Individual tree growth differences in a clonal eucalypt blanking trial at four years

Achieving a well-stocked stand at time of planting is important to compartment productivity and yield in clonal eucalypt stands for pulpwood production.  The window period in which individuals that replace those that died after initial planting (blanks) still contribute meaningfully to final yield is set by the  competition dynamics between individuals within the stand. The longer the period between planting and blanking, the greater the advantage achieved by original plantings in dominating site resources (light, water and nutrients) and suppressing blanks. A blanking trial was established to determine growth differences of blanked and original individuals and productivity per unit area. Factorial combinations of blanking period after planting, mortality pattern and extent of mortality were tested. Analysis of measurements at four years showed that the period before blanking is the only factor that significantly accounts for the variation in plot volume between treatments, although the percent mortality and pattern of mortality by percent mortality together also have influence on plot volume. Late blanking results in a higher proportion of suppressed trees that contribute little to total volume. Asymmetric competition is more pronounced where late blanking is carried out and where mortality is spread, rather than clumped.Southern Forests 2009, 71(2): 95–9

The influence of tree improvement and cultural practices on the productivity of Eucalyptus plantations in temperate South Africa

The South African forestry industry is dependent on a resource of fast-growing, low-cost wood to remain globally competitive. Land availability and the legislative requirements for afforestation in South Africa are limiting factors for future growth and therefore increasing the productivity per unit area of existing land offers the largest potential to  improving forest productivity and reducing the unit cost of wood production. Operational gain integrates all the components of the deployment process that have an influence on final stand yield, and these include tree breeding efficiency, propagation efficiency, plant use efficiency, matching species to sites, stand density and early  growth through cultural practices. The aim of this study was to gain increased understanding of the interactions between intensive levels of silvicultural management and the deployment of improved genotypes of a number of commercialEucalyptus species, across a range of sites, with varying levels of productivity. To demonstrate the influence of factors associated with productivity gains, a series of five trials were established, on five different sites, within the warm and cool temperate regions of KwaZulu-Natal. At each site and for each factor, a treatment that would exhibit superior productivity was deliberately chosen over a second treatment representing inferior but not uncommon operational practice. The four main factors tested at each site were species (recommended relative to an alternative choice), genetic level (unimproved relative to some level of improvement), planting density (recommended 1 667 stems ha–1 relative to a suboptimal 1 111 stems ha–1), and silvicultural intensity (combination of fertiliser, water and optimum weeding termed ‘high’, relative to a suboptimal level ’low’). Significant productivity improvements at approximately five years (mid-rotation) were demonstrated for the main factors across site productivities and species. Silvicultural treatments contribute slightly more to productivity improvements than tree improvement and species choice. In this trial series, achieving high stocking and fertilising with adequate weed control influenced Eucalyptus productivity to a greater degree than deploying improved genetic material and matching the correct species to the site. The influence of genetics and species has increased over the past three years. In general, interactions between the main factors remain absent, highlighting the additive nature of productivity  improvements for each of the main factors. Southern Forests 2009, 71(2): 85–9

Physiological traits of Acacia concurrens and Eucalyptus crebra with respect to radical site preparation practices in a revegetation trial, south east Queensland, Australia

Hosseini Bai, S ORCiD: 0000-0001-8646-6423Purpose: To successfully establish revegetation, there is a need for weed control. Herbicide application and top soil removal (scalping) may be used to suppress weeds. However, scalping alters soil water and nitrogen availability which in turn may affect plant physiology and performance during the early phase of establishment. Materials and methods: A field trial was established in south east Queensland, Australia, to examine weed control methods, including herbicide application and scalping. Plant survival, mean periodic height gain, specific leaf area and leaf-level physiological traits were measured for Acacia concurrens Pedley and Eucalyptus crebra F. Muell. for 17 months following tree establishment. Results and discussion: Plant survival and growth of A. concurrens were superior in the scalped area compared to the herbicide area, whereas neither survival nor growth of E. crebra was influenced by weed control methods. In general, there were no or little effect of site preparation practices on carbon and nitrogen isotope composition, specific leaf area, photosynthesis, maximum photosynthesis and instantaneous water-use efficiency. Photosynthetic capacity was not influenced by site preparation practices as reflected through the maximum rate of carboxylation and maximum rate of electron transport. Conclusions: Despite altering soil nutrient availability in the scalped areas and high weed coverage in the herbicide areas, there was no substantial alteration in plant physiology for both species. E. crebra was less affected by either low nutrient availability in the scalped areas or high weed coverage in the herbicide areas compared to A. concurrens. Therefore, E. crebra could be considered as a valuable species to revegetate degraded lands. © 2014 Springer-Verlag Berlin Heidelberg

Leptin: a review of its peripheral actions and interactions

Following the discovery of leptin in 1994, the scientific and clinical communities have held great hope that manipulation of the leptin axis may lead to the successful treatment of obesity. This hope is not yet dashed; however the role of the leptin axis is now being shown to be ever more complex than was first envisaged. It is now well established that leptin interacts with pathways in the central nervous system and through direct peripheral mechanisms. In this review, we consider the tissues in which leptin is synthesized and the mechanisms which mediate leptin synthesis, the structure of leptin and the knowledge gained from cloning leptin genes in aiding our understanding of the role of leptin in the periphery. The discoveries of expression of leptin receptor isotypes in a wide range of tissues in the body have encouraged investigation of leptin interactions in the periphery. Many of these interactions appear to be direct, however many are also centrally mediated. Discovery of the relative importance of the centrally mediated and peripheral interactions of leptin under different physiological states and the variations between species is beginning to show the complexity of the leptin axis. Leptin appears to have a range of roles as a growth factor in a range of cell types: as be a mediator of energy expenditure; as a permissive factor for puberty; as a signal of metabolic status and modulation between the foetus and the maternal metabolism; and perhaps importantly in all of these interactions, to also interact with other hormonal mediators and regulators of energy status and metabolism such as insulin, glucagon, the insulin-like growth factors, growth hormone and glucocorticoids. Surely, more interactions are yet to be discovered. Leptin appears to act as an endocrine and a paracrine factor and perhaps also as an autocrine factor. Although the complexity of the leptin axis indicates that it is unlikely that effective treatments for obesity will be simply derived, our improving knowledge and understanding of these complex interactions may point the way to the underlying physiology which predisposes some individuals to apparently unregulated weight gain