Impacts of commercial thinning on stand demography, fuel loads, microclimate and fire behaviour in Eucalyptus delegatensis forest in eastern Tasmania

Fire history and understorey vegetation: Water and nutrient relations of Eucalyptus gomphocephala and E. delegatensis overstorey trees

Impact of mechanical thinning on forest carbon, fuel hazard and simulated fire behaviour in Eucalyptus delegatensis forest of south-eastern Australia

Chemical analysis of the total sugar and total nitrogen content of Acacia dealbata, Acacia obliquinervia and Acacia frigescens gum exudate was completed. These trees were located within stands of 53 year old Mountain Ash, Eucalyptus regnans and Alpine Ash, Eucalyptus delegatensis forest in the Central Highlands of Victoria, southeastern Australia. Values for sugar content ranged from 24 to 68% per sample. Gum samples that were collected in E. regnans forests had a significantly lower (P<0.05) sugar content than those from stands dominated by E. delegatensis. Statistical analyses using Scheffe's S‐test indicated that there was a significant difference in the sugar content of gums between A. dealbata and A. frigescens but not between A. dealbata and A. obliquinervia or A. obliquinervia and A. frigescens. Values for the nitrogen content of Acacia gum varied from 0.2 to 0.7% per sample. Statistical analyses revealed that nitrogen content was significantly influenced (P<0.05) by a combination of three interacting factors: (i) Acacia species; (ii) tree diameter; and (iii) forest type. Therefore, the findings of this study indicate that the sugar and nitrogen content of Acacia gum may vary between forest types and tree species. The gum of Acacia species is an important source of food for several species of arboreal marsupials, and differences in sugar and nitrogen content could be a factor potentially influencing the distribution and abundance of these animals.

This paper presents equations for fuel load and fuel hazard rating (FHR) models based on the time since last fire for dry eucalypt forests in eastern Tasmania. The fuel load equations predict the load of the surface/near-surface and elevated fine fuel. The FHR equations predict the surface, near-surface, combined surface and near-surface, bark, and overall FHR. The utility of the “Overall fuel hazard assessment guide” from Victoria, Australia, is assessed for Tasmanian dry eucalypt forests: we conclude that, when fuel strata components are weighted according to their influence on fire behaviour, the Victorian guide provides a rapid, robust, and effective methodology for estimating FHR. The equations in this paper will be used for operational planning and on-the-ground performing of hazard reduction burning, prediction of fire behaviour for fire risk assessments and bushfire control, and providing inputs into the new Australian Fire Danger Rating System.

The late Quaternary vegetation communities of the south‐central highlands of Victoria are reconstructed from analyses of pollen and charcoal, and associated environmental conditions derived from the record of Nothofagus cunninghamii and alpine and sclerophyll taxa preserved in four subalpine Sphagnum bogs. The highest site occurs amid Eucalyptus paudflora woodland, the two intermediate sites are surrounded by Eucalyptus delegatensis forest and the lowest by a mixed forest of E. delegatensis/Eucalyptus regnans. Small pockets of N. cunninghamii occur within the eucalypt forests, and in close proximity to all four sites. Around 32 000 BP the vegetation consisted of a mosaic of alpine feldmark and herbfield, with small scattered groves of Nothofagus and Eucalyptus well below 1100m. Summer temperatures were probably 5°C lower than present with lowest values, probably 7° to 8°C below present, possibly between 17 000 and 13 500 BP, at which time alpine communities reached their greatest extent and much of the Central Highlands was treeless. After ca 13 500 BP herbaceous alpine taxa disappeared and there was an associated movement upslope of Nothofagus and tall open forest taxa to their maximum post‐glacial extent, as temperatures and effective precipitation increased, ca 6000 BP. The retraction of cool temperate rainforest and wet sclerophyll or tall open forest towards present day values indicates lower effective precipitation, generally rising temperatures and increased fire hazard. More recently, European activities have increased the stress on the remaining forests. The study of four sites has demonstrated die importance of analysing a number of sites within a given area in order to overcome the limitations imposed by sites which were sub‐optimal due to one or more factors including poor preservation, problems of dating, variable sedimentation rates, and the influence of streams which flow close to all sites. While die local environment varies between sites, and some vegetation changes are successional, this study shows that the local records complement one another, to some extent reinforcing die regional picture of vegetation and environmental change.

The objective of this study was to identify attributes of the understorey vegetation, soil root biomass, soil chemistry and microbial community that may be associated with tree decline in high altitude eucalypt forests in Tasmania. The sites studied were in healthy eucalypt forest, forest in decline and forest containing dead eucalypts dominated by rainforest, in north‐east (Eucalyptus delegatensis forest) and in north‐west (Eucalyptus coccifera forest) Tasmania. In both regions bare ground, rock and shrubby species were associated with healthy sites whereas decline sites were associated with moss and a tall understorey with a high percentage cover of rainforest species. Healthy sites had low root biomass in the top 10 cm of the soil profile relative to decline and rainforest sites. Seedlings of high altitude species were grown in rainforest soil (0.314% N and 0.060% P) and healthy eucalypt soil (0.253% N and 0.018% P). The four eucalypt species studied had similar root to shoot ratio in the two soils, but the rainforest species, Nothofagus cunninghamii and Leptospermum lanigerum, had higher root to shoot ratio in the healthy eucalypt than in the rainforest soil. We produced three soil filtrates: (i) fungi and bacteria present; (ii) bacteria only present and; and (iii) sterile, from healthy, decline and rainforest sites in north‐east and in north‐west Tasmania and used linseed as a germination bioassay. Filtrates from the north‐east decline and rainforest sites induced a significantly greater dysplastic germination response than healthy sites in (i) and (ii) filtrates, but this was not found in filtrates from sites in the north‐west. We conclude that while the development of a rainforest understorey and elevated soil root biomass in the long absence of fire is generally associated with high altitude eucalypt decline, altered bacterial and/or chemical attributes of soil are not always associated with high altitude eucalypt decline.

Soil–atmosphere greenhouse gas exchange in a cool, temperate Eucalyptus delegatensis forest in south-eastern Australia

Fire ecology for the 21st century: Conserving biodiversity in the age of megafire

Variation in Eucalyptus delegatensis post-fire recovery strategies: The Tasmanian subspecies is a resprouter whereas the mainland Australian subspecies is an obligate seeder

Summary Poor early establishment and growth of regeneration following clearfelling of highland dry Eucalptus delegatensis forests in Tasmania in the 1970s led to the development of alternative practices. Shelterwood retention, shelterwood removal, potential sawlog retention and advance growth retention systems were developed and implemented by forest owners as preferable alternatives to clearfelling in most instances. Less than optimal outcomes following partial harvesting led to the development of formal monitoring procedures. These procedures assess the pre-harvesting forest structure, guide development of the harvesting prescription, follow the course of harvesting, return information on progress to the harvesting contractor, and allow for continuous improvement of operations. Together they ultimately provide improved outcomes for the forest grower. The paper discusses the development of uneven-aged management and describes the processes used to develop and monitor the outcomes.

Factors influencing the occurrence of mammals in retained linear strips (wildlife corridors) and contiguous stands of montane ash forest in the Central Highlands of Victoria, southeastern Australia

Ground and satellite-based assessments of wet eucalypt forest survival and regeneration for predicting long-term hydrological responses to a large wildfire

Forests that regenerate exclusively from seed following high‐severity fire are particularly vulnerable to local extinction if fire frequency leaves insufficient time for regenerating plants to reach sexual maturity. We evaluate the relative importance of extrinsic (such as fire weather and climate cycles) and intrinsic (such as proneness to fire due to stand age and structural development) factors in driving the decline of obligate seeder forests. We illustrate this using obligate seeding alpine ash (Eucalyptus delegatensis) forests in the montane regions of Victoria, Australia, that were burnt by megafires in 2003 (142,256 ha) or 2007 (79,902 ha), including some twice‐burnt areas (11,599 ha). Geospatial analyses showed only a small effect of stand age on the remote sensing estimates of crown defoliation, but a substantial effect of forest fire weather, as measured by forest fire danger index (FFDI). Analysis of meteorological data over the last century showed that 5‐year increases in FFDI precede cycle major fires in the E. delegatensis forests. Such strong extrinsic climate/weather driving of high‐severity fires is consistent with the ‘interval squeeze model’ that postulates the vulnerability of obligate seeder forests to landscape‐scale demographic collapse in response to worsening fire weather under climate change.

Summary Past selective loggings in high altitude multi-aged Eucalyptus delegatensis forests inefficiently utilised the timber resource. However, the small forest clearings created by selective logging are stocked by healthy regrowth that established following wildfire. Pulpwood markets now enable more efficient logging through integrated pulpwood-sawlog operations. The regeneration on some sites following clearfelling has been severely damaged by frost. Canopy cover provides a barrier to nocturnal radiation loss, thus preventing severe frosts. Therefore shelterwoods are currently being explored as an alternative to canopy removal by clearfelling. Shelterwoods and selective logging systems are essentially similar in terms of forest regeneration practices but differ according to the resultant age structure of the regrowth forest. With the former system, once the even- aged regrowth is considered relatively immune from frost damage the overwood is cut. The decision to use either selective or shelterwood syst...

Summary Partial logging was introduced to Eucalyptus delegatensis forests at altitudes over 600 m to reduce the incidence of high altitude growth check. Subsequently it has been used for a number of other management reasons. Experiments showed that whilst the initial stocking of regeneration increased with basal area of stems retained, later aged stocking and growth of regeneration could be severely depressed by the retention of basal area in excess of 12 mha−1. Where shelterwoods are prescribed, the optimum level of basal area that should be retained will vary according to the annual rainfall of the site, but in general basal area should be reduced to the lowest level capable of providing the requisite protection and ensure full stocking. This figure can be expected to vary between 12 and 16 m2ha−1. These results have been incorporated into operational prescriptions for this forest type.