Academic literature on the topic 'Eucalyptus delegatensis'

In the dry uneven-aged eucalypt forests of central Tasmania the establishment of seedlings of Eucalyptus delegatensis requires a mitigation of the competition provided by the understorey, regeneration being observed to follow both fire and cultivation. Most of the adult trees of E. delegatensis survive even severe fires, although there can be considerable later mortality associated with mechanical failure of the base of the trunk. E. delegatensis dry forest usually has a distinctive sapling layer. Fire kills most of these saplings, the mortality rate being inversely related to their height and bark thickness.

Six Eucalyptus species, E. regnans F. Muell., E. delegatensis R.T. Bak., E. globulus Labill., E. nitens (Deane & Maid.) Maid., E. pauciflora Sieb. ex Spreng, and E. grandis Hill ex Maid., were sampled for determination of frost hardiness in March (late summer) and August (late winter) 1985 from trial plantings at four elevations in southern Tasmania. In March, there was a statistically significant difference between sites, but not between species or provenances. In August, significant differences between species, and for E. delegatensis between provenances, had developed. The species ranked in order of increasing frost hardiness as follows: E. regnans < E. grandis < E. globules = E. delegatensis (Maydena provenance) < E. pauciflora < E. nitens < E. delegatensis (Guildford provenance). Greatest frost hardiness was developed at the 60-m site (elevation), followed by (in decreasing order) the 650-m site, the 440-m site, and the 240- m site. This order corresponded to the minimum temperatures experienced at the sites. Conversely, greatest growth occurred at the 60-and 240-m sites followed by the 440-m site and then the 650-m site, corresponding to decreasing maximum temperatures. It is argued that good growth and productivity are possible on quite frost prone sites, provided suitable provenances are selected for planting.

Eucalyptus delegatensis R.T. Baker subsp. delegatensis is an interval-sensitive, fire-killed eucalypt that dominates large tracts of montane forest in the Australian Alps. Although it has been widely accepted in forest management that E. delegatensis takes 20 years to flower and fruit after stand-replacing fire events, recent observations after high intensity fires in the Australian Alps have shown that early flowering and fruiting is occurring from what can be termed ‘precocious’ individuals in some areas. In some instances, early flowering and fruit set is occurring within 6 years after stand-replacing fire. One historical study in the Australian Capital Territory had noted that such seed was viable, but we found no reported experiments documenting this or detailing the degree of viability. Here we discuss the results of a germination experiment undertaken on seed collected from Namadgi National Park from early-maturing alpine ash trees. Although at the low end of known viability estimates for E. delegatensis, seed from these individuals was nonetheless found to be viable, with a mean of 455 (s.d. = 139) germinants per 10 g of chaff and seed mix. We discuss this result in relation to fire management in the Australian Alps and suggest further research that needs to be undertaken to better document and understand the phenomenon.

Se analiza la capacidad de retoñación de 5 especies del género Eucalyptus, E. delegatensis, E. globulus ssp. globulus, E. nitens, E. regnans y E. viminalis. Un año después de la corta sólo E. regnans no presentaba una retoñación suficiente como para asegurar la siguiente rotación de monte bajo. Las otras especies retoñaron bien, incluso E. nitens y E. delegatensis, especies que tradicionalmente se han considerado con ciertas limitaciones para rebrotar después de la corta.

Seedlings, saplings and mature eucalypts were susceptible to infection by Endothia gyrosa and Botryosphaeria ribis. Eucalyptus regnans and E. delegatensis were more susceptible than E. grandis and E. saligna. In trees not subjected to stress, cankers were limited in extent and often healed. When trees were defoliated, either manually or by severe insect attack, stem concentrations of both starch and soluble carbohydrates were reduced and canker development in some pathogen/host combinations was increased. Seedlings subjected to water stress were not predisposed to canker formation. The association of E. gyrosa with branch dieback of rural eucalypts suffering from chronic defoliation suggests that canker fungi contribute to the crown dieback syndrome in south-eastern Australia.

In Australia the ash group of eucalypts comprises approximately 35 species of Eucalyptus from the botanical series Obliquae. They are abundant in south-eastern Australia, but timber of commerce comes mainly from Victoria and Tasmania and includes E. regnans F. Muell., E. delegatensis R.T. Baker and E. obliqua L'Hérit. This group produces some of the fastest growing and the highest yielding hardwood species in Australia. The timbers are similar in appearance and can be interchanged for many uses, but there are some important differences. This study found differences between the species in basic density, distinctness of growth rings and pore grouping, ray width, proportion of multiseriate rays, and the height of the multi seriate proportion of the rays. Differences between mainland and Tasmanian provenances were also observed. Growth rings are prominent in E. delegatensis from the mainland, but less so from Tasmania, and least distinct in E. obliqua. Basic density can be used to distinguish E. obliqua when samples are heavier than 605 kg/ m3, and E. regnans for samples less than 390 kg/m3. Height of the multiseriate portion of the rays is 1-9, mostly 5 cells in E. obliqua, whereas it is 1-5, mostly 1-2(-4) cells high in the other two species; maximum height of the multi seriate portion of the rays is 3-12, mostly 4-8 cells in E. obliqua, 1-6, mostly 1-2 cells in E. delegatensis, and 1-8, mostly 1-3 cells in E. regnans; width of individual ray cells 10-30 µm, mostly 15-20 µm in E obliqua, and 5-16 µm, mostly 8-12 µm in the other two species. A key for separation between the species is given and the similarities to other species are discussed. Other commercially important species will be dealt with subsequently.

The use of calibrated near infrared (NIR) spectroscopy for the prediction of a range solid wood properties is described. The methods developed are applicable to large-scale nondestructive forest resource assessment and to tree breeding and silvicultural programs. A series of Eucalyptus delegatensis R.T. Baker (alpine ash) samples were characterized in terms of density, longitudinal modulus of elasticity (EL), microfibril angle (MFA), and modulus of rupture (MOR). NIR spectra were obtained from the radial–longitudinal face of each sample and used to generate calibrations for the measured physical properties. The relationships were good in all cases, with coefficients of determination ranging from 0.77 for MOR through 0.90 for EL to 0.93 for stick density. In view of the rapidly expanding range of applications for this technique, it is concluded that appropriately calibrated NIR spectroscopy could form the basis of a "universal" testing instrument capable of predicting a wide range of product properties from a single type of spectrum obtained from the product or from the raw material.

We report spotlight and camera-trap observations of Leadbeater’s possum (Gymnobelideus leadbeateri) at six locations up to 15km east of its described range. Half of our records occurred in fire-affected, mixed-species forest, with a tree species and seral stage composition that differs markedly from its predominant habitat: late-mature forests dominated by Eucalyptus regnans, E. delegatensis and E. nitens.

Despite the recognised significance of hyphomycetes in the degradation of leaf litter in streams, few studies have been carried out in alpine environments and none in Australian alpine streams. We hypothesised that the fungal communities responsible for leaf decomposition would change over immersion time, and would respond differently at different sites and on different types of vegetation. Leaf bags containing Epacris glacialis (F. Muell.), Eucalyptus pauciflora (Sieber ex. Spreng) and Eucalyptus delegatensis (R.T. Baker) were deployed at different sites in a stream in the Victorian Alpine National Park, south-eastern Australia. Leaf colonisation was delayed for 2 weeks and decay constants for E. pauciflora and E. delegatensis were 0.004–0.005 and 0.006 respectively. Maximum fungal biomass on leaves was similar to that in previous published studies, whereas sporulation rates were two or three orders of magnitude lower, indicating a reduced reproductive effort. Sporulation and DNA-based studies combined showed that fungal communities on the decomposing leaf material changed over time and exhibited significant preferences for leaf type and study site. We have shown that aquatic hyphomycetes can degrade physically tough leaves of Australian alpine plant species, potentially contributing to pathways for particulate carbon to enter alpine-stream food webs.

The frost resistance of Eucalyptus delegatensis is shown to vary with seedling age over the first 6 months of development. Much of this variation is a result of the differing sensitivity of leaves originating from different leaf nodes, although older leaves from the same node may be more frost resistant than recently expanded leaves. Newly emergent seedlings appear to be the most susceptible stage of the tree's lifecycle to death by frost.

Steam reconditioning to recover collapse, in mid to low density eucalypt species, has been known for over ninety years. The current industrial practices for steam reconditioning have largely been based on a few older studies, which were often poorly documented and based on very small sample sizes. On top of this, many local practices and ‘rules of thumb’ have developed over time, many of which have a questionable scientific basis. This thesis was undertaken to more rigorously investigate and fundamentally understand collapse recovery, and try to optimise its application. The most obvious variable that kiln operators have control over is the moisture content of the timber prior to steam reconditioning. Experiments were undertaken to generate a range of moisture gradients (ranging from minimal to more industrially realistic) to evaluate the effect of moisture content on collapse recovery. An optimal moisture content for the core of the boards was found to be between about 18–20%, although there was no statistical difference in recoveries between about 17–25% moisture content. Below 15% moisture content recovery dropped off severely and intra-ring internal checking closure was incomplete, while at 25% moisture content an increased level of normal shrinkage, due to the early removal of drying stresses, was the main drawback. Above a core moisture content of about 35% incomplete closure of intra-ring internal checks was again observed. There was little evidence of re-collapse occurring in these high moisture content samples. Previously established relationships between density and collapse and drying rate were again generally observed in these experiments. However, for the first time an effect of collapse in reducing the fitted drying diffusion coefficients was also observed. It was also observed that, provided the moisture content of the board was in the critical range, most of the collapse recovery was achieved in the time it took to get the core of the board up to the steaming temperature of close to 100°C. This suggests that for most thicknesses a conservative reconditioning period of two hours at temperature is all that is required. This recommended shortening of the reconditioning cycle could dramatically increase the throughput of timber through the steam reconditioning chambers. Alternatively, it could mean that where modern final drying kilns are being used, the reconditioning treatment could be carried out within the final drying kiln. A finite element model was developed to demonstrate the mechanism by which collapse recovery occurs. The theory tested was that the elastic component that stores the energy to restore the shape of the deformed cell is primarily found in the S1 and S3 layers. In contrast, the inelastic component is primarily found in the S2 layer. The model generated here provided limited support for this theory.

Doctor of Philosophy
Steam reconditioning to recover collapse, in mid to low density eucalypt species, has been known for over ninety years. The current industrial practices for steam reconditioning have largely been based on a few older studies, which were often poorly documented and based on very small sample sizes. On top of this, many local practices and ‘rules of thumb’ have developed over time, many of which have a questionable scientific basis. This thesis was undertaken to more rigorously investigate and fundamentally understand collapse recovery, and try to optimise its application. The most obvious variable that kiln operators have control over is the moisture content of the timber prior to steam reconditioning. Experiments were undertaken to generate a range of moisture gradients (ranging from minimal to more industrially realistic) to evaluate the effect of moisture content on collapse recovery. An optimal moisture content for the core of the boards was found to be between about 18–20%, although there was no statistical difference in recoveries between about 17–25% moisture content. Below 15% moisture content recovery dropped off severely and intra-ring internal checking closure was incomplete, while at 25% moisture content an increased level of normal shrinkage, due to the early removal of drying stresses, was the main drawback. Above a core moisture content of about 35% incomplete closure of intra-ring internal checks was again observed. There was little evidence of re-collapse occurring in these high moisture content samples. Previously established relationships between density and collapse and drying rate were again generally observed in these experiments. However, for the first time an effect of collapse in reducing the fitted drying diffusion coefficients was also observed. It was also observed that, provided the moisture content of the board was in the critical range, most of the collapse recovery was achieved in the time it took to get the core of the board up to the steaming temperature of close to 100°C. This suggests that for most thicknesses a conservative reconditioning period of two hours at temperature is all that is required. This recommended shortening of the reconditioning cycle could dramatically increase the throughput of timber through the steam reconditioning chambers. Alternatively, it could mean that where modern final drying kilns are being used, the reconditioning treatment could be carried out within the final drying kiln. A finite element model was developed to demonstrate the mechanism by which collapse recovery occurs. The theory tested was that the elastic component that stores the energy to restore the shape of the deformed cell is primarily found in the S1 and S3 layers. In contrast, the inelastic component is primarily found in the S2 layer. The model generated here provided limited support for this theory.

The forests of south-eastern Australia, having evolved in one of the most fire-prone environments in the world, are characterized by many adaptations to recovery following burning. Thus forest ecosystems are characterized by rapid regenerative capacity, from either seed or re-sprouting, and mechanisms to recover nutrients volatilized, including an abundance of N2 fixing plants in natural assemblages. Soil physical, chemical and biological properties are directly altered during fire due to heating and oxidation of soil organic matter, and after fire due to changes in heat, light and moisture inputs. In natural ecosystems, carbon (C) and nitrogen (N) lost from soil due to fires are recovered through photosynthesis and biological N2 fixation (BNF) by regenerating vegetation and soil microbes.
This study investigated post-fire recovery of soil C and N in four structurally different sub-alpine plant communities (grassland, heathland, Snowgum and Alpine ash) of south-eastern Australia which were extensively burnt by landscape-scale fires in 2003. The amount and isotopic concentration of C and N in soils to a depth of 20 cm from Alpine ash forest were assessed five years after fire in 2008 and results were integrated with measurements taken immediately prior to burning (2002) and annually afterwards.
Because the historical data set, comprised of three soil samplings over the years 2002 to 2005, consisted of soil total C and N values which were determined as an adjunct to 13C and 15N isotopic studies, it was necessary to establish the accuracy of these IRMS-derived measurements prior to further analysis of the dataset. Two well-established and robust methods for determining soil C (total C by LECO and oxidizable C by the Walkley-Black method) were compared with the IRMS total C measurement in a one-off sampling to establish equivalence prior to assembling a time-course change in soil C from immediately pre-fire to five years post-fire. The LECO and IRMS dry combustion measurements were essentially the same (r2 >0.99), while soil oxidizable C recovery by the Walkley-Black method (wet digestion) was 68% compared to the LECO/IRMS measurements of total C. Thus the total C measurement derived from the much smaller sample size (approximately 15 mg) combusted during IRMS are equivalent to LECO measurement which require about 150 mg of sample.
Both total C and N in the soil of Alpine ash forests were significantly higher than soils from Snowgum, heathland and grassland communities. The ratio of soil NH4+ to NO3- concentration was greater for Alpine ash forest and Snow gum woodland but both N-fractions were similar for heathland and grassland soils. The abundance of soil 15N and 13C was significantly depleted in Alpine ash but both isotopes were enriched in the heathland compared to the other ecosystems. Abundance of both 15N and 13C increased with soil depth.
The natural abundance of 15N and 13C in the foliage of a subset of non-N2 fixing and N2 fixing plants was measured as a guide to estimate BNF inputs. Foliage N concentration was significantly greater in N2 fixers than non-N2 fixers while C content and 13C abundance were similar in both functional groups. Abundance of 15N was depleted in the N2 fixing species but was not significantly different from the non-N2 fixers to confidently calculate BNF inputs based on the 15N abundance in the leaves.
The total C pool in soil (to 20 cm depth) had not yet returned to the pre-fire levels in 2008 and it was estimated that such levels of C would be reached in another 6-7 years (about 12 years after the fire). The C and N of soil organic matter were significantly enriched in 15N and 13C isotopes after fire and had not returned to the pre-fire levels five years after the fire. It is concluded that the soil organic N pool can recover faster than the total C pool after the fire in the Alpine ash forests.

A major factor limiting the growth of E. delegatensis is low temperature. This is important both in the natural distribution of the species and as a plantation species both within Australia and elsewhere. This project deals with aspects of the frost hardiness of E. delegatensis including the seasonal variation, genetic variation and comparison with other species of eucalypts. The diffusate electrical conductivity method for measuring frost hardiness of plant tissue was adapted and developed for use with an air-filled frost chamber. The major adaptation was the addition of an ice nucleation agent, silver iodide, to tissue samples during test freezing to prevent supercooling. A thorough evaluation showed that this method is sensitive enough to detect differences of 0.3°C and would be useful for screening large numbers of plants for breeding. Seven provenances of E. delegatensis planted in two provenance trials (planted in 1979) at Tarraleah and Myrtle Bank, Tasmania, were tested for frost hardiness. Plants at Tarraleah were tested at approximately six week intervals throughout 1984, while at Myrtle Bank they were tested three times during the hardening phase. Seasonal differencesin frost hardiness ranged from 2.4°C for the Bicheno provenance (the least hardy) to 4.6°C for the Ben Lomond provenance (the most hardy) at Tarraleah. The maximum hardiness reached ranged from -6.0°C for the Bicheno provenance to -8.6°C for the Ben Lomond provenance at Tarraleah while at Myrtle Bank the range was from -4.7°C for the Bicheno provenance to -7.7°C for the Ben Lomond provenance. The same ranking of provenances at maximum frost hardiness was obtained at both trials. Laboratory simulation of hardening conditions with night temperatures of 12, 4 and 0°C showed that colder night temperatures resulted in greater development of frost hardiness for all provenances tested. The ranking of provenances for frost hardiness corresponded to the field trial. A field trial in the Esperance Valley, Tasmania, (planted in 1983) had two provenances each of E. delegatensis, E. nitens, E. regnans and E. globulus planted at altitudes of 60, 240, 440 and 650 m. One provenance of E. grandis was planted at the 60 and 240 m sites and one provenance of E. pauciflora at the 440 and 650 m sites. All species were tested forfrost hardiness in March and August of 1985. There was no significant difference between species or provenances in March. In August the only species with a significant difference between provenances was E. delegatensis, Significant differences between species were measured in August, when the species ranked in decreasing order of frost hardiness as follows: E. deIegatensis = E. nitens > E. pauciflora > E. globulus > E. grandis > E. regnans. It was found that the lowest minimum temperatures occurred at the 60 m site followed by the 650 m site then the 440 m site with the 240 m site having the highest minimum temperatures. The frost hardiness of the plants tested also followed this pattern with the greatest development of frost hardiness at the 60 m site. Growth of the plants corresponded to the altitudinal sequence with most height and diameter growth at the 60 and 240 m sites which experienced the warmest maximum temperatures. The development of a reliable method of testing plant tissue for frost hardiness is important for plant breeding, since both seedlings and established plants can be tested. Testing of established E. delegatensis showed that there is significant variation in frost hardiness within the species and that there is no significant interaction between frost hardiness and site within Tasmania. Frost hardiness development in E. delegatensis is a response to low night temperatures and is independent of day temperature and growth rate. E. delegatensis compared favourably with other commercially planted species of eucalypts in terms of frost hardiness. It was shown that it is possible to achieve good growth of eucalypts on a frost-prone site provided suitable provenances are planted.

Ectomycorrhizal fungi underpin critical ecosystem processes which affect tree health. Eucalypt decline is widespread throughout Australia, and its cause has been attributed to a variety of factors, including forest management. In Tasmania, dieback in Eucalyptus delegatensis R.T. Baker has been linked to altered fire regimes and associated changes in mycorrhizal communities. This thesis presents a study that explores ectomycorrhizal species richness and community composition in relation to eucalypt health, understorey vegetation and soil chemistry in the context of fire history. The results further our understanding of ectomycorrhizal ecology and elucidate factors important to the maintenance of a healthy forest ecosystem. Study sites were established in E. delegatensis forest with either sclerophyll understorey (six plots) or rainforest understorey (six plots). Eight of the plots, located in north-east Tasmania, had been established for a study of fire ecology and had known fire histories ranging from 42 years since the last fire to long unburnt (>120 years). Four plots located in north-western Tasmania were long unburnt but had been disturbed by logging 22-25 years previously. Ectomycorrhizal fungal sporocarps, root tips and soil samples were collected during a three-year period from all 12 plots. Samples from soil, root tips and sporocarps gave rise to different but complementary information about ectomycorrhizal communities. Fungal operational taxonomic units were identified through DNA sequencing and phylogenetic analysis. At each site, understorey vegetation was characterised, soil and eucalypt foliage chemistry was analysed, and eucalypt crown condition was assessed. Primary crown dieback was identified as the most effective method for the measurement of eucalypt health. Multivariate statistical analyses were used to explore the relationships among ectomycorrhizal communities, eucalypt health, vegetation and abiotic variables. E. delegatensis forest with rainforest understorey was more than likely to be affected by severe eucalypt decline, had higher concentrations of soil inorganic nitrogen (nitrate and ammonium) and eucalypt foliar nitrogen, and had lower concentrations of soil and eucalypt foliar phosphorus, than forest with sclerophyll understorey. As forest declined in health the ecosystem moved from being nitrogen limiting to phosphorus limiting due to reduced phosphorus availability and plant uptake, potentially due to altered mycorrhizal activity. Ectomycorrhizal communities differed between moderately and severely declining forest and were correlated to crown health and altered soil chemistry associated with the two levels of decline. The Cortinariaceae had high species richness in healthiest sites while the Russulaceae and Thelephoraceae were rich in forest affected by severe decline. In northwestern and north-eastern Tasmania unique and distinctly different ectomycorrhizal fungal communities were found to occur in E. delegatensis forest with rainforest understorey versus those with sclerophyll understorey. Irrespective of understorey type and health status, the Cortinariaceae were highly diverse, and were the most species-rich family within the ectomycorrhizal community of E. delegatensis forest. The Cortinariaceae also was the most abundant family in the root tip community. The Helotiales, Russulaceae and Thelephoraceae also were important components. The importance of the Cortinariaceae in E. delegatensis forest is similar to other Australian eucalypt forests but distinctly different from northern hemisphere forests, which tend to be dominated by the Russulaceae, Thelephoraceae and Corticeaceae. Distance-based multiple linear regression models using only significant predictor variables based on soil and foliage nutrient concentrations and crown health were able to explain 52% of the variation in fungal community composition, and 44% of the variation in ectomycorrhizal community proportional composition at the family level. Soil pH, total soil nitrate, soil organic carbon and soil phosphorus were significant in predicting ectomycorrhizal species composition and proportional composition in the final models. A multiple linear regression model showed that available soil nitrate and phosphorus were significant in predicting ectomycorrhizal community richness. High richness was associated with low available soil nitrate or phosphorus. Northern hemisphere studies which show that changes in soil chemistry, especially mineral nitrogen, can strongly influence mycorrhizal species richness, species composition and community structure corroborate the likely influence of soil nitrogen on the ectomycorrhizal communities of E. delegatensis forest. This is the first study to find a strong correlation between ectomycorrhizal fungal communities and the status of eucalypt forest health. The results support the currently proposed model that, in the absence of fire, premature decline of temperate Australian eucalypt forests is closely linked to changes in soil chemistry, understorey vegetation and mycorrhizal communities.

Eucalyptus delegatensis is a widespread dominant of montane forests in southeastern Australia, where is occupies sites of widely varying moisture status and understorey type. The age and size class distributions of E. delegatensis on 23 sites of varying precipitation over its range on dolerite in Tasmania are strongly related to the floristic composition of the understorey vegetation and to moisture availability. No stands are even-aged, but all stands exhibit evidence of periodic rather than continuous recruitment; the periodicity of past recruitment events increasing with more mesic conditions. There is evidence for a change towards less frequent recruitment events in the higher rainfall stands since white settlement. An explanation for the variations in regeneration patterns is sought in the complex interactions between climate, fire frequency, fire intensity and understorey vegetation type. The trees in multi-aged forests at the dry end of the environmental range of E, delegatensis are extremely fire resistant while the survival of the even-aged saplings is dependent upon their height and bark thickness. Regeneration typically follows forest fire but experimental studies showed that germinates readily establish on cultivated seedbeds. Marked intraspecific competition occurs between the regeneration and the overwood trees. Experiments with germinates, seedlings, and advance growth indicate that soil drought prohibits rapid growth of regeneration beneath overwood while the higher levels of moisture available in forest gaps supports a dense stocking of vigorously growing saplings, Total removal of canopy cover results in a microclimate with greater maximum and lower minimum ground surface temperatures than in an environmentally similar unlogged stand. The poor health of regeneration on some high-altitude clear-felled forest sites is explained by the interactions of canopy cover, frost damage and topography. The various types of eucalypt silvicultural practices are subjectively classified as intensive, partial and selective systems. It is suggested that dry E. delegatensis forests are well suited to selective logging.

Land managers increasingly are being involved in making quantitative evaluation of management options. Forests, however, are complex biological systems and predictions require the synthesis of many processes. Traditional approaches to evaluating options have been to replicate experiments in time and space. Not all questions are amenable to such approaches, and even where they are, inferences may be of only limited application. In an increasingly complex decision making context, land managers will require access to more sophisticated techniques. This thesis illustrates the collection of basic data, its synthesis into a physiological model, and its use as a tool to address a typically complex management question - the time at which Eucalyptus delegatensis R.T.Baker seed should be sown in forest regeneration operations. The species is widely exploited for commercial forestry in South-Eastern Australia and its germination physiology is moderately complex, providing an appropriate test for the usefulness of the modelling approach. The germination response of seedlots from five provenances to temperature, stratification, soil matric potential and interrupted imbibition was examined. The species was found to have a distinct temperature optimum between 15 and 20°C, and a minimum temperature for germination of approximately 2°C. Short periods of exposure to high temperatures did not substantially affect germination performance. Stratification greatly increased the range of temperatures over which a high proportion of the seed germinated. Increases in the rate of germination with stratification are related to accrued thermal time during stratification. Pre-imbibing seeds at water potentials down to -2 MPa increased the rate of germination. However, no advantage was found after pre-imibibing at lesser soil water matric potentials. This increased germination rate was associated with a shortening of the time to commencement of germination and more synchronous germination. Germination rate and germination capacity were impeded by soil matric potentials below -0.01 .MPa, and germination was totally inhibited by soil matric potentials below -0.5 MPa. Soil matric potential and temperature interacted in their effects on germination capacity, and seeds germinating at near optimum temperatures were less sensitive to soil moisture stress. Seeds survived dehydration within sixty hours of the commencement of imbibition, but were increasingly affected by dehydration thereafter. The rate of imbibition was influenced by the ambient temperature and solution water potential. At modest levels of water stress imbibition was not impeded and the observed reduction in gennination capacity was probably due to the inhibition of ii growth related processes. Differences in germination response were detected between the seedlots and these could be related to their geographic brigin. The proportion of variability in seed and germination traits attributable to interand intra-site components varied between traits examined. The germination rate of seed was not significantly different between trees within a site, or between trees from different sites. Variation in seed size and the proportion of dormant seed in seed samples was mainly affected by site effects. The sensitivity of seed samples to the water stress levels applied also varied substantially between sites but additionally the seed from the drier site exhibited a highly significant between-tree variability. It was concluded that the proportion of variation in seed and germination characteristics attributable to between-, and to within-site effects, could be partly related to the scale at which selective forces were presumed to operate. Nevertheless, a substantial amount of variation in response existed within the seed collected from the one tree. The role of age and microtopographical variation in enabling seedlings to withstand frost and drought was explored in glasshouse studies. The frost resistance of E. delegatensis was found to vary with seedling age over the first six months of development. Much of this variation was found to be a result of the differing sensitivity of leaves originating from different leaf nodes, although older leaves from the same node may have been more frost resistant than recently expanded leaves. Newly emergent seedlings appeared to be the most susceptible stage of the tree's lifecycle to death by frost. Small scale variation in soil conditions, at the scale of tens of centimetres, markedly affected the germination and establishment of seeds and seedlings under moisture limiting conditions. Microsites that afforded protection, and probably resulted in increased humidity, caused a marked increase in germination number and rate. The mean survival time was significantly higher on these protected microsites than on less protected microsites, or on microsites that restricted root penetration. The importance of this variability in microtopography was strongly influenced by season and the level of environmental stress, and was diminished as seedlings aged. Due to the different requirements for seed germination and seedling growth, a favourable microsite for germination was not necessarily a favourable site for seedling survival. A comparison of seed and seedling responses to water stress indicated that for E. delegatensis, at least, selection due to microsite differences at the time of germination may not affect the developmental characteristics of the seedlings. iii At two geographically close sites that differed significantly in climatic profile, seed of E. delegatensis and Eucalyptus amygdalina Labill., a species that frequently replaces E. delegatensis on drier sites, was sown at twelve times of the year. Regular censuses of seedlings were conducted. The pattern of survival of over twenty thousand seedlings, comprising one thousand two hundred identified cohorts was followed. The influences of weather, seed harvesting, site preparation, time of emergence and time of sowing on emergence, growth and survival were examined. By modelling temperature and soil moisture it was found that germination in the field was influenced strongly by ambient temperature and soil moisture and that the commencement of germination flushes in spring and autumn were well correlated to threshold values of soil moisture and air temperature predicted from laboratory studies. A model of seasonal patterns of seedling mortality was developed and concluded to be highly age dependant. Although age dependant mortality rate was relatively constant at a given site between seasons and years, with each season containing its own compliment of hazards, it was necessary to make allowance for stochastic events, such as severe frosts and drought, to satisfactorily model survivorship. A mathematical model of germination was developed for E. delegatensis based on the physiology of underlying processes. The accuracy of this model in predicting the time course of germination under conditions of fluctuating temperature and moisture was examined. This model was used to examine the results from the field trial. In combination with a mortality function derived from field observation, this gennination model was used to make recommendations on the optimum times of sowing for the east coast of Tasmania, to explore the importance of 'safe sites' for germination, and to investigate the implications of different seedlot dormancy responses on reproductive success.

Partial logging in high-altitude E. delegatensis forests involves the retention of approximately 50 % of original forest basal area, and was implemented to overcome the problem of "growth check" in regenerating eucalypts following clearfelling. It is increasingly being carried out in these forests in an effort to provide income to landowners while still allowing regeneration of the overstorey eucalypts. This thesis looks at the effects of partial logging on understorey floristics and structure in both, the short (-2 years), and the long (15-20 years) term. Analysis of a floristic, structural and environmental dataset using multivariate and ANOVA techniques found that two understorey types, grassy and shrubby, were present, and that short term trends included reduced cover of all lifeform groups, reduced understorey height, species richness and structural complexity, and increased bare ground cover and soil disturbance. Four of these trends, increased grass and forb cover, decreased shrub cover and structural complexity, were still apparent 5-8 years after logging, and two, reduced shrub cover and habitat complexity, 16-21 years after logging, particularly in shrubby forest. These changes were attributed to the reduced cover of the overstorey and subsequent changes in the light/temperature/moisture regimes of the forest floor microclimate. Effects of plantation establishment in wetter areas of this forest type were similar to those of partial logging, but of a greater magnitude and duration. Ecological processes structuring the understorey were examined by, first, looking at changes in species cover/abundance under individual overstorey eucalypts and in forest gaps in unlogged forest, and, second, with a laboratory shading/disturbance experiment. It was found that canopies of overstorey eucalypts were causing distinct patterns in understorey distribution. Species richness and cover increased moving from trunk to canopy edge to forest gap and from unshaded to shaded sector of forest gaps primarily due to the inhibitory effects of high litter and shade under trees, and cold induced photoinhibition in high light areas of gaps. Chlorophyll fluorescence measurements confirmed the requirement of shade for, the shrub Lomatia tinctoria, and the sedge Lomandra longifolia, and the ability of grasses to out compete these species in full sun, mimicking the patterns observed logged forest. Results are discussed in relation to the theory of ecological resilience and it is suggested that increasing divergence of understorey will occur with each logging and/or plantation rotation and may lead to shifts in forest/grassland boundaries.

Understanding the way plants respond to their environment is a central aim in plant ecology, as these responses are what fundamentally influence ecosystem function. Plant functional traits describe morphological, physiological, and phenological characteristics that affect overall plant fitness through their influence on survival, growth, and reproduction. Functional traits are heralded as a dynamic, representative, and simple way to capture plant response and predict ecosystem processes. In recent years, there has been a focus on understanding trait patterns that emerge along abiotic environmental gradients, however there is little research on the role of the biotic environment, a key aspect underpinning plant co-existence. This study aimed to address whether there is, in fact, a functional trait response to biotic influences, in an experimental forest, or if responses are due to microclimate alone. This research took place at the Australian Forest Evenness Experiment (AFEX), Using this experimental forest provides a unique opportunity to investigate neighbourhood interactions, where the density and spatial patterning of individuals is the result of experimental manipulation, rather than a consequence of variation in abiotic conditions. Four species, Eucalyptus regnans, Eucalyptus delegatensis, Pomaderris apetala and Acacia dealbata, were measured for six plant functional traits: specific leaf area (SLA), leaf dry matter content (LDMC), predawn water potential (Ψleaf), bark thickness, foliar nitrogen content (Nleaf), and the leaf area to sapwood area ratio (LA:SA). I found that neighbourhood interactions influence plant functional traits in ways that are highly dependent on the species involved. The effect of traits was often not mediated by microclimate although competition for light was common. I demonstrated that the functional traits of E. delegatensis, particularly those related to water relations, were significantly altered in the presence of P. apetala neighbours, indicating a strong competitive interaction between the two species for water. E. regnans, on the other hand, did not adjust its traits in response to P. apetala. In contrast, E. delegatensis and E. regnans did not display strong trait responses to the neighbourhood effect of the other, and therefore may not be directly competing. In fact, E. regnans may be providing a facilitative influence in this case. The information gathered in this study demonstrates that plant functional traits dictate plant responses to ththe biological environment, and that these responses are not solely dependent on the abiotic environment.

En este trabajo se consideró el daño ocasionado por hongos, insectos, animales superiores, malezas, plantas parásitas y agentes abióticos, principalmente sobre cinco especies del género Eucalyptus que tienen gran importancia económica en Chile. Estas corresponden a Eucalyptus camaldulensis, Eucalyptus delegatensis, Eucalyptus globulus, Eucalyptus nitens y Eucalyptus viminalis. Obtenida la información proveniente de esta recopilación bibliográfica será posible aumentar los conocimientos sobre los agentes dañinos que actúan en las plantaciones de Eucalyptus a nivel mundial y que por lo tanto son de interés considerar para la toma de decisiones frente al establecimiento de nuevos cultivos extensivos y medidas correctivas en los ya instalados.

Fire regimes in Australian temperate forests have changed with the area burnt by bushfires having increased due to changing climate extremes every decade for the past 40 years. The Australian Capital Territory (ACT) has been heavily impacted with year-since-last-fire in forests being the shortest of all Australian jurisdictions due to large, intense bushfires during the droughts of 2003 and 2020. The forested landscapes of the ACT are predominantly mountainous and scattered throughout are species and communities which are likely to be disadvantaged by an increase in the frequency of high intensity fire. Examples include alpine bogs, Alpine Ash (Eucalyptus delegatensis) and Mountain Plum Pine (Podocarpus laurencei). Many of these systems were severely burnt in 2003 and 2020. Protection of these species and communities from bushfires is a high priority for conservation, but suppression operations are difficult due to inaccessibility and the danger to firefighters. A potential solution is to use prescribed burning to manipulate fire regimes to reduce risk. In this paper, we describe an approach designed to reduce bushfire risk while optimising land management workloads and total area burnt. The approach has two key components: 1) development of a method for managing landscape bushfire risk in time; and 2) utilisation of landscape flammability mapping to design burn infrastructure to meet ecological objectives. Bushfire risk planning is focused on space, but risk also changes in time with the effects of drought on fuel moisture accumulating and drying over multiple years. This time-scale offers an opportunity to intervene to reduce bushfire risk in fire sensitive ecosystems and influence fire regimes in favour of those ecosystems using prescribed burning. To do this, bushfire planners need to identify ecosystems at risk and develop burns which are to be implemented contingent on agreed climatic triggers. Landscape flammability in mountainous landscapes in southeastern Australia during the autumn prescribed burning season is driven by solar radiation with north faces being drier and much more likely to burn than south faces. This imposes a critical constraint on prescribed burn planning. We analysed conducted an assessment of the feasibility of designing burns to protect alpine bogs, Mountain Plum Pine and Alpine Ash. There appears to be some potential for reducing fuels around alpine bogs and good potential for emhancing protection of Mountain Plum Pine. On the other hand Alpine Ash stands largely occur on southern slopes are do not appear to be easily amenable to fire regime manipulation.