GENERAL MEETING OF THE INSTITUTE HELD AT FORESTS DEPARTMENT,PERTH, ON SATURDAY, 7th DECEMBER, 1940, AT 10 a.m.

This paper discusses the effects of fire on the ability of specially reserved trees of Eucalyptus regnans, E. obliqua, and E, delegatensis (syngigantea) to produce a useful supply of seed for the regeneration of logged areas with a dense understorey of rain forest or wet sclerophyll scrub.

Observations are given on the fire resistance of these eucalypts at different ages and in different environments. The ecological consequences of various combinations of fire resistanos and types of fire are discussed.

The surface of the ground, in the moist cool forests of Tasmania, usually accumulates much raw humus. At the butts of mature eucalypts the humus forms a mound of amorphous, peaty, combustible material at least.several inches, and commonly several feet, deep. The humus can burn only after an unusually dry summer. A fire which consumes it will kill or severely injure all local tree species almost irrespective of bark thickness. Death is due to the killing of the cambium where the humus was burnt in contact with the bark. On the other hand, a fire which consumes only the surface fuels and leaves the humus intact will be much less injurious, especially to trees with thicker bark. Even a complete scorching of the crown is rarely lethal without trunk girdling.

Fire may accelerate the abscission of twigs, leaves, capsules and immature floral parts. The abscission of capsules is accompanied by accelerated seed shed. Immature floral parts do, however, often survive in good numbers provided the twig subtending them survives. Twigs may be killed either from girdling of the tree or by being directly scorched by radiant heat. The leaves and floral parts on killed twigs die, but are not abscissed. Seed shed occurs as soon as the capsules dry out. Seeds inside the capsules on the tree often survive in good numbers.

Because of these findings and because burnt ground becomes relatively unreceptive to eucalypt seed after 1–2 years, owing to excessive weed growth, it is unwise to rely on regeneration from any.seed crop which is not mature at the time of the fire.     

STEM DISTRIBUTIONS IN IRREGULAR FORESTS

A study has been made in a number of blackbutt forests to determine the nature of variation in flowering and seeding characteristics of the species. In all stands the involucre of bracts surrounding the developing blackbutt inflorescence is shed during March and April. In the following year flowering occurs between April and October on Fraser Island and between September and March in most mainland stands, although isolated flowering may occur as early as July. Within an apparently homogeneous section of a blackbutt forest there may be a wide variation in flowering time.

A substantial seed cast with a well-defined peak occurs in the second summer after a heavy flowering on Fraser Island, and about one year after flowering in mainland stands. Where flowering has been light there may be no clearly defined seeding peak, but rather a series of small peaks which are possibly influenced by varying climatic conditions. Within the limited study period a considerable difference in pattern of seed fall between most stands was observed. The percentage of viable seed cast is at a maximum in the first six months following initiation of cast, e.g. 6–8%, and subsequently the viability may fall to a particularly low level, e.g. 1%.

Variation in flowering and seeding is discussed in terms of the widely heterogeneous nature of blackbutt's genetic makeup.     

Problems of regeneration of the mature Eucalyptus regnans F. Muell, (The Big Ash) forest,in the absence of fire at Wallaby Creek,Victoria, Australia

This paper is based on observations on the regeneration of a mature E. regnans forest begun in 1949 and extending over the next 50 years. Any regeneration of E. regnans in the unburnt, mature forest is confronted by a phalanx of obstacles. The formation of large gaps which synchronously involve the overstorey, shrub understorey and fern stratum are an essential prerequisite for establishment, although success may not be assured unless the seedbed has been favourably prepared by mechanical disturbance or fire. In this study, regeneration, which was initiated experimentally by a heavy sowing of seed, scarification of soil, addition of nitrogenous fertilizer, creation of moderately good light conditions and the removal of competition by seedlings of understorey species in the first season, failed completely after 10–11 years even though understorey species which germinated from the soil seed bank continued to thrive.

Processes of seed germination and seedling development are explored in terms of seed harvesting by ants, insect attack, heating and desiccation of the soil surface, mammal browsing, light intensity and dimorphic leaf orientation, mycorrhizal associations, root competition, allelopathic factors, leaf spot fungi and chewing and gall-forming insects. In the tall forest lateral light is considered critical for continued vigour of advanced seedlings with pendulous foliage. Thus, gaps which permit satisfactory development of young seedlings are inadequate for saplings, especially if they are in competition with vigorous regeneration of understorey species. Under light-limiting conditions, survival is severely jeopardized by any factor affecting leaf area or leaf function. It is concluded that while E. regnans appears to be physiologically tolerant of moderate shade it lacks the wider ecological tolerance to it.

Without fire, the regeneration of E. regnans will almost certainly fail in the mature forest unless accompanied by exceptional circumstances. Group tree falls are needed to create regeneration but only on sites incompletely covered by dense ground fern. Synchronous gaps may be needed to disperse herbivore activity in the critical early years. Crown fire eliminates most of the difficulties encountered by E. regnans regeneration by causing mass seedfall, creating a suitable seed bed and by temporarily changing the microclimate, soil moisture regime, soil nutrient status, microbial populations and ant foraging activity. Regeneration may occur in groups following surface fires if large canopy gaps have been produced. In the unlikely event of a very long period without fire, succession to a form of rainforest is likely to occur, although the species may not be eliminated entirely from the area due to the possibility of chance establishment.     

ACCESSION AND DECOMPOSITION OF LITTER IN SPOTTED GUM FORESTS

The accession and decomposition, of litter was studied in spotted gum (Eucalyptus maculata Hook) stands on the south coast of New South Wales during 1963 and 1964.

The average annual litter accession varied from 3,210 lb/ac in a stand of very small saplings, to 6,102 lb/ac in a virgin, overmature stand. The average annual litter accession for spotted gum stands in the study area was estimated to be approximately 5,000 lb/ac.

The components of litter accessions in order of magnitude were: leaves, bark, twigs, and fruiting parts. The greatest accessions occurred in summer. Peak leaf fall preceded peak bark shed which occurred abruptly in the period January-February. The amount of twig fall was relatively small and fairly constant throughout the year.

Litter samples equivalent to 7,000 lb/ac, exposed in three stands for 72 weeks lost 2,300 to 2,900 lb/ac through decomposition. The highest rate of decomposition occurred during the first 36 weeks. The rate of litter decomposition varied between stands with different understoreys; irt stands with Macrozamia and Acacia understoreys the rate was greater than in the stand with practically no understorey.

Rates of litter accession do not appear to be balanced by equivalent rates of decomposition. This situation may result in an accumulation of litter on the forest floor unless other factors such as fire also are involved.     

Infestation of regenerated stands of Karri (Eucalyptus diversicolor) by bullseye borer (Tryphocaria acanthocera,Cerambycidae) in Western Australia

Damage to even-aged regeneration of Karri by the indigenous bullseye borer beetle, first noted in 1967, caused serious concern in 1980 when first thinnings were harvested. The insect has a 2-year-life cycle, 18 months of which are occupied by the woodfeeding lavai stage. The borer occurs within the entire range of Karri forest.

No damage was recorded in fully stocked stands younger than 14 years. Damage tended to be associated with the proximity of even-aged regrowth to old growth forest or non-clearfelled stands, and also with the unsuitability of sites for pure Karri, small coupe size, and drought (average annual rainfall for the period 1967–87 was about 10% less than in the preceding 21 year period (1946–66)). None of the infestations was linked to fire damage.

Thinning regrowth stands of Karri may be a management option for reducing infestation by bullseye borer, but further research on the influence of site factors on Karri physiology and borer ecology is needed before this control measure can be prescribed.     

Responses of foraging ant populations to high-intensity wildfire,salvage logging and natural regeneration processes in Eucalyptus regnans regrowth forest of the Victorian Central Highlands

The effects of high-intensity wildfire plus salvage logging and fire-induced natural regeneration processes on foraging ants (Formicidae) were assessed in multiple-use Eucalyptus regnans (Mountain Ash) regrowth forest approximately 60 km east of Melbourne in the Victorian Central Highlands. The study was based on 35 912 ant specimens, and on 69 493 epigeal non-ant arthropods of 27 taxa, contained in 2,160 pitfall trap samples collected at three sites over a single pre-fire year and two post-fire years.

Twenty ant species of sub-families Dolichoderinae, Formicinae, Myrmeciinae, Myrmicinae and Ponerinae were identified, but only Notoncus spinisquamis, Myrmecia pilosula and Chelaner sculpturatus could be validated. Two species were placed into the newly erected genus OcheteUus (Dolichoderinae), and one species of Myrmicinae could not be identified below sub-family rank. The biology and taxonomy of the majority of these species is uncertain, although the most commonly trapped ant, Prolasius? pallidus, is a recognised seed harvester, and two other species of Prolasius plus C. sculpturatus are suspected seed harvesters. The second most frequently trapped species, Iridomyrmex? foetans, is a carnivore and scavenger. Chelaner sculpturatus was the most frequently trapped among 18 “minor” species.

The rapid replacement of the ecologically complex regrowth forest by young even-aged regeneration of E. regnans through wildfire effects and salvage logging caused a substantial increase in foraging activity of P. pallidus during the first post-fire autumn period, and activity remained high for up to 14 months depending on elevation of the forested landscape. Activity of I. foetans declined immediately after the fire, but eight months later it was significantly higher than “control plot” levels for up to four months. The response of the less frequently trapped “minor” species to the wildfire, logging and regeneration processes remained uncertain because of the low numbers trapped before and after the fire. Prolific regeneration of E. regnans emerged in the burnt forest, suggesting that fire-induced seed fall was sufficiently large and extensive to have caused predator satiation. The implications of this for artificial regeneration programs in E. regnans forest are discussed.     

Effect of Prescribed Burning in a Forest on Wood Characteristics of Jarrah

Wood specimens have been examined which were collected from three positions along the merchantable bole of jarrah (Eucalyptus marginata Sm.) trees growing in Western Australia. These trees had been subjected to a series of two experimental fires at either of two intensities in either spring or autumn. The more intense fire caused crown and trunk damage and resulted in kino vein formation. If such burning took place in autumn, loss of radial growth resulted. The less intense fire treatment did not result in external damage. Minor disturbances to the density profiles in the first year after the fire were the only observed effects on characteristics of the wood.     

Extreme wildfire behaviour in 3-year-old fuels in a Western Australian mixed Eucalyptus forest

This paper describes the behaviour of an intense wildfire which burnt through three-year-old fuels in open forest of jarrah (Eucalyptus marginata), marri (E. calophylla) and karri (E. diversicolor) near Manjimup, W.A. The fire occurred during very dry fuel conditions which resulted from record high air temperatures (maximum 43.5°C) following a rainless period of twenty eight days. Fire danger at the time was Extreme, with a peak McArthur Forest Fire Danger Index of 65. The fire crowned extensively in mixed-aged jarrah/marri stands, and it is proposed that crown fire initiation was facilitated by the substantial component of sapling and pole-sized regrowth which provided a vertically continuous fuel structure. Concentrated spotting occurred up to 2km downwind of the fire, and an isolated spot fire developed 8km away. During an initial run under north-westerly winds the fire travelled 2.2km with an average forward rate of spread of 1300m/h, which is somewhat faster than predicted by either the Western Australian Forest Fire Behaviour Tables or the McArthur Forest Fire Danger Meter. The relatively low fuel loads in the area appear to have assisted in the rapid containment of the fire once burning conditions moderated.     

PLANT SUCCESSION AND PINE REGENERATION

On small areas of clear felled Pinus radiata stands at Mount Stromlo in the A.C.T. the plant communities have been examined by means of a permanent, charted sample plot and by Raunkiaer's percentage frequency method. The relatively stable grassland subclimax communities which existed before the planting of the pine stands are described and the effect of the pines upon them and the resulting pine dominated community discussed. The succession of communities in time which follows clear felling of a pine stand is found to be, firstly a community dominated by clovers, followed by one of tall-growing annuals and finally passing to one dominated by perennial grasses. Pinus radiata regeneration is considered in relation to this succession and the conclusion drawn that, since Pinus radiata cannot regenerate amongst perennial grasses, after about four years the site of a former pine stand will no longer be suitable for any natural regeneration. If natural regeneration fails for a couple of seasons while the site is still suitable, steps could be taken to prevent further loss of time and artificially regenerate the area.

It is noted that Pinus ponderosa var. scopulorum, unlike Pinus radiata, is able to regenerate amongst the perennial grasses.

It is suggested that information of value in relation to the fundamentals of biotic succession may be derived from further study of this sere.     

Moisture content measurement on Eucalyptus seed for storage

Seed moisture content may significantly affect the storage life of both agricultural and forest species. Seed store managers therefore need an easy and reliable method for routinely checking moisture contents. A robust, portable, easy- to-use electrical seed moisture meter, the Protimeter Grainmini V, was evaluated on samples of Eucalyptus globulus, E. pulchella and E. obliqua seed. Meter readings were well correlated with gravimetric moisture contents ranging from 4.7% to 24.3% of oven dry weight. Relative humidity readings were also made on the equilibrium atmosphere within sealed bags of seed to see whether it might be feasible to derive seed moisture indirectly via relative humidity.

For E. globulus, the fertile seed had gravimetric moisture contents several percent lower than the associated chaff, which normally comprises the bulk of a stored Eucalyptus seed lot. Equations were derived to define the relationship between the overall moisture content and that of the fertile seed, and the way this relationship is affected by the fertile seed/chaff ratio. Fertile seed also gave a higher meter reading than chaff at the same gravimetric moisture content. These effects were much less marked with smaller-seeded eucalypts.

These findings have been incorporated in calibration tables for the electrical meter, which is now used by Forestry Tasmania to screen all Eucalyptus seed prior to and during storage. Results should be generally accurate to within about ± 1 % of oven dry weight.

The concept of deriving seed moisture content indirectly through the equilibrium humidity of the seed atmosphere seems sound in principle but is impractical for this purpose at its present stage of development.     

THE EFFECT OF CHANGING MOISTURE CONTENT ON THE GERMINATION OF SLASH PINE SEED

The germination characteristics and seed moisture content of slash pine seed which has been immersed in water and then dried in the air for various periods have been examined after each of the soaking and drying combinations.

The moisture content of seed immersed in water rose rapidly initially but would take more than 7 days to reach a maximum of about 50% above the seeds' oven dry weight.

The moisture content of moist seed left to dry under room conditions fell rapidly to the equilibrium moisture content of 10–14%; a consistent fall of 17% per 24 hours was recorded.

The seed germination rate and germinative capacity rose with increasing moisture content, but no direct relationship between moisture content and germination could be found.

Pre-soaked seed which was left to dry showed a decrease in germination rate and germinative, capacity, but this decrease is not directly related to the time elapsed before conditions again favour germination. Minimum germination values appeared to be related to the final drop in seed moisture content to the equilibrium, and germination values increased where the seed was held for longer than the time necessary to reach equilibrium moisture content.

The moisture content of seed soaked for up to 80 hours might fall to the equilibrium value within 2–3 days, but soaked seed held in the open for 15 days germinated faster and more completely than unsoaked seed held in the open for a similar period.

It was only under the one combination of conditions in which seed was soaked for 50 hours and held to dry for about 10 days, that the rate and degree of germination was markedly less than that of untreated seed.     

Slash burning—its implications for 20-year height growth of eucalypt regeneration in Tasmania

Height data to 20 years are presented for a study previously reported by Lockett and Candy (1984) on the effects of slash-burning on growth rates of eucalypt regeneration established following clear-falling. The study covers a range of forest types on five sites throughout Tasmania with rainfalls ranging from 800mm to 1800mm.

On the two driest sites, the initial conclusion that slash burning had no significant impact on height growth has been confirmed by subsequent measurements. On the three wetter sites, there was a consistent trend which suggests that slash-burning caused growth rates to be more than doubled in the third year post-burn. This effect progressively declined and finally disappeared between years ten and fifteen. The net result of burning would be a shortening of the rotation by a maximum of five years, or less where natural regeneration is already established, or can be established earlier in the absence of a slash-burn.

Operationally, the decision whether to burn or not will involve balancing these growth effects against the stocking, size and potential vigour of new natural regeneration or older advance growth and the desirability of preserving it. This may require consideration of how difficult it is to establish regeneration on the site and how much the risk of wildfire will be increased if slash is left unburnt.     

HIGHER FORESTRY EDUCATION IN AUSTRALIA

The results of three field trials which were established in 1976 to determine the feasibility of increasing wood production of Pinus radiata by fertilisation of thinned stands are described after four years of growth following the fertilisation treatments. The stands of about 20 years of age were producing an average of 14 m³ ha^?1 stem-wood per year.

The extra volume of wood growth resulting from fertilisation averaged 4.2 m³ ha^?1 a¹ for all sites, and 5.9 m³ ha^?1 a^?1 for the two most responsive sites, the latter being 37% over that obtained from unfertilised stands. Fifty per cent of the extra volume was added to the largest one-third of trees in the stands. A dominant tree of diameter (bhob) 27.0 cm in 1976 became 30.7 cm in 1980 if unfertilised and 32.8 cm if fertilised, an increase of 2.1 cm.

The responses obtained were inversely proportional to both the relative growth rates of unfertilised stands following thinning, and to the nitrogen concentration in the foliage of unfertilised trees measured in the year following fertilisation. Some soil/plant relationships have been examined for nitrogen, phosphorus, potassium and sulphur.

Fertilisation at this age appeared to at least ‘break-even’ if costs were amortised at an interest rate of 6%. However, fertilisation may also be a useful means of increasing yields at relatively short notice and allow increased flexibility in harvesting and other forest operations.     

A form diagram to optimise pruning schedules for eucalypt clear-wood production

Branch pruning is necessary to produce high-value wood products from eucalypt plantations. Four requirements of an effective and efficient pruning regime for clear-wood production are to (a) restrict the pruned-stem diameter to a specified maximum, (b) ensure only green branches are pruned, (c) remove a proportion of the green crown that allows for continued competitiveness of the pruned trees and (d) minimise the number of pruning interventions. In this paper, we present a pruning decision support tool that diagrammatically combines results from growing stands and crown reduction trials. Elements depicting the pruning schedule, target maximum pruned diameter (PD_max), lower height of the green crown (GC_LH) and target retained proportion of the green crown (GC_RP) are overlaid onto a set of stem-taper curves. The form diagram was demonstrated using data from two adjacent commercial plantations of Eucalyptus pellita (‘Caravan Hill’ and ‘Fishtail’), established in the same planting season, for solid-wood production in northern Queensland, Australia. We fitted a cubic tree taper model that described 89% of the variation in stem diameter at a given height. PD_max was set at 12 cm and GC_RP was set at 50%. Pruned height was set at 6 m assuming two lifts.

Site differences in E. pellita growth, slenderness and green-crown height resulted in different optimum pruning schedules even on adjacent holdings. Within-stand heterogeneity in slenderness and green-crown height contributed further to the complexity of pruning scheduling. Our results suggest that it would have been necessary to complete the Fishtail site pruning program at the commencement of the second dry season after planting to ensure that the pruned height was always greater than GC_LH. On the other hand, the first pruning lift could be conducted at the Caravan Hill site at the same time that the second lift was being completed at Fishtail. Management options that increase the height growth in the first year, promote live crown retention and increase within-stand homogeneity will improve the effectiveness of fixed-lift pruning for eucalypt clear-wood production.     

Differences between wildfire and clearfelling on the structure of montane ash forests of Victoria and their implications for fauna dependent on tree hollows

Some differences between the effects of clearfelling and wildfire on the vegetation structure of montane ash forests in the Central Highlands of Victoria are reported. The significance of these differences is considered in terms of their possible impacts on wildlife, particularly those species which are dependent on hollows in trees.

Distinct differences between the vegetation of montane ash forests which have been clearfelled and those burnt by wildfire include: –(1) the range in ages of trees in a stand, and, (2) the spatial pattern, abundance and longevity of hollow-bearing trees. In stands burnt by wildfire, the longevity of hollow-bearing trees may be more than 50 years and several forms of such trees can be present. These trees are removed from clearfelled forest. In unlogged stands and stands regenerating from selective logging the spacing of hollow-bearing trees was typically regular in distribution. In contrast, the spatial distribution of hollow-bearing trees was clustered in stands which had regenerated after clearfelling.

These differences may have a significant detrimental impact on wildlife and lead to a reduction in the abundance of some vertebrates in a given area of forest. Species such as arboreal marsupials, owls and cockatoos, which are reliant on a hollow-bearing trees for shelter and breeding, will probably be those most affected.     

Crown Recovery of Eucalyptus dives Following Wildfire

The restoration of crowns of 5–7 m tall trees of E. dives of coppice origin was studied after a wildfire on October 1, 1971, near Captains Flat, N.S.W. Unburned plants were compared with those which had their crowns completely scorched but not burned and those which had their leaves completely burned off by crown fire. All trees survived. Approximately 50 per cent of the height of crown-burned trees was killed and 30 per cent in the case of crown-scorched trees. While these results were significantly different most measurements of crown recovery were similar for these two classes of fire-affected plants. Leaf weight was restored within 8 months of the fire. The clumped pattern of epicormic shoots emergent along surviving trunks soon after the fire was replaced by that of the normal branching pattern less than three years later.     

AN INVESTIGATION OF CONE AND SEED MATURITY OF SLASH PINE IN SOUTHERN QUEENSLAND

Cones and seeds of slash pine (Pinus elliottii var. elliottii Engl.) collected at fortnightly intervals from mid-January (nine weeks prior to natural seed shed) to mid-March were given different storage treatments which varied with time and the conditions of temperature, moisture and aeration with the object of maturing the seed.

Storage of immature seed extracted immediately after cone collection had little effect on germination. Storage of cones in the shade with free air circulation successfully matured some seed from early collections, while storage in damp hessian or cellophane within damp hessian was also successful. Germination percentages of seed tended to maximize after four to six weeks of cone storage and then decline. Germinability increased the nearer that the collection was made to the time of natural seed fall, but showed no improvement over a period of nearly a month prior to this taking place.

Embryological investigations showed that embryo length and degree of morphological development were not satisfactory guides to germinability. Embryos required a period after completion of morphological development to reach physiological maturity. This period varied according to the storage treatment imposed.

Cones which were collected in January were not opened by any of the opening treatments applied for this purpose, whereas those collected in early February were successfully opened by an alternating drying and wetting technique. Most cones collected in late February and mid-March were opened by oven drying at 115°F.

The investigation indicated that some between-tree variation existed in the phenology of seeding patterns in slash pine. Some suggestions for future work on the general problem of cone and seed maturation in this species are outlined.     

Book Review

The effects of three prescribed low intensity fires varying from means of 80 to 209 kWm^?1 within six years on invertebrates in litter/upper soil were assessed. The 8.6 year study was based on 88 934 arthropod specimens, representing 35 ordinal or lower level taxa contained in 3520 pitfall trap samples from a site burnt three times in spring and an unburnt control site within a 30.7 ha area.

The three fires had no discernible effect on total taxa, total non-insects, Araneae (spiders), Acarina (mites), Collembola (springtails), total insects and Formicidae (ants), although activity of the Coleoptera (beetles) decreased significantly after the second and third fires while that of the Diptera (flies) increased over the same period. However, as Coleoptera and Diptera activity on the unburnt control site decreased and increased respectively over the same period, it is uncertain whether the changes in activity were due to the fires or other non fire-related environmental factors. Futhermore, these changes in activity resulted from one or two of the spring fires only, and not all three, further questioning whether the fires were the contributing causal factors.

Three prescribed low-intensity fires in spring appear therefore, not to impact adversely on the activity of major forest litter arthropod groups, although the situation of the Coleoptera and Diptera is less clear due to similar activity on the unburnt control site in both cases. This therefore suggests that any fuel reduction burning in spring be conducted at intervals of not less than three years in order to minimize any impact on litter arthropods. Where a period of drought has occurred, burning should be delayed until the drought period has ended.