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Fuel moisture is a key driver of forest flammability as it influences ignition likelihood, fire intensity and resultant fire severity. Changes to forest canopy cover following disturbances like wildfire or logging may alter forest flammability by changing the microclimatic conditions that influence fine fuel moisture. Wet forests dominated by Mountain Ash (Eucalyptus regnans) are highly valued for their flora and fauna, timber, carbon and water. Wildfires are an important part of the lifecycle of these forests, but too frequent fire can threaten post-fire regeneration. With large tracts of Mountain Ash forest recovering from recent wildfires (in 2009 and 1983) there is a need to understand the mechanisms driving flammability in these forests, particularly as the forest structure changes following fire. This study sought to understand the effects of fire history on the flammability of Mountain Ash forests by specifically considering fuel moisture for different times since fire and fire severities. We measured canopy cover (plant area index) and fuel moisture within 8 forest sites last burnt between 7 and 200 years ago by wildfires of low or high severity. Fuel moisture and fuel availability (i.e. number of days when fine fuels are dry enough to ignite and sustain spreading fire) were strongly associated with canopy cover; with denser canopied forests having higher fuel moisture. The largest differences in canopy cover occurred between the recently burnt high and low severity forests. For the longer-unburnt forests there were no systematic differences evident in canopy cover with time since fire or fire severity. The fuel moisture was higher and fuels only available to burn on one day in the forest recently burnt by high severity fire (in association with a dense canopy). In contrast, fuels were drier and available to burn on 238 days in the forest recently burnt by low severity fire (in association with a sparser canopy). For the longer-unburnt forests (33 or more years since fire) there were no clear trends between fuel moisture and time since fire and fire severity suggesting that fires do not have a lasting impact on fuel moisture within these wet forests. Overall, this study shows that wildfires have immediate impacts on fuel moisture in Mountain Ash forests but as the time since fire increases, moisture appears to be more a function of canopy properties than fire history.

We undertook a study to test the hypothesis that fertiliser application would moderate the effects of insect herbivory on stem growth of plantation-grown Eucalyptus globulus Labill. Three-year-old E. globulus with damage from the Eucalypt weevil ( Gonipterus scutellatus ) ranging from 0–50% loss of total crown leaf area were fertilised with either nitrogen (N), phosphorus (P) or the combination of N + P. Stem growth and crown condition were monitored for 12 months. Applications of N or N + P increased diameter and height increment for both treatments, suggesting nutrient limitations at the site. In the absence of fertiliser, diameter and height increment were significantly reduced when defoliation was more than 10%. The application of N + P or N alone increased diameter increment in all defoliation classes to at least the level of unfertilised trees with minimal defoliation. Application of P did not. While there was an overall improvement in crown condition over the experimental period, trees in the N only treatment displayed a greater improvement in crown condition, and less trees per plot had poorer crown condition, than did trees in the other treatments. It was concluded that fertilising with N offers a management tool to eucalypt growers concerned with loss of productivity following insect defoliation.

Defoliation from herbivores can reduce growth of affected plants, and this has been demonstrated for plantation-grown Eucalyptus globulus. We undertook a field study to examine: (1) the influence of severity, pattern and frequency of defoliation on E. globulus stem growth, (2) whether fertiliser application influences growth responses to defoliation and (3) whether rate or timing of fertiliser application is important in determining growth responses. Two rates of nitrogen (N) (100 or 300 kg ha−1) were applied either pre- or post-defoliation or both. Defoliation treatments examined the effects of pattern, frequency and severity of defoliation on growth. In the absence of fertiliser, removal of 25% of leaf area from throughout the crown reduced diameter and height increment over the following 20 months. Removal of all leaf area from the upper 50% of crown had a much more dramatic effect on stem growth than did removal of all leaf area from the lower 50% of crown. More frequent defoliation increased the effect of defoliation on stem growth, and there was more of an effect following defoliation of the upper rather than lower crown. While there was no fertiliser response in undefoliated trees at the site, pre-defoliation fertiliser application maintained diameter and height increment of defoliated trees at a level similar to that of undefoliated trees. The growth response to fertiliser following defoliation was greater with pre- than post-defoliation applications of N, although there was still a significant response to post-defoliation applications. While foliar N content increased with rate of N application in undefoliated trees, defoliation generally reduced foliar N content and total phenolics. It was concluded that fertilising with N, even on sites with no discernible N deficiency, is a potential management tool for dealing with defoliation events. Management implications of the results are discussed.

The effect of a high rate of fertiliser addition, (900 kg ha −1 nitrogen (N):150 kg ha −1 phosphorus (P)) on pruning associated decay was investigated at two N and P deficient sites in Tasmania, Australia. Decay infections from pruned stubs were found to be more common in trees that received additions of fertiliser N and P, but fertiliser addition was not found to have an effect on basic density, lignin or the concentrations of extractives. Crown depth, and branch size were greater, and kino production reduced on trees that received fertiliser N and P. The incidence of decay infections in the pruned branch stubs increased with the frequency of living and large branches. Hence, improved tree nutrition increased the longevity and size of branches, thereby leading to an increased incidence of decay infections.

Low nitrogen (N) availability commonly limits the growth of Eucalyptus nitens plantations on ex-forest sites in Tasmania, Australia. We summarise here a decade of mechanistic and empirical research that has improved the basis for N management of these plantations. Twenty-two fertiliser experiments were used to define relationships between tree growth and methods of N fertilisation, i.e. timing, frequency, form, rate and placement. Pools and fluxes of mineral N were monitored at five sites. Potential deficiencies of N between planting and 10 years of age were indicated by the concentrations of soil NH4, NO3, total N and total phosphorus (P). Appropriate timing of N fertilisation depended on when N demand started to exceed supply from soil reserves, and was indicated by soil total N. Plantations on low-N sites experienced N deficiency during the first few years of growth, but others experienced it later or not at all. High cumulative rates of N fertilisation (at least 500 kg N ha−1) were needed to maximise growth at many sites, but there is no evidence to suggest that any individual application in excess of 200 kg N ha−1 is warranted. Hence, multiple applications will be needed to maximise growth. Urea was the preferred form of N, because it was relatively cheap and at least as effective as other N forms. Limiting N application to the crown drip line of 6-year-old trees with small crowns did not increase growth compared to a totally broadcast application. Soil N availability increased for 1–2 years following most N-fertiliser applications. Tree growth rates increased significantly for the same period followed by several years of less significant responses during which re-applications promoted a more sustained response in growth. This research has fostered an increase in the use of N fertilisers to increase productivity, and it should improve the basis for evaluating the economics of options for N fertilisation. Although applications of N fertilisers at rates up to 200 kg N ha−1 and at intervals of several years are unlikely to be a threat to water quality, especially if urea is used, research is needed to determine the environmental risks associated with long-term and higher intensity uses.

Leaf area index (LAI) is a key driver of water and nutrient use, carbon balance, and the rate of growth of plantation forests, but these interactions can be environment-dependent. Our aim was to determine the relationship between LAI and stem growth in four 5–8-year-old Eucalyptus nitens plantations and its dependence on site and fertilization. Fertilizers were applied at various intervals between planting and age 6 years at cumulative rates that ranged from 0 to 1600 kg N ha−1 and 0 to 700 kg P ha−1. Stem growth and LAI were monitored for 2 years. Values of LAI ranged from 1.4 to 9.6, and temporal variations in LAI were small. Fertilization increased LAI by up to 3.1 units. There was a strong relationship across all sites and treatments between initial LAI and growth, and predictions using LAI were more precise than those using basal area as the independent variable.