a functional relationship between sapwood area (breast height and crown base) and leaf area was site-independent. The lack of specificity in terms of both site and management techniques enables these relationships to be applied generally to E. nitens plantations in Tasmania.

Dry matter production and allocation in Eucalyptus cloeziana and Eucalyptus argophloia seedlings in response to soil water deficits

Effects of soil water availability on seedling growth, dry matter production and allocation were determined for Gympie (humid coastal) and Hungry Hills (dry inland) provenances of Eucalyptus cloeziana F. Muell. and for E. argophloia Blakely (dry inland) species. Seven-month-old seedlings were subjected to well-watered (100% field capacity, FC), moderate (70% FC) and severe (50% FC) soil water regimes in a glasshouse environment for 14 wk. There were significant differences in seedling growth, biomass production and allocation patterns between species. E. argophloia produced twice as much biomass at 100% FC, and more than three times as much at 70% and 50% FC than did either E. cloeziana provenance. Although the humid provenance of E. cloeziana had a greater leaf area at 100% FC conditions than did the dry provenance, total biomass production did not differ significantly. Both E. cloeziana provenances were highly sensitive to water deficits. E. argophloia allocated 10% more biomass to roots than did E. cloeziana. Allometric analyses indicated that relative biomass allocation patterns were significantly affected by genotype but not by soil water availability. These results have implications for taxon selection for cultivation in humid and subhumid regions.

Effects of naturally regenerated Acacia dealbata on the productivity of a Eucalyptus nitens plantation in Tasmania, Australia

Abstract Twenty-two plots were established in a Eucalyptus nitens plantation and measured over three years to investigate the effects of naturally regenerated Acacia dealbata weeds on productivity. Under favorable moisture conditions, A. dealbata grew at a rate close to (and sometimes exceeding) that of E. nitens , bringing about canopy closure by two years of age where A. dealbata stem densities were high. Competition peaked at age 2–6 years before declining as the A. dealbata canopy was suppressed, in part by intra-specific Acacia competition. E. nitens basal area was a highly significant inverse correlate of A. dealbata stem density from ages 2–8 years. However, a simple correlation between E. nitens and A. dealbata basal areas was significant only in young stands (age 2–4 years). The effects of early-age competition by A. dealbata on E. nitens productivity were substantial, reducing standing volume compared to Acacia -free plots by almost 25% by age eight years. Soil nitrogen status was positively correlated with A. dealbata presence at both ages sampled (four and eight years) and negatively correlated with E. nitens basal area. A. dealbata was, therefore, considered to be a net contributor of nitrogen during this period, but competition for other resources negated any positive effect of this contribution.

Ageing delays the cellular stages of adventitious root formation in pine

Summary Vegetative propagation programs internationally are affected by the significant decline of rooting success as trees mature. This study compared the cellular stages of root formation in stem cuttings from 15-week-old (juvenile) and 9-y-old (mature) stock plants of the slash × Caribbean pine hybrid (Pinus elliottii var. elliottii × P. caribaea var. hondurensis). The cellular stages of root formation were the same in both juvenile and mature cuttings, beginning with cell divisions of the vascular cambium forming callus tissue. Within the callus, tracheids differentiated and elongated to form root primordia. Roots in juvenile cuttings developed faster than those in mature cuttings and the juvenile cuttings had a much higher rooting percent at the end of the study (92% and 26% respectively). Cuttings of the two juvenile genotypes had more primary roots (5.5 and 3.3) than the three mature genotypes (0.96, 0.18 and 0.07). The roots of juvenile cuttings were more evenly distributed around the basal circumference when compared with those on cuttings from the mature genotypes. Further work is needed to improve understanding of physiological changes with maturation so that the rooting success and the speed of development in cuttings from mature stock plants can be optimised, hence improving genetic gain.

Determination of specific leaf area of some commercially useful sub-tropical hardwood species

Summary Variability of specific leaf area (SLA) across taxa, sites and crown zones was determined for four sub-tropical hardwood species, Eucalyptus grandis, E. cloeziana, E. argophloia and Corymbia citriodora ssp. variegata, growing in south-eastern Queensland. Mean SLA values were stable amongst those taxa sampled on dry sites but varied markedly between provenances of E. grandis on a moist site. Mean SLA did not vary significantly with crown zone in any of these four sub-tropical eucalypts, which is in contrast to that observed in temperate species, both in Australia and overseas. A provenance of E. cloeziana from a moist coastal site exhibited the largest SLA of all taxa studied.

Stable states in soil chemistry persist in eucalypt woodland restorations

Aim: To assess whether restoration of dry eucalypt-dominated plant communities on ex-pasture sites is constrained by soil characteristics. Location: Central Tasmania, Australia. Methods: We use nutrient status to test recovery trajectories of soils within eucalypt woodland restorations established on ex-pasture sites. Eucalyptus trees within these sites have been successfully established but understorey plant communities have had negligible recovery. Soils from restoration sites, aged from 3 to 22Â years, were contrasted with those from two reference ecotypes: established pastures and native eucalypt woodlands presumed to be similar to that originally replaced by the pastures. We hypothesized that (a) total soil carbon to nitrogen ratios (C:N) would be substantially higher in forest soils than in pasture soils; (b) soil nutrient levels would be lower in forest sites than within pasture sites; and (c) if restoration soils were recovering they should fit between these continuums according to age of planting. Results: Woodland and pasture reference soils were highly constrained in soil C:N and conformed to expectations. However, ex-pasture restoration sites retained the characteristically low C:N and high nutrient levels of pasture soils, in particular total N. They also failed to demonstrate a transformational effect with age of planting. Conclusions: The results suggest that both restoration interventions and natural processes had not sufficiently disrupted existing below-ground systems within the given time frame. Such an intractable stable state within the soil system highlights the need within restoration practice for an increased emphasis on soil ecological transformation. Improving and implementing practices aimed at driving soil change may assist a timelier reassembly of complex native ecosystems. This study also shows that soil C:N ratios may provide a cheap and simple means of identifying soil constraints on restoration.