Growth performance and management of a mixed rainforest tree plantation

Monoculture plantations of Pinus, Eucalyptus and Acacia have been established oil rainforest lands throughout the world. However, this type of reforestation generally supplies low quality timber and contributes to landscape simplification. Alternatives to exotic monoculture plantations are now beginning to gain momentum with farmers and landholders attempting to establish a variety of rainforest trees in small plantations. When compared to the well studied commercial species, knowledge concerning the growth and management of many of these rainforest species is in its infancy. To help expand this limited knowledge base an experimental plantation of 16 rainforest tree species in a randomised design was established near Mt. Mee, in south-eastern Queensland, Australia. Changes in growth, form (based on stem straightness, branch size and branchiness), crown diameters and leaf area of each species were examined over 5 years. Patterns of height growth were also measured monthly for 31 months. Species in this trial could be separated into three groups based on their overall growth after 5 years and their growth patterns. Early successional status, low timber density, high maximum photosynthetic rates and large total leaf areas were generally correlated to rapid height growth. Several species (including Araucaria cunninghamii, Elaeocarpus grandis, Flindersia brayleyana, Grevillea robusta and Khaya nyasica) had above average form and growth, while all species in the trial had considerable potential to have increased productivity through tree selection. As canopy closure occurred at the site between years four and five, growth increments declined. To reduce stand competition a number of different thinning techniques could be employed. However, simple geometric or productivity based thinnings appear to be inappropriate management techniques for this mixed species stand as they would either remove many of the best performing trees or nearly half the species in the trial. Alternatively, a form based thinning would maintain the site's diversity, increase the average form of the plantation and provide some productivity benefits.

The effects of habitat fragmentation due to forestry plantation establishment on the demography and genetic variation of a marsupial carnivore, Antechinus agilis

We conducted a demographic and genetic study to investigate the effects of fragmentation due to the establishment of an exotic softwood plantation on populations of a small marsupial carnivore, the agile antechinus (Antechinus agilis), and the factors influencing the persistence of those populations in the fragmented habitat. The first aspect of the study was a descriptive analysis of patch occupancy and population size, in which we found a patch occupancy rate of 70% among 23 sites in the fragmented habitat compared to 100% among 48 sites with the same habitat characteristics in unfragmented habitat. Mark-recapture analyses yielded most-likely population size estimates of between 3 and 85 among the 16 occupied patches in the fragmented habitat. Hierarchical partitioning and model selection were used to identify geographic and habitat-related characteristics that influence patch occupancy and population size. Patch occupancy was primarily influenced by geographic isolation and habitat quality (vegetation basal area). The variance in population size among occupied sites was influenced primarily by forest type (dominant Eucalyptus species) and, to a lesser extent, by patch area and topographic context (gully sites had larger populations). A comparison of the sex ratios between the samples from the two habitat contexts revealed a significant deficiency of males in the fragmented habitat. We hypothesise that this is due to male-biased dispersal in an environment with increased dispersal-associated mortality. The population size and sex ratio data were incorporated into a simulation study to estimate the proportion of genetic diversity that would have been lost over the known timescale since fragmentation if the patch populations had been totally isolated. The observed difference in genetic diversity (gene diversity and allelic richness at microsatellite and mitochondrial markers) between 16 fragmented and 12 unfragmented sites was extremely low and inconsistent with the isolation of the patch populations. Our results show that although the remnant habitat patches comprise approximately 2% of the study area, they can support non-isolated populations. However, the distribution of agile antechinus populations in the fragmented system is dependent on habitat quality and patch connectivity. (C) 2004 Elsevier Ltd. All rights reserved.

Measurement of glass-rubber transition temperature of skim milk powder by static mechanical test

Stickiness behavior of skim milk powder was investigated based on the mechanical property of the material during the glass-rubber transition. A thermally controlled device was developed for the static mechanical test. This device was attached to a texture analyzer, and skim milk powder, which was used as a model sample, was tested for its glass-rubber transition temperature (Tg-r) using static compression technique (creep test). Changes in compression probe distance as a function of temperature were recorded. Tg-r was determined, in the region where changes in the probe distance were observed, by using linear regression technique. The effect of sample quantity, compression force, and heating rate on the determination of Tg-r was investigated. All these parameters significantly influenced the Tg-r determination (p < 0.05). The Tg-r of skim milk powder measured by this novel technique was found closely correlated to its glass transition temperature (T-g) measured by DSC.

Financial and economic performance of long-rotation hardwood plantation investments in Queensland, Australia

In Queensland, Australia, there is presently a high level of interest in long-rotation hardwood plantation investments for sawlog production, despite the consensus in Australian literature that such investments are not financially viable. Continuing genetics, silviculture and processing research, and increasing awareness about the ecosystem services generated by plantations, are anticipated to make future plantings profitable and socio-economically desirable in many parts of Queensland. Financial and economic models of hardwood plantations in Queensland are developed to test this hypothesis. The economic model accounts for carbon sequestration, salinity amelioration and other ecosystem service values of hardwood plantations. A carbon model estimates the value of carbon sequestered, while salinity and other ecosystem service values are estimated by the benefit transfer method. Where high growth rates (20-25 m(3) ha(-1) year(-1)) are achievable, long-rotation hardwood plantations are profitable in Queensland Hardwood Regions 1, 3 and 7 when rural land values are less than $2300/ha. Under optimistic assumptions, hardwood plantations growing at a rate of 15 in 3 ha-1 year 1 are financially viable in Hardwood Regions 2, 4 and 8, provided land values are less than $1600/ha. The major implication of the economic analysis is that long-rotation hardwood plantation forestry is socio-economically justified in most Hardwood Regions, even though financial returns from timber production may be negative. (c) 2003 Elsevier B.V. All rights reserved.

Analysis of rubber vulcanisates

A study has been made, using High Pressure Liquid Chromatography, of the migration of TMQ (a quinoline type) and 6PPD (a paraphenylenediamine type) antidegradants from a tyre sidewall compound into adjacent casing and liner compounds containing no antidegradant. Migration takes place at a rapid rate, even during the vulcanisation of the composite. After 4000 hours ageing in nitrogen at 100oC, there is a higher level of antidegradants in the casing than in the sidewall. An equilibrium distribution is not obtained. After 114 days at 50oC in 95% relative humidity, the level of solvent extractable 6PPD fell to zero, but subsequent ageing for 2 years in 50 pphm ozone showed no evidence of sidewall cracking. It is suggested that the antidegradant is still active but linked to the polymer chain. An analytical method, for the type and amount of sulphenamide accelerators in vulcanised rubber compounds, has been developed. During the vulcanisation process, the accelerators decay, liberating specific amines which have been solvent extracted, derivatised with 1-chloro-2,4-dinitrobenzene and the yellow coloured zwitter ion analysed using High Pressure Liquid Chromatography. The decay of the accelerator and sulphur during the vulcanisation process, has been studied. It has been demonstrated that the sulphur crosslinking with a styrenebutadiene polymer is a first order reaction, after an initial period during which the accelerator content falls to zero. Variations in sulphur to accelerator ratios gave consistent rate constants for the crosslinking, except for a sulphur level of less than 1% by weight and a ratiio of accelerator to sulphur of 1:1.3. The retention time of the reaction product between sulphur and accelerator from an HPLC column changes with cure time, showing that the precurser to crosslinking is an ever changing material. One of these reaction products has been analysed.

Mechanisms of antifatigue agents used in natural rubber

A large number of compounds containing quinonoid or hindered phenol functions were examined for their roles as antifatigue agents. Among the evaluated quinones and phenols expected to have macroalkyl radical scavenging ability, BQ, αTOC, γTOC and GM showed relatively good performance for fatigue resistance (although their performance was slightly less effective than the commercial aromatic amine antioxidants, IPPD and 6PPD). The compounds which were shown to have higher reactivity with alkyl radicals (via calculated reactivity indices) showed better fatigue resistance. This fact supports the suggestion that strong alkyl radical scavengers should be also effective antifatigue agents. Evidence produced based on calculation of reactivity indices suggests that the quinones examined react with alkyl radicals on the meta position of the quinone rings producing phenoxyl radicals. The phenoxyl radicals are expected either to disproportionate, to recombine with a further alkyl radical, or to abstract a hydrogen from another alkyl radical producing an olefine. The regeneration of quinones and formation of the corresponding phenols is expected to occur during the antifatigue activity. The phenol antioxidant, HBA is expected to produce a quinonoid compound and this is also expected to function in a similar way to other quinones. Another phenol, GM, which is also known to scavenge alkyl radicals showed good antifatigue performance. Tocopherols had effective antifatigue activity and are expected to have different antifatigue mechanisms from that of other quinones, hence αTOC was examined for its mechanisms during rubber fatiguing using HPLC analysis. Trimers of αTOC which were produced during vulcanisation are suggested to contribute to the fatigue activity observed. The evidence suggests that the trimers reproduce αTOC and a mechanism was proposed. Although antifatigue agents evaluated showed antifatigue activity, most of them had poor thermoxidative resistance, hence it was necessary to compensate for this by using a combination of antioxidants with the antifatigue agents. Reactive antioxidants which have the potential to graft on the polymer chains during reactive processing were used for this purpose. APMA was the most effective antioxidant among other evaluated reactive antioxidants. Although high ratio of grafting was achieved after optimisation of grafting conditions, it is suggested that this was achieved by long branches of APMA due to large extent of polymerisation. This is expected to cause maldistribution of APMA leading to reducing the effect of CB-D activity (while CB-A activity showed clear advantages for grafting). Further optimisation of grafting conditions is required in order to use APMA more effectively. Moreover, although synergistic effects between APMA and antifatigue agents were expected, none of the evaluated antifatigue agents, BQ, αTOC, γTOC and TMQ, showed significant synergism both in fatigue and thermoxidative resistance. They performed just as additives.

Individual differences in work behaviour of blue-collar workers : a study of rubber tappers in Malaysia

This thesis examines individual differences in work behaviour of rubber tappers. The study examined sex, age, experience and race differences and their interactions with terrain on job performance, absenteeism, and job satisfaction of 1053 rubber tappers. Rubber tappers are unskilled blue-collar workers who essentially do the same type of work and are paid the same rates of pay. There are very few studies that have compared male and female blue-collar workers doing similar jobs in organisational settings. This study is one of the few investigations that examine sex differences in job performance of blue-collar workers doing same job using production data. Studies on age differences in work behaviour encounter numerous methodological difficulties such as high turnover, internal transfers and problems associated with age differences in educational levels. The participation of rubber tappers in this study is envisaged to overcome these difficulties because attrition rates of rubber tappers are low, and internal transfers are non existent. Further, the educational levels of rubber tappers are relatively similar across different age cohorts, as most rubber tappers have little or no education. Two measures of both job performance and absenteeism were derived from payroll records. The two job performance measures were total crop production and attendance. The two absenteeism measures were avoidable and unavoidable absence rates. Overall job satisfaction was determined using a 4-item scale. Significant sex, age, experience and race differences were obtained for job performance, absenteeism and job satisfaction. Significant interactive effects were also obtained for sex, age , experience, race and terrain for job performance and absenteeism. The results are discussed in relation to the abilities and motivation of rubber tappers. The implication of these findings for employee selection and human resource management in rubber estates is discussed.