The interpretation of key life history attributes is a useful means of highlighting the potential threats that individual plant taxa or groups of taxa may face. In this review, particular life history attributes are used to indicate possible or likely sensitivity to the impacts of a range of natural and human-induced disturbances which occur in forest areas.
The major constraint on this review is the lack of detailed information on ecological attributes for most native species.
Appendix F presents a list of the species used in this review, comprising mainly rare or threatened species, but including 22 species which are not rare or threatened but which represent a range of taxonomic groups and life-forms. Coded spreadsheets for all of the species considered in this review has not been reproduced in this report.
The link between a disturbance and any decline or extinction, either locally or globally, of particular species, is best understood by considering the separate components and evaluating their relationship. In this review, examples of species most likely to be (but not necessarily) threatened by a disturbance are identified on the basis of ecological attributes which predispose them to a particular potentially threatening process which is associated with a disturbance.
The strength of the association between disturbances and potentially threatening processes is variable. For simplicity, these relationships are classed as strong, weak or non-existent, based on the scientific literature and expert opinion. A strong association is one where the potentially threatening process is usually or always associated with the disturbance, while a weak association is one where the potentially threatening process is sometimes associated with the disturbance.
A number of other categories of disturbance have not been considered in this review, either because they do not have a significant impact on native flora or because they constitute variations on disturbances which have been considered. For example, fire suppression activities can include the clearing of native vegetation for vehicle or helicopter access, the use of back-burning to retard the intensity and rate of advance of the fire front, and the use of fire retardant chemicals. Rather than duplicate information, the component activities of fire suppression are dealt with under clearing, planned fire and pollution.
Each disturbance has been evaluated to determine the extent of its occurrence within the Central Highlands, the potentially threatening processes which are associated with it, the strength of that association, the overall significance of the threat to native flora in the Central Highlands, the ecological, life-history and life-form attributes which might predispose a taxon to significant negative impacts, and examples of the taxa that might therefore be susceptible to the disturbance.
Management systems, including policies and processes, for the amelioration of the adverse biodiversity impacts of the disturbance are also reviewed and summarised. The adequacy of existing information on the extent and impacts of the disturbance is also reviewed. The results are presented as text with each disturbance considered in turn.
Species attributes: Data were obtained from the literature when available or was estimated by a botanical consultant based on previous experience.
Habitat attributes: Quadrat data stored in the NRE Flora Information System was analysed to determine the Ecological Vegetation Classes (EVC) where the species were most commonly found. For each species up to 10 randomly selected quadrats were chosen and the EVC for each quadrat established by comparative analysis. In total, over 700 quadrats were categorised. On average a widespread species had 169 quadrats in which they occurred and categorised (6% of all the point records for that species) while a rare or threatened plant had 8 quadrats in which they occurred and categorised (32% of all the point records for that species). This information was summarised for each species.
Soil moisture, soil fertility and landform data was extracted from the literature, NRE databases or was estimated by the consultant based on previous experience.
Disturbance categories: Disturbance categories for a species was based on published literature, NRE databases or was estimated by the consultant based on previous experience.
Clearing of native vegetation
Clearing of native vegetation occurs as part of agricultural, industrial, urban, utilities or tourism development, or mining or extractive industry development. Clearing of native vegetation is not occurring at a significant rate within the Central Highlands, although the loss of vegetation on private land, particularly on the outskirts of Melbourne, is significant in some local areas. Permanent clearing on public land is confined to very small areas mainly for the development of recreation facilities or as part of the installation of infrastructure, such as radio telephone towers. Historically, however, clearing of native vegetation has been the single most important and widespread cause of decline, local extinction and regional extinction of species and communities in the Central Highlands.
Potentially threatening processes associated with clearing of native vegetation include the total loss or severe modification of habitat. While this is strongly associated with clearing of native vegetation; its overall significance is considered moderate, despite being high in some areas/environments, given the localised nature of clearing. Other potentially threatening processes associated with clearing of native vegetation include the direct damage or loss of individuals, which is strongly associated with this disturbance, but which is considered to be of low significance overall.
No specific attributes predispose a taxon to threat from clearing of native vegetation as most if not all native plants are susceptible. Few if any native plants can survive broadscale clearance of vegetation where the result is conversion of the land to intensive human use for urban, industrial, tourism or other purposes. However, clearing for agriculture does not always eliminate all native species. While the conversion of native vegetation to unimproved pasture usually involves the removal of trees and shrubs, many native herbs survive and in some cases prosper. However, as only vigorous reproducers (ie. weedy species) can tolerate such disturbance, its impacts are likely to be greatest on species with relatively low reproductive output.
The clearing of native vegetation on public land requires Ministerial or Departmental approval. Planning permission may also be required in some cases. Major developments, including many mining and extractive industry developments, are the subject of Environmental Effects Statements, in which the impacts on native flora are usually considered. The taking of protected flora associated with clearing requires authorisation under the Flora and Fauna Guarantee Act. The clearing of native vegetation on private land requires planning permission from the local planning authority in most cases. For parcels of land greater than 10ha in area, NRE approval is required.
In cases such as mining and extractive industry activities where rehabilitation is carried out following utilisation of the resources concerned, significantly less long term loss of biodiversity may occur, depending on the effectiveness of the rehabilitation.
Since the introduction of planning restrictions on the clearing of native vegetation on private land in 1989, the rate of vegetation loss has decreased tenfold in Victoria. However, it is possible that applications to clear will increase in coming years, including proposals for plantation establishment.
Information on the rate and location of major vegetation clearing is generally good. Record keeping for cases requiring formal planning approval is good, while the use of satellite imagery allows for detailed comparison between current and past extent of native vegetation. Few if any detailed studies of the impact of clearing on native flora have been undertaken. The greatest need for research is in the area of the impact of vegetation fragmentation on the reproductive biology of key taxa, and on the long term management of remnants.
The following discussion of timber harvesting refers to the clearfall harvesting system most commonly employed in the Central Highlands, including the felling, snigging and loading of logs, and the preparation of the coupe for regeneration burning, which is discussed separately in the “Planned Fire” section. In some cases, coupes are mechanically disturbed rather than burnt.
Clearfelling is the timber harvesting system most commonly used in the Central Highlands. It involves the felling of all canopy trees except for designated habitat and seed trees. In practice, many non-eucalypt trees and shrubs in the understorey are also felled to facilitate harvesting and improve safety on site. Once felled, the heads (upper trunk and smaller branches) are removed from the logs and the logs are towed via snig tracks to a landing where they are graded and loaded onto trucks. Following the completion of harvesting, log landings are ripped to reduce soil compaction. The heads plus any unwanted logs and non target species, are usually bulldozed into windrows or heaps in preparation for the regeneration burn.
Timber harvesting is widespread in moister forests throughout the Central Highlands, mainly in State forest, but also on private land. Some 36% of the public native forest is suitable and available for timber harvesting.
The potentially threatening processes associated with timber harvesting may be grouped into three general categories:
the direct impacts of the harvesting operation, including falling, snigging and loading,
the indirect impacts on the site and surrounding vegetation subsequent to harvesting, and
the impacts of a cycle of harvesting (in this case, every 60-120 years) on forest structure, ecology and biodiversity
A key issue in evaluating the ecological impacts of timber harvesting has been the extent to which clearfall harvesting mimics the effect of naturally-occurring wildfire. An attempt will be made to identify similarities or differences between the impacts of clearfelling (including regeneration burning) and wildfire on native flora in the following discussion.
The potentially threatening processes directly associated with the clearfelling operation include damage or loss of individuals, particularly as a result of machinery use and falling trees, disturbance to the superficial soil structure, disturbance of soil-stored seedbanks, compaction of the soil surface on snig tracks and log landings. These potentially threatening processes are strongly associated and of moderate overall significance. The species at greatest risk are those which rely wholly or partially on vegetative reproduction from organs/structures above, at or immediately below the soil surface (eg. Dicksonia antarctica, Cyathea australis, Olearia argophylla, Nothofagus cunninghamii, Persoonia arborea). The direct physical damage to the plants above, at or immediately below the soil surface and disturbance or compaction of the soil itself caused by the use of heavy machinery does not broadly mimic the impact of wildfire. Also potentially at risk are species which rely on soil stored seed for reproduction (eg. Wittsteinia vacciniacea, Persoonia arborea, Bedfordia arborescens, Grevillea barklyana ssp. barklyana, Phebalium wilsonii).
The potentially threatening processes indirectly associated with harvesting operation include habitat modification, specifically the removal of one or more forest strata and the loss of opportunity to develop habitat elements characteristic of mature and senescent forests (eg tall treefern trunks, decaying logs) on the coupe. This threatening process is considered to be strongly associated with timber harvesting and of moderate overall significance. It should be noted that in the Central Highlands no harvesting of old growth occurs in Mountain Ash forest and little in other forest types. In this context, the actual impacts on senescent forest as a result of timber harvesting are limited.
One major impact of this is the alteration of microclimatic conditions both on the coupe and in adjoining vegetation (strongly associated, generally of low overall significance, but highly significant in some vegetation types, eg. Cool Temperate Rainforest). The creation of sharp boundaries between the coupe and adjoining vegetation leads to increased exposure and alteration to the humidity, light and temperature conditions in the adjoining vegetation at least until the regrowth canopy reaches that of the surrounding vegetation. The distance of penetration of these “edge effects”, and their significance in causing floristic changes has yet to be clearly demonstrated, but edge effects are likely to be of greatest threat to species which rely on stable, low light, high humidity, moderate temperature regimes (eg. Hymenophyllum spp, Tmesipteris spp., Polyphlebium venosum, Lastreopsis hispida, Thismia rodwayi). For a review of edge effects and microclimatic changes, see Burgman and Ferguson 1995. The Code of Forest Practices and the Proposed Central Highlands Forest Management Plan provide a range of mechanisms designed to protect rainforest and other gully vegetation from exposure and edge effects.
On the coupe itself, the microclimatic changes following harvesting are radical. While these changes may be similar to the impacts of wildfire in some circumstances, the impact of wildfire may be less extreme in some cases where some vegetation remains after the fire, including burnt or scorched leaves and braches in the canopy or understorey (Keely Ough, pers. comm., Ough and Murphy in prep). Furthermore, it is postulated (Ough and Murphy 1997) that the dense treefern layer (which is present in most ash forests) responds rapidly (ie. within a few weeks) following wildfire to produce a new frond canopy, which has the effect of reducing wind and light, increasing humidity and attenuating temperature extremes at the soil surface and beneath the layer of fronds. These authors have demonstrated a significant increase in treefern mortality following harvesting, when compared to areas burnt by wildfire. Other groundferns and shrubs also resprout more quickly and completely following wildfire than following timber harvesting, hastening the re-establishment of more moderate microclimates (Ough pers. comm).
In addition to the microclimatic amelioration, treeferns may also play a role in the germination and establishment of other forest species, including Pittosporum bicolor, Coprosma quadrifida, Tasmannia lanceolata and Olearia argophylla. Treefern trunks are also the substrate for a suite of epiphytic ferns (eg. Hymenophyllum spp., Tmesipteris spp.) and other epiphytes (eg. Fieldia australis). Other understorey shrubs and trees also provide substrate for epiphytes such as Microsorum pustulatum, as well as a wide variety of non-vascular plants such as mosses and liverworts.
Operational trials of “understorey islands”, areas within coupes in which machinery is excluded to minimise physical damage to long-lived understorey species, are being undertaken in the Central Highlands.
A further indirect potentially threatening process associated with timber harvesting is the facilitation of spread of fungal spores, specifically Chalara australis (the fungal pathogen responsible for Myrtle Wilt disease) via wounds to sensitive species such a Nothofagus cunninghamii (see plant pathogens discussion below, Kile et al 1989). This threat is strongly associated with timber harvesting in some circumstances, although it is known to occur in Cool Temperate Rainforest throughout the Central Highlands, including areas not subject to timber harvesting. Damage occurs naturally through events such as branch fall, but timber harvesting and road construction are also sources of damage. The threat is therefore of moderate significance and discussed in a later section on plant pathogens. The Proposed Central Highlands Forest Management Plan specifies measures aimed at preventing or minimising the spread of the disease and to rehabilitate infected stands where appropriate.
The additional soil disturbance created by timber harvesting (compared to wildfire or other natural disturbances) has the potential to lead to erosion and sedimentation, both on the coupe and in adjoining vegetation, particularly on steeper sites, on granitic soils and in gullies. Some loss of soil-stored seed may also occur. This potentially threatening process is strongly associated with timber harvesting, although its severity may vary greatly from site to site. Its overall significance is considered to be low for plants. Species potentially affected include small forest understorey plants such as Thismia rodwayi and species of mountain stream margins such as Carex alsophila, Wittsteinia vacciniacea, Astelia australiana, Lastreopsis hispida, Huperzia varia, Huperzia australiana and Oxalis magellanica. The Code of Forest Practices specifies provisions to minimise erosion and sedimentation arising from harvesting operations.
The potentially threatening processes associated with a cycle of timber harvesting relate mainly to the frequency and regularity of harvesting (as opposed to that of the natural disturbance regime). A harvesting cycle of 60-120 years applied consistently across the harvested areas of State forest would progressively eliminate mature and oldgrowth growth stages from these areas. The impact of this on native flora would be greatest in situations where the environmental conditions, structure and floristics of forests continue to change with the age of the stand over hundreds of years. Species dependent on habitat elements or characteristics of mature and oldgrowth stands are likely to experience a decline concomitant with the decline in the growth stages themselves (eg. Dicksonia antarctica, Hymenophyllum spp, Tmesipteris spp., Polyphlebium venosum, Thismia rodwayi). Species which require a long period to reach full reproductive maturity may also be at risk (eg. Persoonia arborea). The threatening processes discussed above would be strongly associated with a cycle of clear fall timber harvesting of 60-120 years, were this to be applied, or where a combination of timber harvesting and natural wildfire resulted in a comparable frequency and intensity of disturbance. The overall significance of this is considered to be moderate in the Central Highlands, given that no mature or old growth forest is harvested and timber harvesting is confined to less than 45% of the public mountain ash forest type.
Timber harvesting and associated roading and burning activities are managed under the forest management planning process, which includes the Code of Forest Practices for Timber Production, the relevant Forest Management Plan, regional prescriptions and the annual Wood Utilisation Plans. The Code of Forest Practices for Timber Production and Forest Management Plans are subject to periodic review with formal public consultation, while regional prescriptions and Wood Utilisation Plans are prepared in consultation with regional flora and fauna staff and community input.
The indirect taking of protected flora associated with timber harvesting requires authorisation under the Flora and Fauna Guarantee Act.
Records of timber harvesting have been well maintained since the 1960s. A considerable body of research on the silviculture of forests, particularly ash forests in the Central Highlands, has been undertaken.
More recently, ecological studies carried out by the Department of Natural Resources and Environment have focused on the structural, floristic and ecological impacts of timber harvesting regimes on native forests (Griffiths and Muir 1991, Mueck and Peacock 1992, Ough and Ross 1992, Ough and Murphy 1997, Ough and Murphy in prep).
Detailed, long-term monitoring of harvested areas and comparisons to similar un-harvested areas is not currently being undertaken and the long-term impact of current harvesting systems on the majority of native plants is not well understood.
Planned fire and the planned absence of fire
Fire is a fundamental element of the Australian environment. Most native terrestrial plants have evolved reproductive mechanisms in response to fire. For a general introduction, see Gill et al 1981. Several forms of deliberate fire management are undertaken in the Central Highlands, with a variety of characteristics and impacts.
Ecological burning is generally undertaken to produce an ecologically desirable outcome, including the production of gaps, the reduction in biomass/cover of particular dominant species or to provide a reproductive or growth stimulus to particular target species. Ecological burns vary in intensity, season and frequency depending on the desired outcome. Ecological burns occur very rarely in the Central Highlands, and usually affect very small areas.
The immediate, direct impact of planned fire for ecological purposes is damage or loss of sensitive species. This impact is strongly associated with ecological burning and increases with increasing fire intensity.
Other potentially threatening processes associated (usually weakly associated) with ecological burning tend to become more significant where ecological burning is carried out repeatedly according to a regime which is tailored to narrow outcomes, rather than to maintaining overall diversity. For example, a species may fail to reproduce adequately in a given season. In other situations, the frequency, intensity or season of the fire may be unsuitable, fire may result in the absence of suitable conditions for establishment, or competition from native or introduced species better suited to fire regime may have an impact.
The impacts of ecological burning are of low significance overall, as ecological burning affects only a small proportion of native vegetation and is generally used in vegetation types which are more or less fire tolerant and which have not been burnt for some time. In addition, all ecological burns are the subject of specific plans aimed at the protection of sensitive values on the site.
Fuel reduction burning
This type of burning is undertaken to reduce or remove fuel from the forest floor with the objective of reducing wildfire hazard. Fuel reduction burns are usually of low to moderate intensity, and are undertaken mainly in autumn, when conditions are optimal for maximum effectiveness with low risk of escape or excessive damage to living trees. Frequency varies, with high priority areas (especially near townships and valuable assets) subject to burning every 2 - 5 years, while remaining areas are burnt less frequently, or not at all. Fuel reduction burning is widespread in the drier forests of the Central Highlands, especially in the vicinity of townships, assets such as high tension power lines, pine plantations and in strategic locations in the landscape to protect fire-sensitive vegetation, such as ash forests.
As for ecological burning, the impacts of fuel reduction burning include the direct impact of the fire itself plus the indirect impacts of an imposed fire regime which may differ from the “natural” (pre-European) fire regime.
The direct impact of a fuel reduction burning event is the damage or loss of sensitive species. While this impact is strongly associated with fuel reduction burning, it is of low significance as the vegetation types most frequently burnt are largely comprised of fire resistant or fire tolerant species which are adapted to regenerate by whatever means following fire.
The indirect impacts of an imposed fire regime (mentioned above under ecological burning) while not always strongly associated with fuel reduction burning, may nevertheless be moderately significant overall, and of high significance locally. Detailed burn plans are required to take these issues into account.
Regeneration burning is a standard component of forest management in most harvesting operations in the Central Highlands. It involves the burning of the windrowed or heaped debris from harvesting (including heads, butts, and other material such as unusable logs and non-commercial species). The primary purpose of regeneration burning is to create optimal conditions for the natural germination of eucalypt seed shed from retained seed trees, or for sown seed where this is required. Regeneration burns must be of high intensity to be effective. They usually take place in late summer or early autumn. Unsuitable weather conditions and/or late season harvesting sometimes result in harvested coupes not being burnt until the following season. Regeneration burns occur throughout the Central Highlands where clearfall harvesting systems are employed.
The direct impact of regeneration burning is the damage or loss of fire sensitive species as a result of the fire itself. This impact is strongly associated with regeneration burning, particularly where it may reinforce direct damage or loss during harvesting. At greatest risk are fire sensitive species on the coupe and in the surrounding vegetation. Where the coupe is bounded by gullies, as is often the case in the Central Highlands, regeneration burns can impact upon the gully vegetation (which might include the ecological vegetation classes Cool Temperate Rainforest, Montane Riparian Thicket, Riparian Thicket or Riparian Forest) which tends to comprise a greater proportion of fire sensitive species than other vegetation types. Given also the typically linear configuration of Cool Temperate Rainforest in the Central Highlands, any intrusion of fire has the potential to modify microclimatic conditions (again tending to reinforce changes associated with harvesting itself) to allow the establishment of non-rainforest species. Incremental contraction of rainforest stands may result if the overall pattern of fire favours non-rainforest species, although permanent loss as a result of a single catastrophic wildfire remains the most significant cause of rainforest decline (see Burgman and Ferguson 1995, Cameron 1992, McMahon 1987).
Assuming a harvesting cycle of 60-120 years, the longer-term, indirect impacts of a regime of regeneration burning (failure to reproduce adequately, where the frequency, intensity or season are unsuitable, absence of suitable conditions for establishment as a result of fire regime and competition from native or introduced species better suited to fire regime) are likely to affect only those species which are adapted to fire frequencies greater than 120 years. However, it is important to assess these longer-term impacts of regeneration burning within the broader context of disturbance, which includes harvesting, roading, wildfire and disease in some cases.
The Code of Forest Practices and the Proposed Central Highlands Forest Management Plan contain specific guidelines to prevent damage to surrounding vegetation from regeneration burns, particularly in relation to rainforest and riparian vegetation.
Deliberate exclusion of fire
The deliberate exclusion of fire is a result of successful fire prevention and fire suppression activities directed towards the protection of life, property and other assets. The deliberate exclusion of fire is particularly associated with remnant vegetation on the outer urban fringes in areas where fuel reduction burning may not be regularly undertaken, and where wildfires have been successfully prevented or suppressed.
The threatening processes associated with the long-term absence of fire are the same as those indirect impacts of the types of planned fire discussed above—failure to reproduce adequately, where the frequency, intensity or season are unsuitable, absence of suitable conditions for establishment as a result of fire regime and competition from native or introduced species better suited to fire regime—except that the impacts stem from the lack of fire. Thus the species most likely to be affected are those which are dependent on fire occurring more frequently or more intensely than it does. The vegetation types which are most prone to structural and floristic changes in the absence of fire are lowland heathlands, grasslands and some dry forests.
Predisposing ecological attributes
The preceding discussion considered some of the major impacts of altered fire regimes on native plants. Each species has ecological attributes which may predispose it to threat. The following are examples of species dependent on fire for reproduction, or whose reproduction is greatly enhanced by fire: Lepidium hyssopifolium, Caladenia rosella, Burnettia cuneata, Caladenia concolor, Spiranthes sinensis and Blechnum cartilagineum. Astelia australiana requires very long fire intervals. Some species which are killed by fire are nevertheless dependent on fire to achieve or enhance reproduction, including Banksia spinulosa and Hakea sericea, while others appear to reproduce without the intervention of fire, including Ozothamnus rogersianus and Phebalium wilsonii. Caladenia rosella and Caladenia concolor both require low intensity fire but are killed by high intensity fire
Pultenaea weindorferi, Hymenophyllum cupressiforme, Grevillea repens and Dicksonia antarctica all require long fire intervals, while Astelia australiana and Tmesipteris elongata are restricted to fire sensitive habitats (Cool Temperate Rainforest). Some species are sensitive to fire season, with Burnettia cuneata and Acacia howittii being sensitive to spring fires, while Spiranthes sinensis and Cassinia trinervia are sensitive to summer fires.
The conduct of planned fire in the Central Highlands is governed by the Department of Natural Resources and Environment Code of Fire Practices, Regional Fire Management Plans and Regional Prescriptions in the case of fuel reduction and regeneration burns. Ecological burns are initiated by management plans or Action Statements for specific species, communities or sites.
Records are generally well maintained for ecological burns and regeneration burns. Records for fuel reduction burns generally include the boundary of the burnt area but not the patchiness of the burn. It is therefore difficult to interpret the impact of fuel reduction burning retrospectively.
The Department of Natural Resources and Environment is undertaking long-term research on fuel reduction burns in the Wombat State Forest, which includes vegetation types which are found in the Central Highlands.
In view of the sensitivity of rainforest to fire and the fact that many fire sensitive species occur in rainforest stands, strict controls are placed on burning adjacent to such stands. The Code of Forest Practices provides a buffer of non-rainforest vegetation around each stand to minimise the impacts described above. Less than 15% of all Cool Temperate Rainforest in the Central Highlands occurs in areas that may be subject to planned burning activities.
Grazing or browsing
Domestic stock, feral and naturalised exotic animals, and native browsers are the major agents of grazing or browsing of native vegetation in the Central Highlands.
Grazing of native vegetation by domestic stock is generally undertaken as a supplement to grazing of exotic pasture on private land. In the Central Highlands, it mainly involves grazing by cattle of native vegetation remnants on private land. Very limited stock grazing occurs on public land in the Central Highlands. Historically, one of the major exceptions to this were grazing licences issued over part of the Baw Baw plateau. However, grazing is now excluded from this area. Grazing may also occur along roadsides, especially where droving of stock is being undertaken.
Grazing or browsing by feral and naturalised exotic animals includes the impact of animals which have escaped or been released and have since established significant naturalised populations in the Central Highlands. Included are game animals such as deer, pest animals such as rabbits, pigs and goats, and escaped or abandoned domestic animals such as horses. Grazing or browsing by game and pest animals is widespread in the Central Highlands, with deer mainly occurring in the moister forests of the region. Rabbits are widespread where soil conditions are suitable and the understorey is relatively open. They are not a significant problem in the Central Highlands.
Browsing by native herbivores is only considered as a disturbance in this review where it is significantly beyond the natural range of impact (over-browsing). This is usually restricted to cases where populations of native browsers become concentrated beyond carrying capacity in confined or isolated areas of native vegetation. Over-browsing by native herbivores is virtually unknown in the major blocks of public land, but may be a significant problem in some public land blocks and on private land in the northern parts of the region.
The major threatening process strongly associated with grazing or browsing is the direct damage or loss of plants as a result of browsing and/or trampling, and the potential for reduced reproductive output, especially where reproductive structures are significantly affected by grazing. The less direct potentially threatening processes associated with grazing are habitat modification in the form of soil disturbance or erosion, particularly where grazing or trampling is intense, or where site conditions exacerbate the impact, for example, on steep sites, in drainage lines or on particular soil types (heavy clays - pugging; sands, silts and gravels - erosion; peats - physical fragmentation). Another less direct potentially threatening process associated with grazing is environmental weed invasion (see below), where soil disturbance is combined with animals acting as seed dispersal vectors, via seed in manure or adhering to hooves or coats.
The ecological attributes which predispose plants to threat from grazing include palatability (mainly herbaceous species, but may include woody species when
young, such as Orchidaceae, some Eucalyptus spp,some Acacia spp, Coprosma spp) and occurrence in habitats which tend to be grazed more frequently or heavily, such as grassy habitats (examples include Lepidium hyssopifolium, Senecio macrocarpus, Cullen tenax, Amphibromus pithogastris, Senecio laticostatus).
The current overall significance of the threatening processes associated with grazing or browsing in the Central Highlands forests is considered to be low, but significantly higher in the habitats which are most affected, principally the predominantly grassy and forb-rich ecological vegetation classes such as Plains Grassland, Plains Grassy Woodland, Box Woodland, Floodplain Riparian Woodland, Grassy Dry Forest and Valley Grassy Forest, and associated wetlands. The historical combination of alienation, grazing and clearing has resulted in these ecological vegetation classes being scarce on public land (with the exception of Grassy Dry Forest) and are often present as more or less degraded remnants on private land.
Grazing of private land remnant native vegetation is a management practice carried out by many landholders. It is not subject to regulation. Licensed grazing of native vegetation on public land is subject to periodic review, with the option of specifying licence conditions. As indicated above very little public land in the Central Highlands is licensed for domestic stock grazing.
Pest animals such as rabbits are subject to active management to control or eradicate populations, especially adjacent to agricultural lands and where impacts are most severe. Targeted pest management is applied in a few cases where grazing is a threat to one or more threatened species as a component of an Action Statement or Recovery Plan. The recent release of the Rabbit Calicivirus Disease is a major initiative in rabbit control. Its effectiveness will come to light once the results of monitoring programs are published.
Game animals such as deer are neither actively controlled nor encouraged. Their impact is relatively minor when compared to domestic stock and rabbits.
Overbrowsing by native browsers is generally dealt with by issuing permits to reduce the relevant populations.
The impacts of grazing are poorly understood, with most inferences being drawn from anecdotal or incidental observation. Further investigation of the impacts of grazing, particularly regarding the resilience of the native vegetation, its role in environmental weed spread and fuel management is warranted.
Road construction and maintenance
Road construction and maintenance may involve the clearing of vegetation, major earthworks to form the road pavement and batters, and works to construct bridges, culverts and drains. A variety of classes of roads and tracks are constructed on public land, both in conservation reserves and State forest to provide access for commercial timber harvesting, fire management, catchment management and recreation.
The impact of road construction and maintenance is greatest in the construction phase, especially where the road is major and the terrain is steep, requiring large batters. Stream crossings sometimes present major engineering challenges, and have been shown to be the main sources of sediment input to streams. The erosion hazard will also be greatest in steep terrain, particularly in high rainfall areas. Gully vegetation is therefore most at risk from the major impacts of road construction and maintenance.
Road construction and maintenance is widespread throughout the Central Highlands, but particularly in timber harvesting areas, where there is a requirement for a well constructed and maintained network of roads capable of carrying heavy vehicles. However, in terms of overall length, narrow tracks, which are generally constructed and maintained by bulldozers, constitute the majority or the road and track network in the Central Highlands.
The potentially threatening processes associated with road construction and maintenance include direct damage or loss of plants by machinery (strongly associated, but generally of low overall significance), habitat loss and/or fragmentation (strongly associated, but generally of low overall significance), habitat modification - erosion and sedimentation (strongly associated, but generally of moderate overall significance), habitat modification - altered micro-climatic and light conditions (strongly associated, but generally of moderate overall significance), introduction of soil or gravel contaminated with weed seed or fungal spores (strongly associated and of high overall significance) and facilitation of weed spread due to continual disturbance of road margins (strongly associated but of moderate overall significance).
The potentially threatening processes based on habitat modification (soil erosion, sedimentation, microclimatic changes) are most significant in the vicinity of gullies in the steeper, higher-rainfall, mountainous parts of the Central Highlands. Thus, species of wet gullies are likely to be most susceptible to these threats, including Astelia australiana, Lastreopsis hispida, Huperzia varia, Hymenophyllum cupressiforme and Phebalium wilsonii. Species which are sensitive to increased exposure may also be threatened, including Euchiton umbricolus, Blechnum wattsii, Tmesipteris elongata var elongata and Gahnia grandis. The impact of road construction and maintenance, particularly its role in the spread of weeds and disease, and its association with a range of edge effects, has not been thoroughly investigated.
Species sensitive to weed invasion include Grevillea barklyana ssp. barklyana, Oxalis magellanica, Pterostylis grandiflora and Pultenaea weindorferi, whilst those sensitive to plant disease include Grevillea repens, Banksia spinulosa var. cunninghamii, Hakea sericea and Persoonia arborea. Vicroads (a Victorian Government agency) is responsible for the highways throughout Victoria. Vicroads has recently published an environmental strategy which includes objectives and commitments relating to the conservation of native flora.
Local municipalities are responsible for road construction and maintenance for other roads, excluding those managed by Department of Natural Resources and Environment and some other organisations such as utilities on public land, and those managed by private landholders on their land.
Road construction and maintenance conducted on public land as part of the management of State forests or major conservation reserves is planned and implemented as part of a coordinated management plan. The Code Of Forest Practices For Timber Production includes standards and guidelines for road construction in State forests, particularly in relation to gully and riparian vegetation. In all cases, efforts are made to reduce the environmental impacts consistent with safety considerations, traffic levels and engineering requirements. Such factors will affect the extent to which desired environmental outcomes can be accommodated. Road construction and maintenance is generally well planned, and as a result, records are well maintained.
A wide range of recreational pursuits take place in the Central Highlands, but the most significant are vehicle based activities such as fishing, hunting, camping and tourism, and skiing.
The impacts of vehicle based activities include the localised disturbance of habitats in the vicinity of focal points such as camping areas and features, such as waterfalls, views, and historic places, and localised erosion and sedimentation, particularly of streams and stream banks at crossing points, especially in areas where there are high levels of vehicle use, especially four wheel drive vehicles. Vehicle use can also result in the transport of soil, potentially carrying plant diseases and weed propagules.
Vehicle-based activities are widespread throughout the Central Highlands. The impacts are greatest in localised areas of the major river valleys, such the Yea, Acheron, Murrindindi, Royston, Big, Goulburn, Thomson, Aberfeldy, Tyers, Tanjil, Bunyip and Yarra, especially when they occur in the riparian zone.
Snow sports (including down hill and cross country skiing and snow play) and associated development of facilities is a significant, albeit highly localised, form of recreation in the Central Highlands. Its impacts include clearing, habitat fragmentation and habitat disturbance during in the construction and maintenance of facilities (runs, trails, lifts, buildings, utilities infrastructure), pollution (particularly from sewerage systems) and associated indirect impacts such as the spread of environmental weeds.
Snow sport and associated resort development are confined to the Baw Baw plateau (Baw Baw Village: downhill and cross-country skiing, Mt St Gwinear: cross-country skiing), Lake Mountain (cross-country skiing) and Mt Donna Buang (sightseeing, tobogganing).
The potentially threatening processes associated with recreation activities are habitat loss (strongly associated but highly localised and of low overall significance), habitat degradation (strongly associated, localised and of low overall significance), introduction of environmental weeds (strongly associated and of high significance), introduction of plant pathogens (strongly associated and of moderate overall significance) and pollution/eutrophication of subalpine wetlands and streams (weakly associated and of low overall significance).
The species likely to be at greatest risk from recreational activities include species of riparian zones (eg. Eucalyptus crenulata, Burnettia cunetata, Gahnia grandis, Epilobium pallidiflorum, Huperzia varia, Astelia australiana), species which are sensitive to weed invasion (eg. Eucalyptus crenulata, Epilobium pallidiflorum, Eucalyptus neglecta, Astelia australiana), species which are sensitive to plant pathogens (eg. Grevillea repens, Banksia spinulosa var. cunninghamii, Hakea sericea, Persoonia arborea) and species of wet subalpine heathlands (eg. Coprosma moorei, Juncus antarcticus, Epacris glacialis, Mitrasacme montana, Lycopodium scariosum). Vehicle-based activities such as pleasure driving, fishing, hunting, camping and sightseeing are managed through the relevant planning process—Forest Management Area Plan or National Park Management Plan—on public land. Effort is generally made to encourage activities in appropriate zones in which they are compatible with overall management objectives, or where impacts can be minimised.
Snow sport and associated resort development at Mount Baw and Lake Mountain Alpine Resorts are managed by the Alpine Resorts Commission (ARC). The Commission is required to take into account a range of legislation including provisions of flora and fauna guarantee and local planning requirements. The LCC recommendations (Land Conservation Council 1994) specify that ski trail works be undertaken in accordance with guidelines agreed by ARC and NRE, and that a development and management plan be agreed by ARC and NRE for further new major works at Lake Mountain. For major developments an EIS can be required which would consider flora and fauna values of the area. Environmental management plans are currently being developed by the ARC for alpine resorts.
Environmental weed invasion
Environmental weed invasion is not a direct, human-induced disturbance in most cases - it is a phenomenon which would in all likelihood now continue without any of the direct disturbances that it normally accompanies. It involves the naturalisation and spread of exotic taxa and the extension beyond “normal” range or habitat of native species.
The impact of environmental weeds varies. Some are relatively benign, occurring at low cover/abundance levels and/or spreading slowly. Others spread rapidly due to high reproductive output, large dispersal ranges and/or broad habitat tolerances. The most destructive environmental weeds are those which out-compete native species to the extent that the habitat can become grossly modified, with particular niches being lost altogether.
Environmental weeds are widespread throughout the Central Highlands, occurring in all habitats and areas. Among the most destructive or aggressive exotic weeds are Blackberry (Rubus fruticosus spp. agg.), St Johns Wort (Hypericum perforatum), Blue Periwinkle (Vinca major), Quaking Grasses (Briza spp.), Japanese Honeysuckle (Lonicera japonica), Himalayan Honeysuckle (Leycesteria formosa), Holly (Ilex aquifolium), English Ivy (Hedera helix), English Broom (Cytisus scoparius), Cotoneaster (Cotoneaster spp.), Yorkshire Fog (Holcus lanatus) and Canary Grasses (Phalaris spp.). The native species of greatest concern are Sweet Pittosporum (Pittosporum undulatum) and Cootamundra Wattle (Acacia baileyana).
The potentially threatening processes associated with environmental weed invasion are competition and habitat modification (both strongly associated and of high significance). Species likely to be at greatest risk from environmental weed invasion are those which occupy weed prone habitats, such as riparian zones, relatively fertile soil types and fragmented habitats in close proximity to weed sources, such as waste disposal areas and agricultural lands. Examples of species likely to be most affected include Caladenia rosella, Desmodium varians, Epilobium pallidiflorum, Eucalyptus crenulata, Eucalyptus neglecta, Eucalyptus strzeleckii, Eucalyptus yarraensis, Euchiton umbricolus, Grevillea barklyana ssp. barklyana, Lepidium hyssopifolium, Lindsaea microphylla, Oxalis magellanica, Pterostylis grandiflora, Pultenaea weindorferi, Senecio laticostatus, Senecio macrocarpus, Taraxacum aristum and Wittsteinia vacciniacea. The management of environmental weed invasions is the responsibility of the land manager. On public land, environmental weeds are considered along with agricultural weeds under the Victorian Catchment and Land Protection Act 1992. Under this Act, weed species may be listed as State Prohibited, Regionally Prohibited or Regionally Controlled weeds. Within this framework, regional environmental weed management priorities are established through the relevant management plans.
The Victorian Parliament, through the Environment and Natural Resources Committee, is currently investigating the significance of the weed problem in general, including specific reference to environmental weeds. Environmental weed invasion has been listed as a potentially threatening process under the Flora and Fauna Guarantee Act.
The Commonwealth, in consultation with State and Territory agencies, has recently completed the National Weeds Strategy, which outlines strategies to address major issues. Current management of environmental weeds across public and private land is generally acknowledged as being deficient. Limited resources and a general lack of strategic planning, tactical planning, follow-up, monitoring and experimental management are largely responsible for the deficiencies.
The distribution of environmental weeds is generally well understood, as a result of their inclusion in floristic surveys conducted in the Central Highlands. A considerable amount of research on the ecology and management of particular environmental weeds, especially those which impact on agriculture, has been undertaken.
The most significant gaps in knowledge are:
the ecology of a suite of environmental weeds which do not impact significantly on agriculture,
the long-term management of multi-species invasions,
the relationship between weed invasion and other disturbances.
Like environmental weed invasion, the introduction, spread and disease caused by plant pathogens is not a direct, human-induced disturbance, although it can be exacerbated by other disturbances. The most important plant pathogens in the Central Highlands are the introduced Cinnamon Fungus (Phytophthora cinnamomi), which is responsible for dieback disease, and the apparently endemic fungus Chalara australis which causes Myrtle Wilt, a disease of the rainforest tree Myrtle Beech (Nothofagus cunninghamii).
Dieback disease caused by Cinnamon Fungus (Phytophthora cinnamomi)
Cinnamon Fungus is widespread in the Central Highlands. However, dieback disease and its consequent impact on vegetation tends to be more localised. Cinnamon Fungus was previously thought only to lead to significant disease occurrence in susceptible species under particular soil conditions (warm and moist), and was therefore a threat only in particular areas, such as low elevation heathlands with impeded drainage. However, recent research from Tasmania (Podger and Brown 1989, Podger et al 1989) suggests that the disease may pose a threat in mountain areas where soils tend to be moist, well-drained but generally substantially cooler than those at lower elevations.
Dieback disease caused by Cinnamon Fungus leads to the morbidity or mortality of some or all infected individuals of susceptible species, including members of the Proteaceae family such as Banksia spinulosa var cunninghamii, Hakea sericea, Grevillea repens and Persoonia arborea. It has been reported that Cinnamon Fungusmay affect Astelia australiana, but the most recent investigation (Turner et al 1996) suggests that “although a variety of potentially pathogenic fungi, including Phytophthora cinnamomi, were located throughout the Central Highlands habitat of A. australiana, their distribution did not correlate with an increased incidence of dead and sick plants”.
The proportion of a population of a species that is susceptible to dieback disease and the reproductive output of the species will largely determine whether the onset of the disease acts as a transient selection pressure or a catastrophic epidemic which decimates and possibly eliminates the population. Where structurally-dominant species are affected (such as eucalypts), dieback disease can modify the habitat to the extent that some species may be threatened, although this has not been widely reported from the Central Highlands. The overall significance of the threat posed by dieback disease in the Central Highlands forest is considered to be low and moderate for other vegetation types such as heaths and heathy woodland.
Dieback disease caused by Cinnamon Fungus (Phytophthora cinnamomi) is managed by a combination of measures including quarantine of disease-affected areas, hygiene procedures designed to remove infected soil from vehicles and kill spores, research and monitoring of infected sites and affected species.
The West Australian Department of Conservation and Land Management, in consultation with relevant Commonwealth, State and Territory agencies, is currently preparing a National Threat Abatement Plan for Phytophthora.
Myrtle Wilt disease is widespread in the Central Highlands, with most catchments supporting Myrtle Beech -dominated Cool Temperate Rainforest exhibiting low levels of disease symptoms, a few hotspots, and a few apparently disease-free areas (Cameron and Turner 1996). Myrtle Wilt disease leads to mortality in all cases. Infection occurs via wounds and root grafts between individuals. In many cases, the disease appears to occur naturally at low levels of infection and in equilibrium. However, disturbance of rainforest stands has been shown to elevate the incidence of the disease (Kile et al 1989, Neyland and Brown 1994). The most significant threat associated with elevated incidence of Myrtle Wilt is habitat modification in the form of the creation of gaps in the rainforest canopy. The gaps may become so large as to fragment the mainly linear stands found in the Central Highlands. In combination with fire and permanent roading, this may lead to a significant contraction and fragmentation of rainforest stands. The species at greatest risk from this process are those dependent on rainforest habitats, and include Astelia australiana, Huperzia varia, Huperzia australiana, Tmesipteris elongata ssp. elongata, Tmesipteris ovata, Hymenophyllum cupressiforme and Lastreopsis hispida The Code of Forest Practices for Timber Production specifies additional buffering of rainforest stands where Myrtle Beech comprise more than 20% of the canopy is required and any road construction adjacent to rainforest areas is to be avoided wherever possible. Specific management prescriptions for rainforest and guidelines for Myrtle Wilt management are outlined in the Proposed Central Highlands Forest Management Plan.
Current management of Myrtle Wilt on public land focuses on monitoring disease incidence and the nature of the regeneration in gaps created by the disease. Further research is recommended to determine the relationship between disturbance and disease and the critical environmental factors which limit or facilitate its spread.
The following disturbances are considered to be relatively minor in their impact on native flora in the Central Highlands.
Input of pollutants to native vegetation may come from a variety of sources, including herbicides used in pest control, agricultural fertilisers, sewage, spillage of industrial chemicals and use of fire retardant chemicals. Of these, excessive nutrient input probably has the most significant impact, especially where it is associated with vegetation types which are adapted to low nutrient soils. It may facilitate the spread of environmental weeds in some circumstances.
Genetic pollution of natural populations of native flora is most likely to occur as a result of the establishment of plantations of silvicultural or horticultural species closely related to native species within reproductive range. The advent of genetically-modified types may increase the impact. The other major source of genetic pollution is as a result of the use of non-local provenance seed or seedlings in re-afforestation or forest regeneration following harvesting. This is not currently practised, although tended to occur more frequently in the past. Although potentially significant, major impacts have not been revealed by research to date.
Deliberate collection is a significant disturbance or threat to a small number of taxa which are considered to be desirable by collectors. Most collectors are believed to be amateurs acting alone rather than commercially-motivated (cf. deliberate collection of fauna). Most at risk are the native orchids, particularly terrestrial orchids including Caladenia spp., Diuris spp., Calochilus spp. and Prasophyllum spp., and epiphytic orchids such as Sarcochilus australis.
5.3.4 Relationship between human-induced and natural disturbances
The distinction between natural disturbances and the processes of evolutionary change is blurred. For the purposes of this review, natural disturbances are those events which are random or cyclic but which occur relatively frequently (in the tens or hundreds of years) as opposed to changes which are irreversible and tend to form longer-term trends over thousands of years.
A range of natural disturbances affect native flora in the Central Highlands, the most notable being:
landslides and other geomorphological changes
Each of these natural disturbances, either alone or combined, has the potential to cause significant changes in the floristic composition and structure of native vegetation, including the decline or extinction of species at a local or regional level.
Generally speaking, little or no effort is expended to protect native flora from the impacts of natural disturbances. Where the impacts of such disturbances are mitigated, it is usually incidental to efforts to protect human life, property and commercial assets.
However, the interactions between natural and human-induced disturbances are likely to be significant in many cases, and warrant further investigation and consideration when attempting to ameliorate the impacts of human-induced disturbances.