Long-Term Empirical Studies Highlight Multiple Drivers of Temporal Change in Bird Fauna in the Wet Forests of Victoria, South-Eastern Australia

Old growth is a critical growth stage in many forest types globally. It has many key ecological roles including biodiversity conservation, carbon storage and the provision of services such as water production. The extent of old growth forest has been declining in many ecosystems around the world, with major ecological and ecosystem service consequences. Important insights about such declines, as well as the structure, function and conservation of old growth forest, can be gained from detailed cross-sectional and longitudinal studies of different age cohorts within a given forest ecosystem. In this review article, we outline key insights into the characteristics of, and threats to old growth forests, using the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria, south-eastern Australia as a detailed case study. These forests are dominated by the tallest flowering plants on earth and have been subject to several decades of intense study. These studies show that old growth Mountain Ash forests are characterized by (among other features): giant trees (approaching 100 m tall and sometimes exceeding 20 m in circumference), numerous trees with hollows, an understorey ofAcaciaand rainforest trees, a range of plant and animal species that are rare or absent in younger aged stands, and moist, nutrient-rich soils. The area of old growth Mountain Ash forest has declined to 1.16% of the ∼141,000 ha area occupied by ash-type forests in the Central Highlands region. This is up to 60 times less than it was at the time of European colonization ∼220 years ago. The loss of old growth has major implications for bird, mammal and other biodiversity, as well as for carbon storage and water production for human consumption. The main drivers of old growth decline are recurrent wildfire, widespread clearcutting, and a logging-fire interaction in which cut and then regenerated forests become more flammable and are at significantly elevated risk of burning at high (stand replacing) severity. Climate change is also a driver of old growth decline both through elevating the mortality of large old living trees and underpinning an increase in the frequency of high severity wildfire. These interacting drivers mean that restoring old growth Mountain Ash forest will be an ecological and policy challenge. We argue that a first step must be to cease all commercial logging in the Mountain Ash ecosystem to allow new cohorts of old growth forest to be recruited and thereby expand the extent of the old growth estate. In addition, the Government of Victoria should revert to a past definition of old growth that made it easier for forest to qualify for protection. Given there are high risks of recurrent high-severity wildfire in the existing Mountain Ash forest estate which is dominated by highly flammable young regrowth forest, new technologies (such as the use of drones and satellites) are needed to rapidly detect and then suppress ignitions before fires become large and difficult to control. Mountain Ash forests have provided an important natural laboratory for understanding the dynamics, management and conservation of old growth forest. They have also helped generate some valuable general perspectives likely to be relevant to other forest ecosystems globally. These include: (1) the critical value of multi-facetted cross-sectional and longitudinal studies in quantifying attributes of, and threats to, old growth forest, (2) the need for a carefully crafted definition of old growth that will typically be ecosystem-specific and based on the time required to develop key ecosystem attributes (e.g., large old trees), (3) the importance of rigorous protection measures because poor decisions that result in the loss of old growth now will take prolonged periods to rectify, and (4) setting protection levels that are relative to the existing spatial coverage of remaining old growth and the extent and impacts of stressors driving old growth decline.

Old forest, new perspectives—Insights from the Mountain Ash forests of the Central Highlands of Victoria, south-eastern Australia

Temporal patterns of vegetation recovery after wildfire in two obligate seeder ash forests

Increases in forest disturbances have altered global forest demography rates, with many regions now characterized by extensive areas of early-successional forest. Heterogeneity in the structure, diversity, and composition of early-successional forests influence their inherent ecological values from immediately following disturbance to later successional stages, including values for biodiversity and carbon storage. Here, using 14 years of longitudinal data, we describe patterns in the structure, richness, and composition of early-successional forests subject to one of three different disturbance types: (1) clearcut logging followed by slash burn, (2) severe wildfire followed by salvage logging, and (3) severe wildfire only, in the Mountain Ash (Eucalyptus regnans) and Alpine Ash (Eucalyptus delegatensis) forests of southeastern Australia. We also documented the influence of disturbance intervals (short, medium, and long) on early-successional forests. Our analyses revealed several key differences between forests that regenerated from wildfire versus two different anthropogenic perturbations. Most ash-type plant communities were resilient to wildfire within historical fire-regimes (75-150 years), exhibiting temporal trends of recovery in plant structure, richness, and composition within the first decade. In contrast, the richness, occurrence, and abundance of some plant lifeforms and life history traits were negatively associated with clearcut logging and salvage logging, relative to forests disturbed by wildfire alone. These included resprouting species, such as tree ferns and ground ferns. However, Acacia spp. and shrubs were more abundant after clearcut logging. Our findings also provide evidence of the pronounced negative impact of salvage logging on early-successional plant communities, relative to that of both clearcut logging and wildfire. Notably, plant richness declined for over a decade after salvage logging, rather than increased as occurred following other disturbance types. Early-successional forests provide the template for the stand structure and composition of mature forests. Therefore, altered patterns of recovery with different disturbance types will likely shape the structure and function of later-successional stages. Predicted increases in wildfire will increase the generation of early-successional forests and subsequent salvage logging. Therefore, it is pertinent that management consider how different disturbance types can produce alternate states of forest composition and structure early in succession, and the implications for mature stands.

Forest disturbance, forest wildlife conservation and the conservative basis for forest management in the mountain ash forests of Victoria—Comment

It is often stated that the availability of N limits the rate of growth of native forests. We discuss this hypothesis with particular reference to the mountain ash ( Eucalyptus regnans ) forests of south-eastern Australia. The abundance of 15 N in leaves and soil of mountain ash forest is in accord with data for Northern Hemisphere temperate forests and for tropical forests,and indicates that N availability is relatively high.None of the nutrient elements has limited the rate of growth of mountain ash forest regenerating after major disturbance (clear-felling and intense wild-fire). There is some evidence that P may be limiting to some ecological processes (e.g. the rate of litter decomposition). We conclude that phosphorus is more likely to be limiting than nitrogen in mountain ash forest because nitrogen cycling is conservative and continual inputs of N through biological fixation supplement this conservative N supply, and the stands never become N-deficient. The development of methodologies to determine the rate of N2-fixation in forests should be of high priority in ecological research.

Carbon and nitrogen in forest soils: Potential indicators for sustainable management of eucalypt forests in south-eastern Australia

Variable retention harvesting is a silvicultural system that focuses on retaining key elements of stand structure at the time of logging and is increasingly being used worldwide. We describe the design and establishment of a variable retention harvesting experiment established in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria, south-eastern Australia. The experiment was instigated in 2003, and the work to date has shown that it has environmental benefits for certain groups of small mammals, birds, and vascular plants. The experiment has been integrated with an ongoing long-term monitoring program as well as other experiments such as those in post-fire salvage-logged areas. Collectively, the results of various studies suggest that the potential value of variable retention harvesting extends beyond green-tree logging to post-fire salvage logging environments.We outline some of the challenges in, and new perspectives derived from, implementing and maintaining our experiment. This included difficulties protecting islands from high-intensity post-harvest regeneration burns and threat of declining funding undermining ongoing project viability. A critically important perspective concerns the ecological and economic context in which variable retention harvesting is implemented. In the particular case of Mountain Ash forests, assessments using formal IUCN criteria classify the ecosystem as being Critically Endangered under the Red Listed Ecosystem approach. As a result, Mountain Ash forests are at a high risk of ecosystem collapse. Further logging will increase that risk, making the basis for continued harvesting questionable. In addition, economic analyses suggest that the value of natural assets, like water production, far outweigh the value of the wood products harvested from the Mountain Ash ecosystem, again leading to questions about the viability of ongoing harvesting. We therefore conclude that whilst variable retention harvesting has the potential to contribute to biodiversity conservation in Mountain Ash forests, broader ecological and economic contextual issues (such as the values of competing resources like water yields and the heavily degraded state of the forest) may erode the case for its broader application.

Forests globally are subject to disturbances such as logging and fire that create complex temporal variation in spatial patterns of forest cover and stand age. However, investigations that quantify temporal changes in biodiversity in response to multiple forms of disturbance in space and time are relatively uncommon. Over a 10-yr period, we investigated the response of bird species to spatiotemporal changes in forest cover associated with logging and wildfire in the mountain ash (Eucalyptus regnans) forests of southeastern Australia. Specifically, we examined how bird occurrence changed with shifts in the proportion of area burned or logged in a 4.5km radius surrounding our 88 long-term field survey sites, each measuring 1ha in size. Overall species richness was greatest in older forest patches, but declined as the amount of fire around each site increased. At the individual species level, 31 of the 37 bird species we modeled exhibited a negative response to the amount of fire in the surrounding landscape, while one species responded positively to fire. Only nine species exhibited signs of recovery in the 6 yr of surveys following the fire. Five species were more likely to be detected as the proportion of logged forest surrounding a site increased, suggesting a possible "concentration effect" with displaced birds moving into unlogged areas following harvesting of adjacent areas. We also identified relationships between the coefficients of life history attributes and spatiotemporal changes in forest cover and stand age. Large-bodied birds and migratory species were associated with landscapes subject to large amounts of fire in 2009. There were associations between old growth stands and small-bodied bird species and species that were not insectivores. Our study shows that birds in mountain ash forests are strongly associated with old growth stands and exhibit complex, time-dependent, and species-specific responses to landscape disturbance. Despite logging and fire both being high-severity perturbations, no bird species exhibited similar responses to fire and logging in the landscape surrounding our sites. Thus, species responses to one kind of landscape-scale disturbance are not readily predictable based on an understanding of the responses to another kind of (albeit superficially similar) disturbance.

The catastrophic 2009 wildfires in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria provided an opportunity to gain new insights into the responses to fire by various elements of the biota. Ongoing long-term monitoring at a large number of permanent field sites for up to 25 years prior to the fire, together with 10 years of post-fire monitoring, has provided an unparalleled series of datasets on mammal, bird, and plant responses on burned and unburned sites. The empirical studies briefly summarized in this paper show patterns of steep declines in large old trees and declines in site occupancy by arboreal marsupials and birds. These changes contrast markedly with the responses of the two most common species of small mammals (the Agile Antechinus [Antechinus agilis] and Bush Rat [Rattus fuscipes]), which recovered within two generations after the fire. Declines in arboreal marsupials, birds and large old trees have also occurred on unburned sites, indicating an ecosystem-wide trend. In general, logging had a greater impact than fire on the majority of groups of birds and plants, particularly post-fire salvage logging that occurred in some areas following the 2009 wildfires. Beyond interactions between fire and post-fire (salvage) logging and their effects on forest biota, we have uncovered evidence of other kinds of interactions in Mountain Ash forests. These include interactions between: (1) the severity of fires and logging history, (2) post-fire bird population recovery and long-term climate and short-term weather conditions, and (3) impacts on forest soils. The structure and landscape composition of the Mountain Ash ecosystem has been radically altered over the last century. This has resulted from the combined impact of several large fires, including the 2009 fires as well as widespread clearfell logging that has been conducted within state forests over the last 50 years. The ecosystem now supports old growth cover that is 1/30th to 1/60th of what it was estimated to have been prior to European settlement. The ongoing decline of key components of the Mountain Ash ecosystem has led to it being classified as Critically Endangered and at high risk of ecosystem collapse. We argue that current forest policy and practices need to better mitigate the effects of fire on this already highly disturbed forest and enhance the possible persistence of species in this ecosystem. Several key strategies are required to do this. First, there is a need to significantly expand the extent of old growth within the Mountain Ash forest estate. This is because fire severity is diminished in such areas. Spatial contagion across old-growth dominated landscapes also may be suppressed relative to landscapes composed primarily of young forest. Allied management strategies include the protection of more mesic parts of Mountain Ash landscapes as these are less likely to burn or at least burn at high severity. Such enhanced protection should include an expanded network of buffers around drainage lines and waterways as these are where fire severity is likely to be lowest and also where old growth elements like large old hollow-bearing trees are more abundant. In addition, all existing living and dead hollow-bearing trees need to be protected by buffers of unlogged forest within wood production forests to promote their standing life and better conserve cavity-dependent fauna such as the Critically Endangered Leadbeater’s Possum (Gymnobelideus leadbeateri) and other declining taxa like the Greater Glider (Petauroides volans).

Forest ecosystems contain several climate‐sensitive drivers that respond differentially to changes in climate and climate variability. For example, growth and regeneration processes are “stand‐scale” drivers, while natural disturbances operate at “landscape scale”. The relative contributions of these different scale drivers of change in ecosystems create great uncertainty when simulating potential responses of a forest to changes in climate.Here, we assess those contributions, along with harvesting effects, on biomass (both total and of individual species) in the southern boreal forest of Canada under three climate scenarios (RCP2.6,RCP4.5 andRCP8.5).Projections were performed for three future 30‐year time periods, in four study regions located on an east–west transect, using a forest landscape model (LANDIS‐II), parameterized using a forest patch model (PICUS). Projected future impacts were assessed for each driver of change, and found to vary greatly among regions, species, future period and forcing scenarios. Fire, and stand‐scale climate‐induced impacts, had the strongest effects on forest vegetation, as well as on total and species’ biomass under mostRCPscenarios, but the largest impacts occurred mostly after 2050, particularly with theRCP8.5 scenario.The relative importance and trends in species‐specific impacts varied, both spatially and according to the differentRCPscenarios. Western regions were generally more sensitive to stand‐scale climate‐induced changes, whereas eastern regions were more sensitive to changes in fire regime. Our study also highlights the importance of considering the prevalence of species‐level functional traits when assessing the sensitivity of forest landscapes to a given driver of change in the context of increasing anthropogenic climate forcing.Synthesis. Increases in fire activity, and direct impacts of climate change on forest growth and regeneration, will be the most important drivers of future changes in southern boreal forest landscapes.

Effective conservation of forest biodiversity and effective forest restoration are two of the biggest challenges facing forest managers globally. I present four general principles to guide strategies aimed at meeting these challenges: (1) protect and restore populations of key species and their habitats, (2) conserve and restore key attributes of stand structural complexity, (3) maintain and restore natural patterns of landscape heterogeneity, and (4) maintain and restore key ecological processes. The complexity associated with these principles is that how they will be practically implemented on the ground will invariably be ecosystem specific as what constitutes stand structural complexity or landscape heterogeneity will vary between ecosystems. Here I demonstrate the practical application of the four general principles in a detailed case study of conservation and restoration in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria, south-eastern Australia. These forests are characterized by declining species, loss of key elements of stand structural, loss of old growth forest, altered patterns of landscape heterogeneity, and altered ecosystem processes. I highlight how altered management practices in Mountain Ash forests that are guided by our four general principles can help conserve existing biodiversity and underpin effective forest restoration. Consideration of our general principles also can identify policy deficiencies that need to be addressed to enhance restoration and biodiversity conservation.

Patterns of avian species richness and assemblage composition may change markedly between and within vegetation types. We compared bird species richness and assemblage composition in cool temperate rainforest and Mountain Ash (Eucalyptus regnans) forest in the Central Highlands of Victoria, south-eastern Australia. We quantified the effects of the age of stands of Mountain Ash on the extent of forest-type differences with cool temperate rainforest. We also explored the influence of the shape of stands of cool temperate rainforest on bird species richness and the composition of the bird assemblage. We found no significant differences in bird species richness between cool temperate rainforests and Mountain Ash forest. This result was consistent with subtle differences in the composition of the bird assemblage, with few bird taxa being totally excluded from either of the two forest types. Some species (e.g. Pink Robin (Petroica rodinogaster)) were significantly more likely to be recorded in cool temperate rainforest but were not uncommon in Mountain Ash forest. We found no evidence of significant effects of stand shape in cool temperate rainforest, which was consistent with analyses of bird assemblages given that most species occurred in both forest types. Hence, we uncovered no evidence of specialist taxa confined to cool temperate rainforest.

Single large versus several small: The SLOSS debate in the context of bird responses to a variable retention logging experiment

Mountain ash (Sorbus aucuparia) is widespread in nearly whole Europe from sea level to timberline. On north exposed peaks of some mountains of the Southern Alps (Ticino/ Switzerland and North Italy/ Verbano-Ossola) small mountain ash forests build the forest limit above 1500 m, so at Monte Lema, Monte Morissolo, I Balmit and Mottarone. Mountain ash often occurs on former forest clearings as pioneer tree as secondary plant succession. On some sites, mountain ash will be replaced later by beech as climax species. At all sites, we recognized a weak or missing generative mountain ash reproduction. One reason for that could be the dense grass cover of small-reed, Calamagrostis spec. which inhibits the establishment of rowan seedlings; other reasons could be insect and game damage, mycosis and other diseases. Vegetative propagation like root bulbils, suckers and shoots from stump are important survival strategies of mountain ash. So, at some sites have been recorded a high share of polyphyletic single young trees. At all sites, count of annual rings of 25-50 mountain ash trees revealed an average age of 40-55 years. Green alder and mountain ash often occur together within the Alnetum viridis as well as in the mountain ash forest. In the green alder bush, mountain ash occurs only as single trees, whereas Alnus viridis can dominate in both plant communities. At the southernmost sites, there is a marked weak abundance of green alder due to dryer climate. Within mountain ash forests of the Southern Alps, the typical tall perennial herbs of the green alder bush are more or less absent because of low rainfall during summer and possibly absence of green alder. At the driest sites grow more grass species, mainly small-reed (Calamagrostis spec.). Based on our vegetational surveys of mountain ash forests at the sites mentioned above, we suggest a new sub-association Alno viridi-Sorbetum aucupariae calamagrostietosum prov. of Alno viridi-Sorbetum aucupariae prov. or eventually a new association Calamagrostio-Sorbetum aucupariae prov.