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Aerial sowing stopped the loss of alpine ash (Eucalyptus delegatensis) forests burnt by three short-interval fires in the Alpine National Park, Victoria, Australia
Abstract
Multiple fires in quick succession can cause an abrupt switch from forest to non-forest vegetation in some biomes. A prime example of such type conversion concerns alpine ash forests (Eucalyptus delegatensis subsp. delegatensis), which are endemic to the Australian Alps bioregion. These forests are long lived and can only regenerate following fire disturbance through the release of seed from the tree canopy, but complete regeneration failure of the eucalypt overstorey can occur if immature stands are subsequently reburnt. Wildfires in 2003, 2007 and 2009 burnt over 87% of the Alpine ash forest in Victoria, with some areas being burnt a second or third time within a decade by the 2013 Harrietville-Alpine Bushfire. Using aerial and field surveys we demonstrated that an area burnt two or three times in the Alpine National Park in Victoria would have resulted in loss of alpine ash forest were it not for an aerial sowing program. This sowing program used reduced sowing rates compared to those typically used in forestry silviculture operations in Victoria. Seedling establishment during the first year was lower on sown than natural seedfall areas but fell within the range of acceptable silvicultural stocking rates. Analysis of cohorts of seedlings over their first summer showed mortality was highest in the 2–3 months following emergence, especially during hot dry periods, but there was no difference in mortality rates between artificially and naturally sown areas. While the aerial sowing intervention established a cohort of alpine ash seedlings, the challenge for land managers is to protect these seedlings from wildfires for the next two decades to avoid loss of these forests.
... Aerial seed broadcast, the aerial dispersal of seeds using aircraft, has emerged as a promising approach to ecosystem restoration and land rehabilitation (Sawada et al. 2008;Bassett et al. 2015;Xiao et al. 2015;Novikov and Ersson 2019). Aerial seeding offers several advantages over intensive ground-based planting, including rapid coverage of large areas, feasibility in remote or challenging terrain, reduced biosecurity risk, and decreased labour costs (Bassett et al. 2015;Xiao et al. 2015;Novikov and Ersson 2019). ...
... Aerial seed broadcast, the aerial dispersal of seeds using aircraft, has emerged as a promising approach to ecosystem restoration and land rehabilitation (Sawada et al. 2008;Bassett et al. 2015;Xiao et al. 2015;Novikov and Ersson 2019). Aerial seeding offers several advantages over intensive ground-based planting, including rapid coverage of large areas, feasibility in remote or challenging terrain, reduced biosecurity risk, and decreased labour costs (Bassett et al. 2015;Xiao et al. 2015;Novikov and Ersson 2019). The approach may be particularly useful for rapid revegetation after fires, floods, landslides, or large-scale tree and shrub weed control, as large volumes of seed can be dispersed aerially over damaged areas before exotic weed competitors become dominant (Bassett et al. 2015;Griffiths and McAlpine 2017). ...
... Aerial seeding offers several advantages over intensive ground-based planting, including rapid coverage of large areas, feasibility in remote or challenging terrain, reduced biosecurity risk, and decreased labour costs (Bassett et al. 2015;Xiao et al. 2015;Novikov and Ersson 2019). The approach may be particularly useful for rapid revegetation after fires, floods, landslides, or large-scale tree and shrub weed control, as large volumes of seed can be dispersed aerially over damaged areas before exotic weed competitors become dominant (Bassett et al. 2015;Griffiths and McAlpine 2017). Although aerial seed broadcast depends on the availability of large volumes of seed, long-term cold storage of seed is feasible for many species in New Zealand and other temperate regions globally (Wyse et al. 2023). ...
... Recent evidence suggests that forests dominated by obligateseeder trees in temperate Australia may be at risk of landscape-wide state conversions if high-intensity, short-interval fires become more widespread (Bowman et al., 2014). Management interventions in the form of aerial seed sowing (Bassett et al., 2015) have already been implemented to contain the effects of recent short-interval fires on the distribution of alpine ash (Eucalyptus delegatensis R.T. ...
... Alpine ash is particularly vulnerable to shortening fire intervals through immaturity risk and associated regeneration failure as it requires 15-20 years to reach reproductive maturity (Boland et al., 2006). Two fires within a period of less than 20 years resulted in alpine ash forest conversion to acacia shrublands in isolated locations in the central highlands of Victoria in the 1990s and the 2000s (Bassett et al., 2015;Costermans, 2009), and more broadly across the Australian Alps bioregion in the south-east of Australia (Bowman et al., 2014). Similar conversions of forests to shrublands are known for other obligate-seeder forests in temperate Australia dominated by mountain ash (E. ...
... Previous fire research in alpine ash forests has focussed on empirical investigations of seed dispersal after fire (Morgan et al., 2017), effects of fire severity and wildfire interval on regeneration and fuel characteristics (Bowman et al., 2014;Rodriguez-Cubillo et al., 2020;Gale & Cary, 2021), vegetation structure and fauna (O'Loughlin et al., 2020) and post-fire management (Bassett et al., 2015;Bowman & Kirkpatrick, 1986;Fagg et al., 2013;Grose, 1960). Although some work has considered the direct effects of climate change on the survival of alpine ash (Morgan et al., 2017), no studies have used a multidecadal landscape fire simulation framework to examine effects of changing fire regimes with changing climates on the persistence of alpine ash, despite the acknowledged threat posed by more frequent and severe wildfires (Morgan et al., 2017). ...
Aim
Many species are adapted to a particular fire regime and major deviations from that regime may lead to localized extinction. Here, we quantify immaturity risks to an obligate‐seeder forest tree using an objectively designed climate model ensemble and a probabilistic fire regime simulator to predict future fire regimes.
Location
Alpine ash (Eucalyptus delegatensis) distribution, Victoria, south‐eastern Australia.
Methods
We used a fire regime model (FROST) with six climate projections from a climate model ensemble across 3.7 million hectares of native forest and non‐native vegetation to examine immaturity risks to obligate‐seeder forests dominated by alpine ash (Eucalyptus delegatensis), which has a primary juvenile period of approximately 20 years. Our models incorporated current and future projected climate including fuel feedbacks to simulate fire regimes over 100 years. We then used Random Forest modelling to evaluate which spatial characteristics of the landscape were associated with high immaturity risks to alpine ash forest patches.
Results
Significant shifts to the fire regime were predicted under all six future climate projections. Increases in both wildfire extent (total area burnt, area burnt at high intensity) and frequency were predicted with an average increase of up to 110 hectares burnt annually by short‐interval fires (i.e., within the expected minimum time to reproductive maturity). The immaturity risk posed by short‐interval fires to alpine ash forest patches was well explained by Random Forest models and varied with both location and environmental variables.
Main conclusions
Alpine ash forests are predicted to be burned at greater intensities and shorter intervals under future fire regimes. About 67% of the current alpine ash distribution was predicted to be at some level of immaturity risk over the 100‐year modelling period, with the greatest risks to those patches located on the periphery of the current distribution, closer to roads or surrounded by a drier landscape at lower elevations.
... Directly sowing seed into the field is a particularly convenient methodif an ex situ seed bank is availablebecause it can be applied quickly and cheaply. For example, aerial sowing was rapidly deployed in the Victorian Alps after repeat fires destroyed the natural seedbank of Eucalyptus delegatensis forests (Bassett et al., 2015). However, transplanting often has higher success rates, because transplant survivorship exceeds that of new germinants in the field (Palma and Laurance, 2015). ...
... For some species, the time between a fire and a restoration intervention is a crucial. For instance, restoring Eucalytpus delegatensis forest requires sowing seeds in the first winter after a fire, while a suitable ash bed still exists (Bassett et al., 2015). Conversely, other plants cannot establish immediately, and need pioneer species to create suitable conditions. ...
Introduction
Pencil pine ( Athrotaxis cupressoides ) is an iconic, paleoendemic tree restricted to historic fire refugia in Tasmania’s western mountains. Anthropogenic climate change is increasingly exposing these areas to wildfire. Given that pencil pines have little capacity to recover from fire, and show scarce natural recruitment across their core range, they will be lost from many areas without interventions to restore population viability to burnt stands.
Methods
We conducted a large-scale field study targeting pencil pine stands burnt in recent (2016) and historic (1960) fires. Using small (0.5 m ² ) experimental plots distributed across a range of topography and vegetation, we trialled three interventions: i) protecting groups of naturally germinated seedlings from herbivores in situ (35 plots); ii) introducing seeds via multiple sowing methods (300 plots); and iii) transplanting tube stock propagated from seed or cutting material, with and without herbivore protection (1007 plots).
Results
We found that protecting natural germinants from herbivores did not prevent seedling mortality over 2.5 years, and sowing interventions largely failed. Most transplants exposed to herbivores failed to establish after 1.5 years, but establishment rates were high with herbivore exclusion, indicating strong predation by native macropod herbivores. Transplant establishment also varied with fine-scale topography, with the best outcomes in well-drained and Sphagnum dominated positions, and the worst outcomes in poorly-drained positions, suggesting young pencil pines are sensitive to waterlogging. Transplant establishment rates varied little between recently and historically burnt sites, and were insensitive to how plants were propagated.
Discussion
In summary, transplanting tube stock with herbivore protection is a promising method for restoring burnt pencil pine stands, and establishment rates can be improved by selecting favourable planting positions at fine scales. Our findings suggest pencil pine stands burnt decades previously are suitable for restoration. Managers seeking to conserve pencil pines may begin restoring both historically and recently burnt stands, alongside protecting unburned stands from fire. Interventions should be refined through adaptive management, including re-surveys of this long-term trial.
... In Victoria in 2003, several stands were fire-killed that had either been burned twice or logged in the preceding 20 years. These were predicted to mostly return as shrublands dominated by Acacia species, and a major effort was undertaken to reseed many of these areas, at a cost of around $1000 per hectare (Bassett 2013;Bassett et al. 2015;Fagg et al. 2013). However, it is unclear how much of the affected areas had no Eucalyptus delegatensis regeneration in the absence of aerial seeding. ...
... The resprouting ability of eucalypt species other than Eucalyptus delegatensis may lead to a transition in composition and structure from fire-killed Eucalyptus delegatensis stands to more fire tolerant mixed eucalypt stands, but whether this happens naturally or needs to be facilitated is an open question (Colloff et al. 2016;Doherty et al. 2017b). Although fire-killed Eucalyptus delegatensis stands with little or no natural regeneration have been successfully re-seeded in some parts of the Victorian alps (Bassett et al. 2015), such stands remain vulnerable to repeated fire despite a large financial re-investment in re-seeding. Additionally, given the potential for differential performance of the species across its elevational range based on existing genotypic variation, we suggest a cautionary approach is warranted to broad area re-seeding until more is known about the mixing of Eucalyptus delegatensis genotypes. ...
Eucalyptus delegatensis R.T. Baker subsp. delegatensis (Alpine Ash) is the dominant canopy species in large areas of montane forest in the Australian Alps. As the species is killed by high severity fire, minimal intervals between fire are required for the species to germinate and to reach reproductive maturity to ensure stand persistence. In 2003 and again in 2020, extensive high severity fires occurred in southeastern Australia. These burnt through large tracts of Kosciuszko National Park in New South Wales, where the 9309 ha of Eucalyptus delegatensis that burnt at high severity in both 2003 and 2020 is of particular management concern. In 2021, using an existing array of Eucalyptus delegatensis dominated monitoring plots set up between 2008 and 2013, we undertook a survey of seedling regeneration in plots burnt either at low severity in 2003 and high severity in 2020 or burnt at high severity in both 2003 and in 2020. We found a highly significant tendency for greater recruitment in plots only burnt at high severity 2020 as compared with plots burnt at high severity in both 2003 and 2020. Despite this significant difference, there was still robust recruitment in the plots burnt twice at high severity and there were no plots where recruitment failure was observed. In mixed stands with other re-sprouting eucalypt species present, the overwhelming majority of seedlings post-fire were of Eucalyptus delegatensis. For plots burnt twice at high severity, greater recruitment of Eucalyptus delegatensis occurred in mid-elevation stands, as compared to stands at the lower and upper limits of the elevational range of the species within Kosciuszko National Park. Despite the downward trend in Eucalyptus delegatensis seedling recruitment with short inter-fire intervals, the 17 year interval between 2003 and 2020 allowed early maturing saplings to establish a viable canopy seed bank. Monitoring the growth and survival of the post-2020 cohort of seedlings will be critical to inform appropriate fire management. Our dataset makes a significant contribution to understanding recruitment and survival in eucalypts post-fire in the Australian Alpine Bioregion and it will be important to continue to document the time to first flowering and fruiting of individuals in fire affected stands and to track the proportion of saplings reaching reproductive maturity over time, to gauge stand vulnerability to further high severity fires over coming decades. Cunninghamia (2023) 23: 055-066
... In recent years, fires have destroyed large parts of forests in catchments crucial for the provision of freshwater resources, such as in California (e.g., Gutierrez et al., 2021;Maina & Siirila-Woodburn, 2020) and southern and eastern Australia (e.g., Canadell et al., 2021;Feikema et al., 2013;Lindenmayer & Taylor, 2020). Some of these forests are highly susceptible to frequent fires and if fire occurs more frequently due to global climate change than the age of maturity of the trees, there is an irreversible change in forest type, structure, and function (Bassett et al., 2015;Bowd et al., 2018;Bowman et al., 2016). The destruction of mature forests by fire and the subsequent regrowth of young forests can alter the exchange of energy, water, and carbon at the land surface (Liu et al., 2019;Seidl et al., 2014) and potentially lead to changes in evapotranspiration (ET) and thus discharge and water yield from these forested catchments (Bond-Lamberty et al., 2009;Kuczera, 1987;. ...
... Additionally, higher frequency of forest fires due to climate change (Canadell et al., 2021) decreases not only forest age, but could also lead to changes in forest structure and species composition (Hill & Field, 2021), which in turn could alter canopy function. For example, Eucalyptus regnans trees take around 20 years to reach reproductive maturity and fires occurring more frequently than that will likely lead to a change in forest type (Bassett et al., 2015;Bowd et al., 2018;Bowman et al., 2016). A decrease in LAI and a reduction of vegetation cover were common explanations for the decrease in ET and increase in Q found in previous research in other parts of the world (e.g., Bart et al., 2016;Boisramé et al., 2019;Bond-Lamberty et al., 2009;. ...
Wildfires are increasing in frequency, intensity, and extent globally due to climate change and they can alter forest composition, structure, and function. The destruction and subsequent regrowth of young vegetation can modify the ecosystem evapotranspiration and downstream water availability. However, the response of forest recovery on hydrology is not well known with even the sign of evapotranspiration and water yield changes following forest fires being uncertain across the globe. Here, we quantify the effects of forest regrowth after catastrophic wildfires on evapotranspiration and runoff in the world's tallest angiosperm forest ( Eucalyptus regnans ) in Australia. We combine eddy covariance measurements including pre‐ and post‐fire periods, mechanistic ecohydrological modeling and then extend the analysis spatially to multiple fires in eucalypt‐dominated forests in south‐eastern Australia by utilizing remote sensing. We find a fast recovery of evapotranspiration which reaches and exceeds pre‐fire values within 2 years after the bushfire, a result confirmed by eddy covariance data, remote sensing, and modeling. Such a fast evapotranspiration recovery is likely generalizable to tall eucalypt forests in south‐eastern Australia as shown by remote sensing. Once climate variability is discounted, ecohydrological modeling shows evapotranspiration rates from the recovering forest which reach peak values of +20% evapotranspiration 3 years post‐fire. As a result, modeled runoff decreases substantially. Contrary to previous research, we find that the increase in modeled evapotranspiration is largely caused by the aerodynamic effects of a much shorter forest height leading to higher surface temperature, higher humidity gradients and therefore increased transpiration. However, increases in evapotranspiration as well as decreases in runoff caused by the young forest are constrained by energy and water limitations. Our result of an increase in evapotranspiration due to aerodynamic warming in a shorter forest after wildfires could occur in many parts of the world experiencing forest disturbances.
... These may include collections of seed or vegetative material for various conservation purposes, including restoration and translocation, reintroductions and establishing seed orchards (e.g. Bassett et al. 2015;Commander et al. 2018;Martyn Yenson et al. 2021, Box 15). For some species, emergency germplasm collection may be needed (Martyn Yenson et al. 2021), for example because of post-fire impacts of myrtle rust. ...
... In such cases, future restoration management may be needed (e.g. direct seeding of canopy dominant E. delegatensis;Bassett et al. 2015). Q T. D.Auld et al. ...
Globally, many species and ecosystems are experiencing landscape-scale wildfires (‘megafires’) and these events are predicted to increase in frequency and severity as the climate warms. Consequently, the capability to rapidly assess the likely impacts of such large fires and identify potential risks they pose to the persistence of species and ecosystems is vital for effective conservation management. In this review, we propose novel frameworks to identify which plant species and ecosystems are most in need of management actions as a result of megafires. We do this by assessing the impacts of a fire event on plants and ecosystems in the context of the whole fire regime (current fire event combined with recent fire history) and its interactions with other threatening processes, rather than simply considering the amount of habitat burnt. The frameworks are based on a combination of key species’ traits related to mechanisms of decline, components of the fire regime that are most likely to have adverse impacts on species or ecosystem recovery, and biotic and environmental factors that may amplify fire impacts or pose barriers to post-fire recovery. We applied these frameworks to guide management priorities and responses following the extensive 2019/2020 fires in southern Australia, and we illustrate their application here via a series of worked examples that highlight the various mechanisms of post-fire decline the frameworks address. The frameworks should be applicable to a broader range of fire-prone biomes worldwide. Our approach will (1) promote the development of foundational national datasets for assessing megafire impacts on biodiversity, (2) identify targeted priority actions for conservation, (3) inform planning for future fires (both prescribed burning and wildfire suppression), and (4) build awareness and understanding of the potential breadth of factors that threaten plants and ecosystems under changing fire regimes.
... McColl-Gausden et al. (2022) provide a case study of immaturity risk for the obligate seeding Alpine Ash (Eucalyptus delegatensis) in south-eastern Australia, a region that has undergone a substantial increase in fire activity in recent decades Fairman et al., 2015). Alpine ash requires 15-20 years to reach reproductive maturity, so if multiple fires occur within a 20-year window, alpine ash forests can be converted into shrublands (Bassett et al., 2015). Similar state shifts have been described in North America following the loss of obligate-seeding conifers (Coop et al., 2020). ...
... In terms of reversing fire-induced state shifts, some ambitious projects have already been attempted. Bassett et al. (2015) aerially sowed ~2,000 ha of alpine ash forests that had failed to regenerate after frequent fires in southern Australia, demonstrating that such an intervention could create a cohort of seedlings where interval squeeze has obliterated natural seed stores. The capacity to scale up such efforts from thousands to tens or hundreds of thousands of hectares, and the wisdom of doing so-of attempting to retain an ecological system in an artificial state while the niche of its dominant species disappears-requires careful consideration. ...
... Over the past 50 years this has led to an emphasis on relatively intensive silvicultural prescriptions such as clear-felling in southeastern Australia. After harvesting, a site is burnt or mechanically disturbed and then seed is aerially sown (~200,000 seeds per ha) to ensure successful post-disturbance regeneration in young Eucalyptus forests and to avoid a shift to non-eucalypt-vegetation types (Bassett et al., 2015). Within 12-18 months of aerial sowing, each coupe is surveyed to determine if there is sufficient regeneration. ...
... This may make these forests less resilient to future wildfires (Rodman et al., 2020), which are predicted to occur more frequently in the montane forests of southeastern Australia (Keenan and Nitschke, 2016). This not only has implications for achieving a key objective of sustainable forest management but also for the future success of post-fire sowing of E. regnans and E. delegatensis (see Bassett et al., 2015) in a landscape of more frequent fire. ...
In the forested landscapes of southeastern Australia, bushfires and timber harvesting are the primary catalysts for regeneration in Eucalyptus regnans, E. delegatensis, and high elevation mixed species (HEMS) forests. Quantifying the role of climate, topography and edaphic conditions on plant regeneration is important for understanding current and future risks of climate change. In this study, we investigated the post—disturbance regeneration dynamics in these forests. We sought to determine the direct impact of climate variability on regeneration and the interactive effects of climate, topography, and edaphic factors on the regeneration success of Eucalyptus. Data was collated from regeneration surveys conducted in 881 coupes, totaling ~55,000 ha of forest harvested and regenerated between 2004–2012. The time—period analysed included the Millennium Drought, an intense and prolonged drought that lasted from 1996 to 2010. To test the influence of climatic, topographic, and edaphic variables on the occurrence and abundance of Eucalyptus regeneration, we used machine learning models. We found that regeneration success was closely tied to the timing of the Millennium Drought. Between 2004 and 2005 Eucalyptus seedlings occurred in less than 50% of survey plots across all three forest types. Declines in regeneration during the period of drought were greater in E. regnans and E. delegatensis than HEMS forests, suggesting that regeneration in the HEMS forests is more resistant to drought. We found that seasonal precipitation and temperature had the greatest influence on regeneration success of Eucalyptus. Responses varied by species, however autumn precipitation had the strongest influence on abundance of regeneration of E. regnans and E. delegatensis, while summer temperature was more important for HEMS species. Our findings highlight the importance of seasonal and annual climate variability on Eucalyptus regeneration and portend potential declines in regeneration success in a warmer and drier future for E. regnans and E. delegatensis.
... In temperate Eucalyptus forests, fire severity assessments are increasingly being used by fire ecologists to understand the impacts of intense fires, and the legacy effects of land use such as logging and prescribed burning [6,43,44]. However, the satellite-based approach remains nascent in these ecosystems and has never been applied in Tasmania. ...
... Fire severity assessments are increasingly being used by fire ecologists to understand the impacts of intense fires, and the legacy effects of prescribed burning in temperate Eucalyptus forests [6,43,44]. This study is the first ever to map fire severity patterns for the island state of Tasmania. ...
Fire severity is an important characteristic of fire regimes; however, global assessments of fire regimes typically focus more on fire frequency and burnt area. Our objective in this case study is to use multiple lines of evidence to understand fire severity and intensity patterns and their environmental correlates in the extreme 2013 Forcett-Dunalley fire in southeast Tasmania, Australia. We use maximum likelihood classification of aerial photography, and fire behavior equations, to report on fire severity and intensity patterns, and compare the performance of multiple thresholds of the normalised burn ratio (dNBR) and normalized difference vegetation index (dNDVI) (from pre- and post-fire Landsat 7 images) against classified aerial photography. We investigate how vegetation, topography, and fire weather, and therefore intensity, influenced fire severity patterns. According to the aerial photographic classification, the fire burnt 25,950 ha of which 5% burnt at low severities, 17% at medium severity, 32% at high severity, 23% at very high severities, while 22% contained unburnt patches. Generalized linear modelling revealed that fire severity was strongly influenced by slope angle, aspect, and interactions between vegetation type and fire weather (FFDI) ranging from moderate (12) to catastrophic (>100). Extreme fire weather, which occurred in 2% of the total fire duration of the fire (16 days), caused the fire to burn nearly half (46%) of the total area of the fireground and resulted in modelled extreme fireline intensities among all vegetation types, including an inferred peak of 68,000 kW·m⁻¹ in dry forest. The best satellite-based severity map was the site-specific dNBR (45% congruence with aerial photography) showing dNBR potential in Eucalyptus forests, but the reliability of this approach must be assessed using aerial photography, and/or ground assessment.
... A number of studies in the past decade have illustrated a growing immaturity risk for fire-killed tree species (i.e. fire occurring before populations have produced sufficient seeds for self-replacement; Keeley et al. 1999) based on a shortening of fire intervals due to a combination of global environmental change drivers, including for Californian conifers (Agne et al. 2022), Mediterranean Basin pines (Espelta et al. 2008), western USA conifers , boreal conifers (Brown and Johnstone 2012;Whitman et al. 2019), and Australian eucalypts (Bassett et al. 2015;von Takach Dukai et al. 2018). More recently, evidence of increased recruitment failure after fire has emerged, with increasing frequency of post-fire drought implicated as a major driver, particularly in the western USA (Harvey et al. 2016;Stevens-Rumann et al. 2018;Davis et al. 2019;Hansen and Turner 2019). ...
Background
Mediterranean-type ecosystems (MTEs) are experiencing declining rainfall, increasing temperature, and shifting fire regimes as climate changes. While changes in fire regimes and post-fire recruitment are widely reported, evidence for changing plant demographic rates is limited.
Aims
We hypothesised increased time to maturity and decreased serotinous seed stores available for post-fire recruitment due to declining rainfall over recent decades for two fire-killed serotinous shrubs of south-east Australian MTEs, Hakea decurrens and Banksia ornata.
Methods
Fruit and cone production for populations across time since fire chronosequences were measured in the same regions in the 1990s and in 2017.
Key results
Estimated time to 50% maturity increased from 3–15 years and 6–15 years for H. decurrens and B. ornata, respectively, while estimated canopy seed stores were 90% and 50% lower in 2017 than in the 1990s.
Conclusions
Delayed reproductive maturity and decreased total seed stores were significantly related to decreasing rainfall received by 2017 populations over their lifetimes (5–17% less than for stands in the 1990s).
Implications
Shifts in inter-fire rates of seed production and storage, combined with changes to fire regimes and post-fire recruitment conditions due to climate change may already threaten the persistence of some species.
... A key outcome of this research is the identification of areas where E. regnans and E. delegatensis has failed to regenerate following timber harvesting and has been displaced by Acacia spp. The timely implementation of sowing and silviculture practices has been demonstrated to prevent the extirpation of obligate-seeder Eucalyptus spp. in successively disturbed areas (Bassett et al., 2015). The findings and approach could help understand the impact that logging and changes in fire regimes can have on the vegetation structure of E. regnans and E. delegatensis dominant forest and provide a valuable tool for identifying areas at risk to state changes under future climate scenarios and fire return intervals. ...
... In Australia's montane forests, fire frequency and severity has increased over the last two decades (Bowman et al., 2014;Zylstra, 2018). Theoretical and field-based studies indicate obligate seeder forests are at risk of decline and potential forest-type conversion with shortening fire intervals (Bowman et al., 2014;Bassett et al., 2015;Fairman et al., 2016;McColl-Gausden et al., 2020). High elevation mixed species forests in contrast contain a variety of resprouting species and are thought to be more resilient to frequent severe fire (Burrows, 2013;Clarke et al., 2015;Fairman et al., 2017;Collins et al., 2021). ...
... This will in part involve assessing fire impacts and identifying when interventions will be required to assist recovery towards defined target ecosystems (Gann et al. 2019). Aerial sowing of seeds has been used to restore alpine ash to repeatedly burned areas in Victoria's Alpine National Park (Bassett et al. 2015). Similar measures, which are reliant on comprehensive seed banks (https://www.abc.net.au/ ...
... From some of these experimental studies, Kallander and Berry (1953) highlighted the key factors to be considered for purpose of determining the adaptability to aerial seeding, namely: size of area, seed source, natural stocking, cover, soil condition, degree of burn, exposure and slope. It has also emerged that success in direct seeding requires adequate description of the area targeted for seeding, the sowing or application equipment (helicopter or fixed-wing aircraft), timing and seeding rate (Scott, 1970;Bassett et al., 2015). ...
The use or deployment of aerial seeding technology in forestry has shown to be efficient, rapid, and most suitable for restoration of large degraded and inaccessible areas. The technology is relatively cheaper compared to conventional methods of restoration. Although aerial seeding has been widely used globally in forestry, its application is comparatively new in Kenyan forestry. This paper reviews selected experiences from countries that pioneered the use of aerial seeding in restoring large degraded forestlands and highlights key requirements for successful aerial seeding programs. Literature shows that the use of aerial seeding in forestland restoration dates back in 1950s with reports showing moderate to high success rate in USA, Canada, Russia, Australia, New Zealand, China and India. Success of aerial seeding is largely determined by interaction of factors such as seed characteristics, timing of seeding, site conditions or micro-site environment. Competition from surrounding vegetation, and seed predation affect the efficiency of aerial seeding negatively. The paper concludes that aerial seeding technology is efficient, cost effective and therefore suitable for use in the restoration of the expansive degraded forests in Kenya.
... To ensure Australian forests retain their ecological key functions in the future it is necessary to evaluate how different tenure and protection status might impact forest resilience to fire. Of particular interest is recovery duration, as some forested ecosystems rely on a certain period of recovery before re-developing the ability to reproduce [13]. This study aims to explore the relationship between different forest management regimes and the length of post-fire recovery in southeast Australia. ...
Research Highlights: We used Landsat time series data to investigate the role forest tenure and protection status play in the recovery of a forest after a fire. Background and Objectives: Changing fire regimes put forests in southeast Australia under increasing pressure. Our investigation aimed to explore the impact of different forest management structures on a forest’s resilience to fire by looking at the post-fire recovery duration. Materials and Methods: The analysis included a total of 60.6 Mha of land containing 25.4 Mha of forest in southeast Australia. Multispectral time series data from Landsat satellites and a local reference dataset were used to model attributes of disturbance and recovery over a period of 33 years. Results: Protected public forest spectrally recovered 0.4 years faster than protected private forest. No other significant effects in relation to different tenure and protection status were found. Climatic and topographic variables were found to have much greater influence on post-fire spectral recovery. Conclusions: Protected area status in public forests resulted in slightly faster recovery, compared with the private protected forest estate. However, factors outside the control of land managers and policy makers, i.e., climatic and topographic variables, appear to have a much greater impact on post-fire recovery.
... Rapid climate change and increased occurrence of extreme fire weather has increased fire activity in temperate forests, particularly in the western United States and eastern Australia (Abatzoglou and Williams, 2016;Abram et al., 2021;Heidari et al., 2021), possibly to the extent that biomes may be shifting from forests to grasslands (Bassett et al., 2015), with consequences for forest C carrying capacity. ...
Disturbance trends over recent decades indicate that climate change is resulting in increased fire severity and extent in Australia's temperate Eucalyptus forests. As disturbance cycles become shorter and more severe, empirical measurements are required to identify potential change in forest carbon (C) stock and emissions. However, such estimates are rare in the literature.
The 2019–2020 wildfires burnt through 6 to 7 million ha of mainly medium and open Eucalyptus forest in south-east Australia, with top down emission estimates ranging from 97 to 130 tonnes CO2 ha⁻¹. Study sites that had been assessed for all aboveground C pools prior to the wildfires, were burnt in January 2020 by wildfire that varied in severity. Here we quantify the impact of high and low/moderate fire severities on tree mortality, C loss and C redistribution and assess implications for future C storage in these temperate Eucalyptus forests.
Higher fire severity resulted in greater overstorey tree mortality but not understorey or loss of dead standing trees than in low/moderate severity fires. High severity fires combusted almost twice as much C from live trees (42 Mg C ha⁻¹) as low/moderate severity fires (25 Mg C ha⁻¹), while C loss from dead standing trees was similar among fire severity classes (average 17 Mg C ha⁻¹). Total aboveground C lost across study sites was 42 Mg C ha⁻¹ for high and 47 Mg C ha⁻¹ for low/moderate severity, with an average of 45 Mg C ha⁻¹ equivalent to 15 % (high severity) and 14 % (low/moderate severity) of AGC.
Extrapolating our findings to other tall to medium open Eucalyptus forests across Victoria revealed that 37.33 ± 12.25 Tg C (mean ± s.e.) or 152 ± 50 Mg CO2 ha⁻¹ was lost to the atmosphere from the 0.9 million ha of these productive forests, equating to about 20 % of Australia's total net annual emissions.
... Much of the Australian Alps bioregion has had recent increases in fire frequency, far greater than the historical average (Bassett et al. 2015). Positive flammability feedback dynamics have been quantified in the Australian Alps, demonstrating that recently burned forests are more flammable than mature forests (Zylstra 2013(Zylstra , 2018. ...
Early and ongoing monitoring of post-fire recovery dynamics is critical for understanding the ecological resilience of forests. The unprecedented scale of Australia’s Black Summer of 2019–2020 poses a significant challenge for post-fire recovery monitoring. Remote sensing is the only practical way to undertake broad-scale analysis of post-fire recovery dynamics. We used Sentinel 2 satellite imagery to compare pre-fire and 1-year post-fire Normalised Burn Ratio (NBR) values. A strong positive trend in the return of vegetation was indicated where post-fire values met or exceeded 80% of the pre-fire NBR value. Our assessment highlighted locations where early recovery responses were divergent from trends in the surrounding areas. Overall, there was a strong spectral recovery across the 2019–2020 south-east Australia fire extent, with more than 50% of the total burned area showing greater than 80% spectral recovery after 1 year. However, several areas where ecosystem resilience may be threatened were identified, including fire-sensitive ecosystems and severely drought-impacted regions. Our results demonstrated biogeographic variation in the effect of fire severity on post-fire spectral recovery, with little effect of severity on spectral recovery observed in the north-east, but much stronger effects in the south. Our study highlights further research for prioritisation as part of adaptive land management programs.
... Rapid development of a large canopy seed bank in high-density stands suggests that high establishment densities exhibited by serotinous conifers (Verkaik and Espelta 2006;Harvey and Holzman 2014) represent a resilience mechanism to short-interval fires. While serotinous populations may be able to persist at lower densities following a single short-interval severe fire (Keeley et al. 1999;Turner et al. 2019), they are unlikely to withstand recurrent short-interval fire activity Bassett et al. 2015). Demographic rates must be assessed in the context of the expected shortening of the fire-free interval to understand when erosion of serotinous forest resilience to fire may occur. ...
The resilience of serotinous obligate-seeding plants to fire may be compromised if increasing fire frequency curtails time available for canopy seed bank accumulation (i.e., immaturity risk), but how various drivers affect seed availability at the time of fire is poorly understood. Using field data from California closed-cone pine (Pinus attenuata and P. muricata) stands, we assess two critical demographic processes during the inter-fire period—reproductive capacity and mortality. At tree- and stand-levels, we test how these processes are affected by stand age and are mediated by biotic and abiotic factors. We found that stand age was the key driver of reproductive capacity; older stands had a greater proportion of reproductively mature individuals and greater closed cone density. Stand density mediated the effect of age; greater stand density resulted in greater closed cone density and a lower proportion of reproductively mature individuals, but reproductive capacity in low- and high-density stands converged over time. Increased moisture stress reduced the stand-level proportion reproductively mature trees but had no effect on closed cone density. Mortality was strongly associated with density-dependent thinning and increased in stands with high moisture stress. Reproductive capacity began to increase sharply 10 years post-fire and by 20 years immaturity risk was low. However, prior to 20 years, low-density stands with high moisture stress may be more susceptible to immaturity risk. Understanding these relationships is critical to predicting serotinous population persistence under changing climate and disturbance conditions.
... Where national forest inventory data include stem density and quadratic mean diameter, the proposed model could be used to map seed crops across landscape scales, potentially with spatial and temporal refinements using aerial assessment of flowering intensity (Incoll, 1975) and adjustment for rainfall variation (Abrahamson and Layne, 2003;Bassett, 2014). Detailed seed crop predictions could support the planning of seed collection, an essential task in forests where occasional short fire intervals threaten seed supply for natural regeneration (Bassett et al., 2015). Further potential applications include the planning and management of seed orchards, where the level of tree maturity is an important consideration (Longman, 1987), and predicting the effect of thinning treatments, by altering the separate tree density term in the model (c.f. ...
Quantifying mean annual tree seed production is important for conservation and forestry applications, but its estimation remains a substantial challenge. Interspecies variation in seed production is often expressed as a trade-off between seed size and seed number, forming a key component of established models of mean annual seed production in forest stands. In this study we improved on these models by quantifying additional effects from accessory costs and reproductive maturity status, using data from temperate-zone Eucalyptus species to assess model performance.
Firstly, by evaluating a range of reproductive traits, we found that seed rain density was more closely associated with ‘fruit cost per seed’ measures than seed size measures. For the most common measure of seed rain density (based on direct observations of free seed fall), woody capsule surface area per viable seed explained 70% of observed variation, while seed mass explained only 28% (n = 16 species).
Secondly, an existing model based on seed mass, tree size and tree density was extended to include a stand maturity function, and to use alternative reproductive traits. For a smaller dataset with long-term observations and detailed stand measurements, the proportion of variance explained by the extended model ranged from 81 to 98% depending on trait selection (mean = 93%), with published models explaining less variance (75–83%, mean = 80%).
By reframing interspecies variation in seed production as a trade-off between seed cost and seed number, we found evidence that investment in heavy fruit structures may represent a substantial constraint on seed output among forest stands from a common genus and region, although our results must be considered somewhat preliminary, given the small number of species examined. We have also developed an enhanced predictive model, which could be used with stand-level models for tree size and tree density to improve predictions of mean annual forest seed production in landscape simulations.
... This may reflect the fact that fuel loads were still low following the 2003 fires, where over half of all the forest in the bioregion was burnt. The low rainfall for several years after 2003 may have impeded recovery in the region, which was found to be much longer than elsewhere (9.5 years on average), although high-altitude species such as alpine ash (Eucalyptus delegatensis) are, in general, slower to recover than many other eucalypts (Bassett et al., 2015). In the Victorian alpine region, longer spectral recovery after wildfire has also been observed (Hislop et al., 2019b). ...
Comprehensive and robust estimations of forest disturbance over time are lacking in many parts of the world. In recent years, Landsat satellite data has been used extensively to retrospectively map forest disturbance across several decades. Human interpretation of Landsat time series, in association with ancillary data, has emerged as an effective and affordable way to collect reference data, which is often used to calibrate and validate disturbance models. If the reference data is collected using a robust probability sampling protocol, estimates of disturbance can be derived directly from the reference dataset using simple calculations. In this paper, we present the results of a reference data project in New South Wales, Australia, undertaken to characterise three decades of canopy disturbance across 13 Mha of predominantly native eucalypt forests. Our results indicate that disturbance is a frequent occurrence, with 70% of the forest disturbed during the last 33 years and around 35% experiencing two or more disturbances. The most common disturbance agent was wildfire, however, most wildfire disturbance occurred in few years, with over 4 Mha burnt in 2019–20 alone. The second most common disturbance agent was drought, which together with fire, was strongly influenced by low rainfall in the preceding years. Forest recovery was often quite rapid following disturbance, particularly in the event of increased rainfall. In this study, we demonstrate the value of collecting information in a systematic and comprehensive framework, which can be used to address numerous monitoring questions regarding forest canopy disturbance.
... • Actively managing dry forests to the north and west of these forests to enable fire suppression and control under severe conditions and thereby reduce the likelihood of fires moving into wet forests • Maintaining capacity to rapidly suppress and extinguish fires, particularly those starting in drier forests under extreme fire weather conditions that will spread into wet forests, by maintaining roads and access tracks and firefighting capability in or near the forest for rapid early detection and response • Thinning in even-aged regrowth to accelerate the growth of residual trees and reduce the likelihood that they will be killed by bushfire • Using alternative silvicultural practices to create more variable stand structures and maintain larger trees as seed sources across the landscape • Maintaining adequate seed stocks and technical capacity to regenerate severely burnt or reburnt areas by reseeding (Ferguson 2009;Bassett et al. 2015). ...
In the summer of 2019/20, bushfires of unprecedented scale in south-eastern Australia focused attention on how forest management might have affected their risks and impacts. Some argued that the severity and extent of these fires were made worse by timber harvesting and associated forest management and that harvesting in native forests should cease as a means for reducing fire risk. Little evidence has been presented to support these contentions. This article reviews evidence for the relationship between harvesting and fire extent and severity from these fires. The proportion of forested conservation reserves burnt in these fires was similar to that for public forests where timber harvesting is permitted, and the proportion of forest burnt with different levels of fire severity was similar across tenures and over time since timber harvest. Recent analysis of the areas burnt in 2019/20 indicated that the extent and severity of the fires was determined almost entirely by three years of well-below-average rainfall (leading to dry fuels across all vegetation types), extreme fire weather conditions and local topography and that past timber harvesting had negligible or no impact on fire severity. Three major inquiries into the fires made no recommendations regarding the impact of timber harvesting on fire risk. We argue that policy proposals to mitigate fire risk and impacts should be evidence-based and, to avoid the cognitive bias associated with expert opinions, should integrate the multiple perspectives of traditional Indigenous knowledge, the experience of local and professional fire managers, and the breadth of evidence from bushfire research. Together, these perspectives should inform strategies for reducing bushfire impacts and increasing forest resilience and community safety.
... Frequent high-severity fires can cause a substantial reduction in tree density in forests dominated by both resprouting and obligate-seeding species [12][13][14] . For instance, three fires in quick succession in the early twenty-first century caused the demographic collapse of an obligate-seeder-dominated Eucalyptus forest 15 . ...
The 2019–20 wildfires in eastern Australia presented a globally important opportunity to evaluate the respective roles of climatic drivers and natural and anthropogenic disturbances in causing high-severity fires. Here, we show the overwhelming dominance of fire weather in causing complete scorch or consumption of forest canopies in natural and plantation forests in three regions across the geographic range of these fires. Sampling 32% (2.35 Mha) of the area burnt we found that >44% of the native forests suffered severe canopy damage. Past logging and wildfire disturbance in natural forests had a very low effect on severe canopy damage, reflecting the limited extent logged in the last 25 years (4.5% in eastern Victoria, 5.3% in southern New South Wales (NSW) and 7.8% in northern NSW). The most important variables determining severe canopy damage were broad spatial factors (mostly topographic) followed by fire weather. Timber plantations affected by fire were concentrated in NSW and 26% were burnt by the fires and >70% of the NSW plantations suffered severe canopy damage showing that this intensive means of wood production is extremely vulnerable to wildfire. The massive geographic scale and severity of these Australian fires is best explained by extrinsic factors: an historically anomalous drought coupled with strong, hot dry westerly winds that caused uninterrupted, and often dangerous, fire weather over the entire fire season. Geospatial analysis of forest canopy damage in over half the area burned in the 2019–20 southeast Australian wildfires shows that spatial factors and weather determine burning severity much more than past logging and wildfire disturbance.
... If local adaptation in forest trees such as mountain ash occurs in such a manner, there are large implications for planning restoration and assisted migration strategies. For example, seeds are currently being collected at increasingly large volumes across south-eastern Australia because frequent wildfires and resulting failure of natural regeneration means that large areas are requiring artificial regeneration (Bassett et al., 2015). With most alleles present in the seedbank at most sites, collection of locally-sourced seeds or seeds from sites with matching environmental conditions would not necessarily result in a greater level of local adaptation than using seeds collected from near-random locations, meaning there would be little benefit to such resource-intensive strategies. ...
Understanding local adaptation is critical for conservation management under rapidly changing environmental conditions. Local adaptation inferred from genotype-environment associations may show different genomic patterns depending on the spatial scale of sampling, due to differences in the slope of environmental gradients and the level of gene flow. We compared signatures of local adaptation across the genome of mountain ash (Eucalyptus regnans) at two spatial scales: a species-wide dataset and a topographically-complex sub-regional dataset. We genotyped 367 individual trees at over 3700 single-nucleotide polymorphisms (SNPs), quantified patterns of spatial genetic structure among populations, and used two analytical methods to identify loci associated with at least one of three environmental variables at each spatial scale. Together, the analyses identified 549 potentially adaptive SNPs at the sub-region scale, and 435 SNPs at the range-wide scale. Thirty-nine genic or near-genic SNPs, associated with 28 genes, were identified at both spatial scales, although no SNP was identified by both methods at both scales. We observed that non-genic regions had significantly higher homozygote excess than genic regions, possibly due to selective elimination of inbred genotypes during stand development. Our results suggest that strong environmental selection occurs in mountain ash, and that the identification of putatively adaptive loci can differ substantially depending on the spatial scale of analyses. We also highlight the importance of multiple adaptive genetic architectures for understanding patterns of local adaptation across large heterogenous landscapes, with comparison of putatively adaptive loci among spatial scales providing crucial insights into the process of adaptation.
... Hence, fire intervalthe time between firesis particularly important for obligateseeding species: if fire occurs before seed is produced, and there is no soil seedbank, then the species may be extirpated from the site (Keith 1996). For example, multiple fires in the central highlands of Victoria in the 2000s meant that a large area of Eucalyptus delegatensis was burnt while immaturethousands of hectares have since been artificially re-sown (Bassett et al. 2015). Fire frequency can also affect resprouting capacity; mortality rates of the resprouting species Eucalyptus pauciflora were increased by 50% when the species was burnt by three short-interval wildfires (Fairman et al. 2017). ...
Changing climate is predicted to result in increased frequency and size of wildfires in south-eastern Australia. With increasing area burnt there is increased potential for entire species distributions to be burnt in a single fire event. This is particularly the case for range-restricted threatened species. Eucalyptus canobolensis (L.A.S.Johnson & K.D.Hill) J.T.Hunter is restricted to Mount Canobolas, New South Wales, Australia. In 2018, the majority of the E. canobolensis population was burnt by wildfire. One-year post-fire, we measured recruitment, resprouting and mortality of E. canobolensis. At higher fire severities, smaller trees were more likely to resprout from their bases only, as their stems were killed (i.e. ‘top kill’). Seedling regeneration only occurred in burnt plots. Our study demonstrates that E. canobolensis has a fire response typical of many eucalypts, characterised by seedling recruitment and larger trees resprouting epicormically, even after high-severity fire. Nevertheless, E. canobolensis response to repeat and short-interval fire remains unknown, and smaller trees appear to be vulnerable to top kill. Although much of Australia’s flora can respond to fire, this response is likely to be challenged as fire extents increase, especially if this is combined with increasing fire severity and/or frequency. These changes to the fire regime are a particular threat to species with restricted distributions.
... In such circumstances, trees regenerating after the first fire would not have yet produced meaningful quantities of viable seed before a second fire [117], and eucalypt regeneration would rely on seed dispersal from adjacent patches. Lack of tree regeneration after shortinterval fires in obligate seeder forests has been observed in the last decades with aerial sowing being required to address post-fire recovery in obligate seeder forests [118]. This highlights the impact that the observed changes in fire regimes have had on the resilience of eucalypt forests in south-eastern Australia [63,103]. ...
Wildfires have increased in size and frequency in recent decades in many biomes, but have they also become more severe? This question remains under-examined despite fire severity being a critical aspect of fire regimes that indicates fire impacts on ecosystem attributes and associated post-fire recovery. We conducted a retrospective analysis of wildfires larger than 1000 ha in south-eastern Australia to examine the extent and spatial pattern of high-severity burned areas between 1987 and 2017. High-severity maps were generated from Landsat remote sensing imagery. Total and proportional high-severity burned area increased through time. The number of high-severity patches per year remained unchanged but variability in patch size increased, and patches became more aggregated and more irregular in shape. Our results confirm that wildfires in southern Australia have become more severe. This shift in fire regime may have critical consequences for ecosystem dynamics, as fire-adapted temperate forests are more likely to be burned at high severities relative to historical ranges, a trend that seems set to continue under projections of a hotter, drier climate in south-eastern Australia.
... For example, Bowman et al. (2014) found that a single high severity fire in mature obligate seeder Eucalyptus delegatensis forests in Victoria reduced above ground carbon storage by 58% (from 404 Mg ha-1 to 169 Mg ha −1 ) with a second fire leading to 69% loss (124 Mg ha −1 ). A third fire was shown to have killed all the adult and juvenile trees that would have led to a loss of forest cover in the absence of directly sowing of seeds (Bassett, Prior, Slijkerman, Jamieson, & Bowman, 2015). More accurate assessments of post-fire carbon loss from Eucalyptus forests require field validated mapping of past logging and fire disturbances. ...
Over the Austral spring and summer of 2019/20 > 7 million ha of Eucalyptus forest and woodland, including some of Australia's most carbon dense ecosystems, were burnt on the east coast of Australia. We estimated bootstrapped mean CO2 emissions of c. 0.67 Pg, with other available estimates ranging from 0.55 to 0.85 Pg. Eucalyptus forests are renowned for their ability to resist and recover from wildfire so it would be expected that emitted CO2 will be reabsorbed. The combination of drought and frequent fires is likely reducing the capacity to recover from the fire so future Australian forests may store less carbon. Broadscale prescribed burning is a widely promoted approach to reduce uncontrolled wildfires, yet the benefits for the management of carbon stores are controversial. Prescribed burning can reduce carbon losses from subsequent wildfire, yet the “carbon costs” of it may equal or outweigh the “carbon benefits” in reduced wildfire emissions. Likewise, mechanical thinning of vegetation to reduce fuel loads also carries heavy carbon costs with uncertain carbon benefits. Research involving empirical measurements, modelling and a mix of large‐scale management intervention is urgently required to determine what interventions can maximise carbon storage in the face of climate change‐driven fires. In this Invited Review, we briefly describe the geographic scale of the 2019/20 Australian Black Summer Fires and undertake a quasi‐estimate of CO2 emissions from these fires. Although it is assumed the CO2 will be reabsorbed by post‐fire regrowth, we review evidence that this may not be the case because of climate change. We consider possible management interventions to reduce carbon losses from fires and reflect on the carbon costs and benefits of these management approaches. We conclude by highlighting the need for a much better understanding of fire‐driven carbon dynamics in Australian Eucalyptus forests to underpin future management.
... Reassessment of conservation status will be required to identify and list species that now face a palpable risk of extinction. Active restoration, including seed harvesting and aerial sowing of some forest ecosystems, will be needed if they are to persist following repeated recent fires [3]. There is a significant opportunity to couple postfire forest restoration efforts with carbon sequestrationfunding initiatives to leverage biodiversity conservation. ...
The 2019–2020 megafires in Australia brought a tragic loss of human life and the most dramatic loss of habitat for threatened species and devastation of ecological communities in postcolonial history. What must be done now to keep impacted species from extinction? What can be done to avoid a repeat of the impacts of such devastating bushfires? Here, we describe hard-won lessons that may also be of global relevance.
... However, communication between the ecology and remote sensing communities, on what can and should be measured from space, is lacking (Skidmore et al. 2015). Many studies exploring the ecological impacts of fire are conducted at a local scale, typically focussing on specific ecosystems, such as the mountain ash (Lindenmayer and Sato 2018) and alpine ash (Bassett et al. 2015) forests of south-east Australia. These studies contain highly detailed information over limited spatial extents. ...
Across the world, millions of hectares of forest are burned by wildfires each year. Satellite remote sensing, particularly when used in time series, can describe complex disturbance‐recovery processes, but is underutilized by ecologists. This study examines whether a greater disturbance magnitude equates to a longer recovery length, in the fire‐adapted forests of south‐east Australia. Using Landsat time series, spectral disturbance and recovery maps were first created, for 2.3 million hectares of forest, burned between 2002 and 2009. To construct these maps, a piecewise linear model was fitted to each pixel's Normalized Burn Ratio (NBR) temporal trajectory, and used to extract the disturbance magnitude (change in NBR) and the spectral recovery length (number of years for the NBR trajectory to return to its pre‐fire state). Pearson's correlations between disturbance magnitude and spectral recovery length were then calculated at a state level, bioregion level and patch level (600 m × 600 m, or 36 hectares). Our results showed overall correlation at the state level to be inconclusive, due to confounding factors. At the bioregion level, correlations were predominantly positive (i.e. a greater disturbance equals a longer recovery). At the patch level, both positive and negative correlations occurred, with clear evidence of spatial patterns. This suggests that the relationship between disturbance magnitude and recovery length is dependent on forest type. This was further explored by investigating the major vegetation divisions within one bioregion, which provided further evidence that relationships varied by vegetation type. In Heathy Dry Forests, for example, a greater disturbance magnitude usually led to a longer recovery length, while in Tall Mist Forests, the opposite behaviour was evident. Results of the patch‐level analysis were particularly promising, demonstrating the utility of satellite remote sensing in producing landscape scale information to inform policy and management. Satellite remote sensing, particularly when used in time series, can describe complex disturbance‐recovery processes, but is underutilized by ecologists. This study examines whether a greater disturbance magnitude equates to a longer recovery length, in the fire‐adapted forests of south‐east Australia. A novel patch‐based method is presented, which explores the relationships between spectral disturbance magnitude and recovery length. Spatial patterns are uncovered and are in turn linked to variations in forest types.
... In multiple burned sites, grasses and shrubs trees are rapidly displacing trees as the interval between fires is inadequate for seed production (of Alpine ash) or has diminished resprouting ability (for snow gum). This has led to drastic management interventions, such as aerial sowing programmes, to maintain Alpine ash ecosystems in burnt areas (Bassett et al. 2015). ...
The effects of anthropogenic climate change on biodiversity are well known for some high‐profile Australian marine systems, including coral bleaching and kelp forest devastation. Less well‐published are the impacts of climate change being observed in terrestrial ecosystems, although ecological models have predicted substantial changes are likely. Detecting and attributing terrestrial changes to anthropogenic factors is difficult due to the ecological importance of extreme conditions, the noisy nature of short‐term data collected with limited resources, and complexities introduced by biotic interactions. Here, we provide a suite of case studies that have considered possible impacts of anthropogenic climate change on Australian terrestrial systems. Our intention is to provide a diverse collection of stories illustrating how Australian flora and fauna are likely responding to direct and indirect effects of anthropogenic climate change. We aim to raise awareness rather than be comprehensive. We include case studies covering canopy dieback in forests, compositional shifts in vegetation, positive feedbacks between climate, vegetation and disturbance regimes, local extinctions in plants, size changes in birds, phenological shifts in reproduction and shifting biotic interactions that threaten communities and endangered species. Some of these changes are direct and clear cut, others are indirect and less clearly connected to climate change; however, all are important in providing insights into the future state of terrestrial ecosystems. We also highlight some of the management issues relevant to conserving terrestrial communities and ecosystems in the face of anthropogenic climate change.
... Yet, under high-severity fire regimes, stands of this species can be killed, leaving the sole regeneration strategy as a canopy seedbank that disperses with fire damage. Following stand-replacing fires, the immature cohort is vulnerable to fire kill due to both high stem density and high shrub cover [79], with multiple fires leading to local extinction [80]. Nonetheless, frequent fires can select for precocious flowering genotypes [81]. ...
The development of frameworks for better-understanding ecological syndromes and putative evolutionary strategies of plant adaptation to fire has recently received a flurry of attention, including a new model hypothesizing that plants have diverged into three different plant flammability strategies due to natural selection. We provide three case studies of pyromes/taxa (Pinus, the Proteaceae of the Cape Floristic Region, and Eucalyptus) that, contrary to model assumptions, reveal that plant species often exhibit traits of more than one of these flammability and post-fire recovery strategies. We propose that such multiple-strategy adaptations have been favoured as bet-hedging strategies in response to selective pressure from mixed-fire regimes experienced by these species over evolutionary time.
Athrotaxis cupressoides is an endemic conifer restricted to montane areas of Tasmania. It is slow‐growing and vulnerable to the increasing wildfire activity associated with climate change. We explored the novel idea that disused gravel pits could serve as artificial fire refugia for transplanted populations. We compared survival, growth, and response to fertilizer of nursery‐grown A. cupressoides transplants in these artificial refugia, which had mineral soils, and in burnt and unburnt sites in wilderness areas, which had organic soils. Survival over the 16‐month trial increased with initial transplant height and was slightly higher in the gravel pits (97%) than the wilderness areas (89%). Height growth of unfertilized plants was slow, especially in the unburnt wilderness sites and gravel pits. However, fertilizer boosted growth most strongly in the gravel pits, to rates similar to those of fertilized plants in unburnt wilderness sites. Our results show that it is feasible to reintroduce A. cupressoides into populations eliminated by wildfire. They also demonstrate the capacity to reclaim gravel pits by creating new localized populations of this iconic species. Thus, denuded gravel pits can be re‐imagined as fire refugia to help maintain populations of A. cupressoides and other long‐lived but fire‐sensitive plants in the wild.
Background
Changes to fire regimes threaten biodiversity worldwide and emphasize the need to understand the ecological consequences of fire management. For fire management to effectively protect biodiversity, it is essential to have ecologicallyrelevant metrics to plan and evaluate management interventions. Here, we describe a suite of metrics to guide fire management for enhanced biodiversity outcomes.
Results
We define five metrics that collectively provide comprehensive and complementary insights into the effect of fire regimes on ecosystem resilience and components of biodiversity. These include (1) Species Habitat Availability, a measure of the amount of suitable habitat for individual species; (2) Fire Indicator Species Index, population trends for species with clear fire responses; (3) Vegetation Resilience, a measure of plant maturity and the capability of vegetation communities to regenerate after fire; (4) Desirable Mix of Growth Stages, an indicator of the composition of post-fire age-classes across the landscape; and (5) Extent of High Severity Fire, a measure of the effect of severe fire on post-fire recovery of treed vegetation communities. Each metric can be quantified at multiple spatial and temporal scales relevant to evaluating fire management outcomes. We present a case study from Victoria, Australia, in which two metrics are applied across spatially-nested management areas. Results highlight four characteristics of metrics that enhance their value for management: (1) they quantify both status and trends through time; (2) they are scalable and can be applied consistently across management levels (from individual reserves to the whole state); (3) most can be mapped, essential for identifying where and when to implement fire management; and (4) their complementarity provides unique insights to guide fire management for ecological outcomes.
Conclusions
These metrics reflect common relationships between fire and biodiversity and are relevant to management in fire-prone ecosystems worldwide. They facilitate consistent translation of management responsibilities (planning, evaluation, reporting) across administrative levels and enable managers to strategically plan on-ground actions and transparently evaluate outcomes against strategic goals. A key next step for fire managers globally is to define “desirable” states for ecological metrics, to enable target-setting and the evaluation of management outcomes.
Forests constitute one of the most prominent bioresources on earth, having economic and ecological roles of unparalleled significance. Forests provide abundant natural resources and are major players in maintaining the environmental balance, providing numerous ecological services, and preserving biodiversity. Despite their great importance, the area under forests is constantly shrinking at an alarming rate due to both environmental conditions and anthropogenic activities. To add to the factors detrimental to forest health, climate change has emerged as a phenomenon perilous to the diversity of forest genetic resources. These contributing factors altogether call for immediate attention to the cause of forest germplasm collection and the implementation of conservation measures for the long-term storage of these precious forest resources. Many conservation strategies have been designed for the purpose of preserving germplasm from plant species. Among these, the manufacture and storage of synthetic seeds represent a promising approach. Synthetic seeds or synseeds are developed by encapsulation of explants (meristems or embryos) in a nutritive alginate matrix that serves to help in regrowth when required. Synthetic seed technology has several potential applications in forest tree species. It can be utilized for the rapid reproduction of elite genotypes, conservation of threatened species, generation of disease-free planting stock, and germplasm storage for longer periods of time, and at the same time, it can potentially reduce labor, monetary expenses, and space requirements for propagation. To date, this technique has been used for a wide number of tree species of the forests, including conifers such as pine, spruce, and fir, and broad-leaved species, such as eucalypts, acacias, oak, willow, and Shisham. The present chapter attempts to collate available knowledge on the synthetic seed technology and how they are produced and the propagules used therein, with an emphasis on its application in the forestry sector. The future of synthetic seed technology seems bright as it may be utilized as an effective method for mass propagation and the preservation of forest tree biodiversity, especially rare species, for short- and long-term.
Our Changing Snowscapes reviews the current state of climate change impacts on the Australian Alps and puts forward recommendations for a better path forward.
This report summarises a broad expanse of literature about current and projected climate change impacts on the Australian Alps and presents new Australia-first modelling of climate change impacts on the Australian ski industry. The report highlights a cascading series of interconnected impacts across alpine tourism, regional communities, hydroelectricity, high country water flows to the Murray-Darling Basin, carbon sequestration, high country ecosystems, and First Nations impacts and makes recommendations on how best to respond to these impacts.
The spectacular Australian Alps extend over 1.6 million hectares of public land contained in 11 national parks and nature reserves across New South Wales (NSW), Victoria (VIC), and the Australian Capital Territory (ACT). They are home to nationally significant winter-tourism sectors, thriving and passionate regional communities and some of Australia's most unique and fragile landscapes.
The impact of climate change on temperature, precipitation, and snow conditions in the Australian Alps is stark and has been heralded for more than three decades. In 1988, it was predicted that climate change will drastically impact the Australian Alps, and that even small temperature increases would have a catastrophic impact on the Australian winter tourism industry. The Australian snowpack is now at a 2,000-year low. Snow cover between 1954 and 2012 has reduced by 30% and the length of the ski season has already contracted by 17% - 28% across most Australian alpine resorts. Businesses and regional communities at present are experiencing the impacts of climate change and these impacts are projected to worsen rapidly without decisive climate mitigation.
Changes to the spatiotemporal patterns of wildfire are having profound implications for ecosystems and society globally, but we have limited understanding of the extent to which fire regimes will reorganize in a warming world. While predicting regime shifts remains challenging because of complex climate–vegetation–fire feedbacks, understanding the climate niches of fire regimes provides a simple way to identify locations most at risk of regime change. Using globally available satellite datasets, we constructed 14 metrics describing the spatiotemporal dimensions of fire and then delineated Australia's pyroregions—the geographic area encapsulating a broad fire regime. Cluster analysis revealed 18 pyroregions, notably including the (1) high‐intensity, infrequent fires of the temperate forests, (2) high‐frequency, smaller fires of the tropical savanna, and (3) low‐intensity, diurnal, human‐engineered fires of the agricultural zones. To inform the risk of regime shifts, we identified locations where the climate under three CMIP6 scenarios is projected to shift (i) beyond each pyroregion's historical climate niche, and (ii) into climate space that is novel to the Australian continent. Under middle‐of‐the‐road climate projections (SSP2‐4.5), an average of 65% of the extent of the pyroregions occurred beyond their historical climate niches by 2081–2100. Further, 52% of pyroregion extents, on average, were projected to occur in climate space without present‐day analogues on the Australian continent, implying high risk of shifting to states that also lack present‐day counterparts. Pyroregions in tropical and hot‐arid climates were most at risk of shifting into both locally and continentally novel climate space because (i) their niches are narrower than southern temperate pyroregions, and (ii) their already‐hot climates lead to earlier departure from present‐day climate space. Such a shift implies widespread risk of regime shifts and the emergence of no‐analogue fire regimes. Our approach can be applied to other regions to assess vulnerability to rapid fire regime change.
Aerial seeding popularly known as "seed bombing" is an innovative approach to ecological restoration which has emerged as a game-changing tactic for overcoming the difficulties associated with large-scale vegetation recovery in a variety of landscapes. In order to achieve a thorough analysis, the methodology, ecological effects, and potential to support long-term habitat restoration is the need of the era. Seed bombs provides protection by encapsulating the seeds with suitable substrates creating a congenial microenvironment improving viability, vigor and germination. They can rapidly span extensive landscapes, even in remote and challenging terrains, enhancing the probability of successful revitalization and restoring crucial habitats through the deliberate selection of appropriate plant species. Therefore, improvements in aerial delivery technologies, such as the use of drones and specialized aircraft offer control and precision in seed dispersal, ensuring ideal seed distribution patterns and maximizing ecosystem recovery.
Under the current trajectory of accelerated climatic and environmental change, many forests are at risk of regeneration failure and subsequent transition to alternate stable states including non-forests or grassland. These regimes shifts can have severe ecological impacts and compromise carbon stores, undermine climate change mitigation, and create conditions incompatible with the survival of biodiversity. However, detailed empirical-based understanding of the alternative states associated with disturbance regime shifts is limited. Here, using a manipulative experiment, and controlling for seed application, we document temporal patterns of vegetation structure and composition associated with regeneration failure after clearcut logging in the ash-type eucalypt forests in south-eastern Australia. Our findings clearly demonstrate that in the absence of direct seed input, frequent stand-replacing disturbance can result in regeneration failure in these forests leading to them being replaced by low species diversity Acacia woodland. These insights can be extrapolated to scenarios of post-fire regeneration failure, where frequent fire precludes the development of adequate seed-stores (<21 years). Such shifts to alternative stable states can have severe ecological implications which require management intervention to circumvent and conserve the functional integrity of these forests. Our case study demonstrates the value of manipulative empirical experiments in quantifying the potential aftermath of forest regeneration failure. Such experiments may be useful to support theories and models in quantifying the ecological implications of regeneration failure, and to guide the application of management interventions for restoration where empirical-based knowledge of these states is limited.
Context
Increases in fire frequency, intensity and extent are occurring globally. Relative to historical, Indigenous managed conditions, contemporary landscapes are often characterised by younger age classes of vegetation and a much smaller representation of long-unburnt habitat.
Objectives
We argue that, to conserve many threatened vertebrate species in Australia, landscape management should emphasise the protection of existing long-unburnt patches from fire, as well as facilitate the recruitment of additional long-unburnt habitat, while maintaining historically relevant age distributions of more recently burned patches.
Methods
We use a range of case studies and ecosystem types to illustrate three lines of evidence: (1) that many threatened vertebrate species depend on mid- to late-successional ecosystem attributes; (2) disturbance to long-unburnt habitat tends to increase risk of future disturbance and ecosystem collapse; and (3) contemporary landscapes exhibit a range of characteristics that differ to historical conditions and require context-specific management.
Conclusions
It is crucial that we adequately consider the implications of altered contemporary landscapes for management activities that aim to conserve threatened vertebrates. Contemporary landscapes often lack a range of critical structural and compositional components typical of late-successional habitat that are required for the persistence of threatened vertebrates. We need to shift towards strategic, objective-driven approaches that identify and protect long-unburnt habitats and promote their recruitment to enable recovery of many declining and threatened species.
The vulnerability to repeated high severity fires of tall wet eucalypt forests (TWEF) dominated by obligate seeder species is widely understood. However, 80% of Tasmania’s TWEF are dominated by resprouter species, and while these forests are more resilient to wildfire than those dominated by obligate seeders, the degree of their resilience is not well documented. Recently, two wildfires affected five 1-ha forest plots that had been previously measured, providing the opportunity to assess fire effects on these forest stands. We characterised these wildfires using remote sensing and field measurements of char height (a proxy for fire intensity) and canopy scorch (fire severity). We assessed the influence of tree diameter, fire intensity and seedling densities on the survival and resprouting responses of eucalypt overstorey trees and mixed species understorey trees. Our results showed that these fires were predominantly of low to moderate intensity and severity. Our results showed that mature TWEF were resilient to these wildfires, with overall eucalypt survival of 75%. The major eucalypt species were either mostly not defoliated (E. regnans), or could recover rapidly by epicormic resprouting (E. delegatensis and E. obliqua). Results from this and other studies show recovery from topkill caused by high severity fires occurs but is slower, by basal resprouting (E. obliqua) or from seed (all species). By contrast, understorey species suffered high mortality (85% overall), with few species showing substantial resprouting. Fire resistance in both groups increased markedly with tree diameter.
Our results have implications for forest management. The high survival of overstorey eucalypts leads to a multi-aged stand structure in most unlogged old growth TWEF in Tasmania. On the other hand, clearfell logging, originally designed to mimic stand replacing wildfire in obligate seeder systems, creates a vulnerable, even aged stand of young regrowth, and at a landscape scale, it also reduces average tree size, reducing overall resistance to fire. Adopting alternatives to clearfelling, such as partial logging systems, will increase landscape resilience to fire, as well as providing other previously shown benefits.
Forest fire risk, and how it changes over time, has important influences on forest dynamics. Two common models describing how fire risk changes with stand development, known as flammability functions, are (a) the ‘moisture model’, where fire risk initially increases, then decreases, as a stand develops after a fire, and (b) the ‘Olson model’, where fire risk increases asymptotically as a function of time since previous fire. These two flammability functions have both been used to describe the world’s tallest angiosperm forest, the Australian tall wet Eucalyptus forest (TWEF). It is unclear, however, which function is more appropriate for TWEF, as there are little empirical data describing fuels and microclimate, two important influences on fire risk and potential severity, across the long lifespan of these forests. Accordingly, we use a chronosequence of TWEF stands in southeast Tasmania, Australia, to see how fuels, microclimate, and resulting fire risk and potential fire severity changed amongst four stand-development stages ranging from regrowth to old forests. We measured fuel loads, understorey microclimate, and forest physiognomy. We then used these data with historical fire weather data and fire behaviour models to estimate how often low- and high-severity fire was possible historically. We also investigated if the severity of the previous disturbance influenced the likelihood of a subsequent high-severity fire. We found that, while fuel loads remained unchanged across the chronosequence, later development stages had a significantly moister understorey, an increased abundance of rainforest trees, and more vertically discontinuous fuels. These factors resulted in a significantly reduced fire risk, with high-severity fire much more likely in the early stages. Further, we found that stands that had been initiated by stand-replacing fire were more susceptible to subsequent high-severity fire than those that experienced non stand-replacing fire, due to a lack of a remaining mature canopy. We concluded that, unlike most other fire-dependent ecosystems where the Olson curve is an appropriate model, the flammability function in TWEF is best described by the moisture model. Our results indicate that TWEF is vulnerable to a ‘landscape trap’ effect, where intensive disturbance creates large areas of regrowth stands with increased risk of high-severity fire, which increases the likelihood of landscape-wide, demographic collapse. We suggest that fire and forest management incorporate techniques mimicking low-severity disturbances to create more resilient landscapes.
In recent years, novel, high-severity wildfire regimes have driven major changes in the structure and function of forests globally. Indeed, many forests are vulnerable to recruitment failures and collapse in the event of decreased intervals between fires, including forests dominated by the Australian obligate seeders, Alpine Ash (Eucalyptus delegatensis) and Mountain Ash (Eucalyptus regnans). Disturbance responses in these forests are often described collectively, with limited understanding of their potential differences. Despite this, management recommendations and ecological implications are often applied broadly across both forest types. Here, using an empirical dataset collected over an eleven-year period (2009–2020), we compare plant communities in south-eastern Australian Alpine Ash and Mountain Ash forests in mature stands (last burned in 1926/1939), and young stands (burned by high-severity wildfire in 2009). To do this, we used measures of forest structure (basal area of dominant plant life-forms) collected over eight years, and the abundance (projective foliage cover) of vascular plant species. We provide evidence of similar, positive-linear trends in the recovery of forest structure in both Alpine Ash and Mountain Ash forests in the first eight years post-wildfire in 2009. Mature Alpine Ash and Mountain Ash forests were compositionally different but had a similar structure and abundance of plant life-forms. Moreover, controlling for the influence of forest type, young stands were compositionally different from mature stands, and were associated with an increase in the abundance of Acacia, herb, ground-fern and graminoid species, and a decline in tree-fern and tree species. Further investigation in young stands revealed marked differences in plant community composition between forest types, with young Mountain Ash forests characterized by a lower abundance of shrub, Acacia and graminoid species, relative to Alpine Ash forests of the same age. Overall, our findings indicate that Alpine Ash and Mountain Ash forest plant communities may have similar structural and functional responses to predicted increases in wildfire. This suggests that when the broad structure and function of forest vegetation is a consideration, ecological implications and management recommendations may be broadly applicable to both Alpine Ash and Mountain Ash forests. However, further consideration is required in early successional stands where differences in species composition between forest types may have implications for management (e.g. increases in flammability). In a period of uncertainty in the future of ash-type forests, our study provides a timely insight into the comparative successional trajectories of their respective plant communities and provides a baseline for future studies.
Increased fire frequency can result in a decline of obligate seeding plants, which rely on re‐seeding for population persistence following canopy scorching fire. The resilience of obligate seeding plants to fire at any point in time depends on plant maturity and the size of plants in relation to potential fire scorch height. We investigated variation in the resilience of post‐fire regenerating Eucalyptus delegatensis subsp. delegatensis (alpine ash) to a short inter‐fire interval at its boundaries with E. fastigata (brown barrel) stands. The resilience of post‐fire E. delegatensis regeneration was modelled across these stand boundaries as a function of the height of the plants, their reproductive maturity and predicted fire behaviour derived from local fuel characteristics. We measured these attributes 14 years following the Canberra 2003 wildfires and stratified study sites by fire severity. The height and reproductive maturity of post‐fire E. delegatensis saplings decreased at stand boundaries with E. fastigata, while fuel was uniformly abundant and capable of supporting canopy scorching fire under mild fire weather conditions. This suggests that E. delegatensis is less resilient to frequent fire in the presence of interspecific competition and other environmental conditions that occur at stand boundaries, which represent the edge of the species’ realised niche. With forecasts for increased fire frequency in south eastern Australia, persistence of E. delegatensis may be greatest in pure stands corresponding to the core of the species’ realised niche, and in moist and sheltered topographic areas that are less prone to frequent canopy scorching fire. Our findings suggest the importance of considering fine‐scale spatial variation in important obligate seeding plant traits when predicting and managing the response of obligate seeding species to frequent fire.
Disturbance plays an important role in determining whether forests are carbon sinks or sources. Logging and wildfire are common widespread disturbances known to significantly reduce carbon stocks in carbon rich forests, such as, the tall forests of south-eastern Australia. Most tall forests in south-eastern Australia are dominated by globally unique resprouting Eucalypts that experience limited mortality after high severity wildfire. However, the most carbon dense forests in the region are dominated by non-resprouting Eucalypts that, like many other species associated with carbon dense forests around the world, experience stand replacement after high severity wildfire. We used space-for-time surveys to measure how above ground carbon stocks change with time since logging and time since wildfire in resprouting and non-resprouting Eucalypt forests in south-eastern Australia. Logging reduced above ground carbon stocks much more than wildfire in both forest types. Carbon stock losses caused by wildfire were more substantial in non-resprouting forests than resprouting forests, which experience only minor losses after wildfire. The recovery of carbon stocks after wildfire began to asymptote after approximately 40 years but increased almost continuously with time since logging in both forest types. Carbon stock losses associated with logging represent a much greater departure from natural disturbance in resprouting forests, because wildfire causes relatively little carbon loss in resprouting forests compared to non-resprouting forests. This analysis highlights the need to consider specific biological responses when assessing forest carbon stock losses associated with disturbance. Consideration of these dynamics is essential in addressing carbon stock risk mitigation.
Fire's growing impacts on ecosystems
Fire has played a prominent role in the evolution of biodiversity and is a natural factor shaping many ecological communities. However, the incidence of fire has been exacerbated by human activity, and this is now affecting ecosystems and habitats that have never been fire prone or fire adapted. Kelly et al. review how such changes are already threatening species with extinction and transforming terrestrial ecosystems and discuss the trends causing changes in fire regimes. They also consider actions that could be taken by conservationists and policy-makers to help sustain biodiversity in a time of changing fire activity.
Science , this issue p. eabb0355
Eucalyptus delegatensis is native to the Australian Alps (subsp. delegatensis) and montane Tasmania (subsp. tasmaniensis). Post-fire regeneration mechanisms of the obligate-seeder subspecies on the Australian mainland are well-known, but less is known about the resprouter Tasmanian subspecies. In January 2016, large tracts of Eucalyptus delegatensis forests in central Tasmania, logged at different intensities, were burnt by low- and high-severity fire. We used statistical modelling to understand how tree survival, vegetative regeneration and seedling recruitment differed according to understorey type, fire severity, logging intensity and tree size (DBH). Fire severity, defined as unburnt, low-severity (fire scarring on the stem and/or lower canopy burnt) and high-severity (full canopy burnt), affected tree survival: 84% of trees were alive in unburnt transects, compared with 43% in low-severity transects and 36% in high-severity transects. Epicormic resprouting was the dominant mode of vegetative recovery, with < 1% of total trees recovering solely by basal resprouting. Fire severity significantly affected epicormic resprouting, with 70% of live stems resprouting post-fire in low-severity transects and 99% in high-severity transects, compared with 4% in unburnt transects. Tree survival was strongly influenced by tree size: in high-severity transects, 24% of trees with DBH < 20 cm were alive, compared with 88% of trees with DBH ≥ 20 cm. These differences in survival were primarily because large trees were more likely to resprout epicormically, with epicormic shoots present on 24% of live trees with DBH < 20 cm, compared with 79% of live trees with DBH ≥ 80 cm. The strong effect of tree size renders clear-felled forests especially vulnerable to fire during the several decades when all the regenerating trees are small (DBH < 20 cm). Seedling recruitment was uncommon, independent of understorey type and logging intensity, but with higher occurrence on high-severity (54%) than low-severity (19%) or unburnt (15%) transects. When present, seedling densities were typically low: median = 400 and maximum = 4·10⁴ seedlings ha⁻¹. This study highlights that mature forests of Eucalyptus delegatensis in Tasmania are more resilient (able to return to pre-disturbance conditions) to single high-severity fires than their mainland counterparts, because they can recover more quickly through epicormic resprouting. However, clear-felling reduces this resilience for several decades because it decreases median tree size and, hence, leads to higher post-fire mortality. It is difficult to predict how the Tasmanian subspecies will respond to an increased frequency of high-severity fires associated with a projected warmer and drier climate.
This Occasional Paper is the result of a large collaborative effort by fire scientists and practitioners who believe that learning to co-exist with changing fire activity is not only possible but necessary if we, as a global society, are to adapt to climate change and keep our natural and cultural landscapes healthy, resilient, and safe for the next generations. The work presented hereafter was developed during, and as follow-up to, the Global Expert Workshop on Fire and Climate Change hosted in Vienna, Austria, in July 2018. It stresses the diversity and the complexity of the global fire situation, a situation that is evolving, positively or negatively, in unknown proportions due to global environmental changes — with climate change being the most acknowledged manifestation.
Aspects of the scientific discipline of forestry have endured decades of environmental activism aimed at discrediting it. Much of this activism has entailed strategic avoidance of inconvenient truths while promoting myths, half-truths and pseudo-science as though they are absolute fact. However, arguably of greater concern are more recent instances of false or unsupported claims about native forest management contained in some conservation-focussed research published in peer-reviewed scientific journals.
This paper examines recent scientific literature which addresses Leadbeater’s possum and broader conservation issues in the forests of Victoria’s Central Highlands. In assessing its contribution to the public and political discourse on forest management we identified the following six areas where much of this research is contentious:
• Leadbeater’s possum population estimates
• The proportions of forests respectively catering for conservation or wood production
• Value of active forest management strategies for conserving Leadbeater’s possum
• Forest carbon stocks
• The concept of ecosystem collapse
• Value of environmental services derived from native forests.
This contentious research is characterised by the omission of critically important context, reliance on flawed or wrong assumptions and errant citation practices. In the past, there would have been an expectation of such problems being identified and excluded during effective peer review by appropriate scientists. That this is no longer guaranteed is indicative of broken academic protocols.
We conclude that there is evidence of a disturbing synergy between some peer-reviewed science and environmental activism in fashioning and promoting a questionable case for forest management change—in this instance, through advocacy of a proposed new national park that would restrict or end a range of public activities and decimate a significant and sustainable local timber industry.
Eucalypts encounter a wide range of severe disturbances such as extensive defoliation by insects, major structural damage from cyclonic winds, as well as foliage and bark loss during drought and fire. Most healthy, mature eucalypts are not killed by these events, but regenerate vegetatively. With increasing intensity of disturbance, resprouting first occurs from the accessory buds in the small-diameter branchlets of the crown, followed by the epicormic buds in the medium- and large-diameter branches and stems, and then from the buds of the lignotuber. All these modes of regeneration are ultimately dependent on preventitious buds and, thus, the present review concentrates on axillary buds, their subsequent development into epicormic or lignotuber buds and their degree of protection from fire. The eucalypts have remarkably abundant, well protected and anatomically distinctive bud-forming structures in their leaf axils, branches, stems and lignotubers. These structures are quite consistent across this large genus, but are generally different from resprouting structures in many other plants. From an anatomical perspective, these structures seem best adapted to regeneration after fire, rather than damage from insects, storms or drought and this also correlates with ecological observations. On a worldwide basis, the eucalypts are some of the most successful post-fire resprouters, especially epicormic resprouting after medium- and high-intensity fires. Given the apparent ecological advantages of epicormic resprouting (the rapid reestablishment of extensive leaf area while simultaneously shading basal resprouters and seedlings) this could be an important factor in the success of eucalypts in Australia. Recent phylogenetic analysis has indicated a long relationship between eucalypts, fire and bud structures that facilitate resprouting.
This study describes changes in the abundance of shrub species after two fires in 1979 and 1980 on Otay Mountain in San Diego County, California. The 1979 fire burned a large area of dense chaparral and coastal sage scrub. The 1980 fire burned a portion of the 1979 fire area that had been seeded with annual ryegrass (Lolium multiflorum) as an erosion protection measure. Changes in the vegetation caused by the 1979 fire alone were similar to those commonly seen in chaparral wildfire, but the reburning of the vegetation in 1980 caused drastic changes in some areas. Ceanothus oliganthus was almost completely eliminated from the area of the 1980 burn. Adenostoma fasciculatum, the most abundant shrub at the study site, was reduced in density by up to 97%. Even Xylococcus bicolor, which normally resprouts with complete success after fire, suffered substantial mortality with reburning. It is concluded that the changes brought about by the 1980 fire will certainly persist for many decades. While sudden shifts in vegetation composition probably occurred without human intervention, we believe that human activity, especially after the introduction of aggressive annual grasses 200 yr ago, has caused an increase in the instances of abrupt change.
Climatic change is anticipated to alter disturbance regimes for many ecosystems. Among the most important effects are changes in the frequency, size, and intensity of wildfires. Serotiny (long-term canopy storage and the heat-induced release of seeds) is a fire-resilience mechanism found in many globally important terrestrial ecosystems. Life-history traits and physiographic differences in ecosystems lead to variation in serotiny; therefore, some systems may exhibit greater resilience to shifting disturbances than others do. We present a conceptual framework to explore the consequences of changing disturbance regimes (such as mean and variance in fire severity or return intervals) to serotinous species and ecosystems and implications of altered serotinous resilience at local and regional scales. Four case studies are presented, and areas needing further research are highlighted. These studies illustrate that, despite the reputed fire resilience of serotiny, more fire does not necessarily mean more serotinous species across all systems in which they occur.
A regeneration predictor (RP) has been elaborated to forecast the minimal
inter-fire period, required for full recovery (assumed at 1,000 mature stems ha-1, a typical
value for a dense pine forest) of an even-aged, postfire regenerating Pinus halepensis
population after a subsequent wildfire, in the future. The study has been conducted in three
Aleppo pine forests of northern Euboea Island, Greece. Postfire field surveys of sapling
growth, sapling density and reproductive dynamics (cone-bearing population fraction,
annual cone and seed production per sapling, canopy seed bank build-up) were carried out
for three, consecutive growing seasons (years). Additional postfire parameters, with values
estimated from literature data, have been also included in order to devise the RP. In the
cases of the three populations studied, the application of this RP provides time-windows
for full recovery after a recurrent fire, as short as 10–15, 8–11 and 7–11 years, respectively
(values corresponding to best and worst scenarios). It is suggested that in even-aged,
postfire regenerating Aleppo pine populations, the minimal inter-fire period required for
full recovery can be predicted by monitoring a few selected variables, namely (a) sapling
density, (b) vegetative to reproductive shift dynamics, and (c) cones/sapling and germinable
seeds/cone, for at least 2 years (either consecutive or 2–3 years apart) at a postfire age
of 7–12 years.
With projected climate change, we expect to face much more forest fire in the coming decades. Policymakers are challenged not to categorize all fires as destructive to ecosystems simply because they have long flame lengths and kill most of the trees within the fire boundary. Ecological context matters: In some ecosystems, high-severity regimes are appropriate, but climate change may modify these fire regimes and ecosystems as well. Some undesirable impacts may be avoided or reduced through global strategies, as well as distinct strategies based on a forest’s historical fire regime.
Large fires can have marked impacts on forest ecology and consequently on hydrology, including catchment water yields. Decisions on levels of fire protection and post-fire forest management require accurate information on the consequences of fire, including forest hydrological responses. In February 2009, wildfires burnt large areas of wet sclerophyll eucalypt forest in catchments supplying water to the city of Melbourne, Australia. Fire intensity was highly spatially variable, ranging from low intensity surface fire to high intensity crown fire. A survey of forest survival in three catchments 10–15 months after the fires revealed a good correspondence between overstorey survival and a satellite-based fire severity rating.
This study investigated the economics of maintaining strategic seedbanks for key eucalypt species to facilitate forest recovery following major fires in fire-sensitive forests of mountain ash (Eucalyptus regnans) and alpine ash (E. delegatensis) in Victoria. The analysis was confined to state forests and used Monte Carlo processes to model the occurrence of good seed-production years, the extent of natural regeneration occurring after major fires, the occurrence of minor and major fires, and the areal extent of those fires. The occurrence of major fires was predicted from estimates of the mean intervals between fires and long-term trends were also superimposed on these values to take account of future climate change. Three alternative scenarios for the extent of seed collection in good seed production years were investigated, together with three alternative strategies for future seed collection and storage facilities. The choice between these strategies and scenarios was evaluated using a discounted net cost criterion, together with consideration of the tradeoffs with risks associated with (1) backlogs of regeneration, (2) biological viability and (3) timber production of each forest type. The results provided clear guidance as to seed collection and storage facilities and to the initial targets for seed collection in good seed-production years. The results for risks raise a number of concerns about the future of these forest types, especially for alpine ash, given the distribution of age classes following major fires in 2003, 2006–2007 and 2009. Beyond 2050, even the high levels of seed collection and storage recommended may not be sufficient to maintain these ash forest types within state forests, which are extremely important for water production, water quality, biodiversity and timber production, and consideration needs to be given to additional measures and research.
Increasing fire recurrence is a major problem threatening Mediterranean-type ecosystems. Moreover, this pattern is predicted to increase owing to global change. Although a reduction in the density and growth of post-fire regeneration is usually observed in recurrently burnt areas, the potential effects on reproductive ability have seldom been explored. The aim of the present study is to investigate whether structural changes induced by fire recurrence may constrain reproduction ability of Pinus halepensis forests. We conducted the current study in Catalonia (NE Spain) in 12 study sites, consisting of two adjacent areas differing in the number of fire events suffered throughout the last 16 years (one v. two fires). Twice-burnt areas showed a lower density of pines, lower pine height and a lower reproductive ability, namely (i) a 3-year delay in the onset of pine reproduction; (ii) a reduction of 52% in the number of reproductive pines; and (iii) a 36% lower mean cone crop per tree. The lower mean cone production per tree coupled with a lower density resulted in an ~80% lower canopy seed bank in twice-burnt areas. These results suggest that the occurrence of a third fire event in twice-burnt areas would severely constrain natural regeneration.
Post-fire regeneration of Pinus halepensis, the most abundant tree in the Mediterranean Basin, can vary largely. In the present work, we aim to study the parameters determining this variability in the eastern Iberian Peninsula. For this reason we sampled in 2002 the sapling pine density on 22 plots that burned in 1993 and 71 plots that burned in 1994. Pre-fire vegetation (tree density and basal area) were obtained from the Spanish Forest Inventory. The regeneration ranged from 0.006 to 20.4pines/m2 (mean=1.24, S.D.=3.22). The statistical analysis suggested that the most important variables explaining this variability were the amount of branches found on the forest floor (branches collapsed from burned trees or branches left by foresters), the aspect of the plot, the pre-fire basal area, and whether the slope was terraced or not. High regeneration was observed in forests with large amounts of branches on the floor (which create appropriate microclimatic conditions), with northern aspects, with high pre-fire basal area, and on terraced slopes. Furthermore, other water-related variables (annual precipitation and slope) also had some (although lower) importance. These results have direct implications for forest managers in the study area.
Assisted colonisation has received considerable attention recently, and the risks and benefits of introducing taxa to sites beyond their historical range have been vigorously debated. The debate has primarily focused on using assisted colonization to enhance the persistence of taxa that would otherwise be stranded in unsuitable habitat as a consequence of anthropogenic climate change and habitat fragmentation. However, a complementary motivation for assisted colonisation could be to relocate taxa to restore declining ecosystem processes that support biodiversity in recipient sites. We compare the benefits and risks of species introductions motivated by either goal, which we respectively term ‘push’ versus ‘pull’ strategies for introductions to preserve single species or for restoration of ecological processes. We highlight that, by focusing on push and neglecting pull options, ecologists have greatly under-estimated potential benefits and risks that may result from assisted colonisation. Assisted colonisation may receive higher priority in climate change adaptation strategies if relocated taxa perform valuable ecological functions (pull) rather than have little collateral benefit (push). Potential roles include enhancing resistance to invasion by undesired species, supporting co-dependent species, performing keystone functions, providing temporally critical resources, replacing taxa of low ecological redundancy, and avoiding time lags in the provisioning of desired functions.
During June 1998, a severe windstorm caused significant damage to a sub-alpine stand of Eucalyptus delegatensis (Myrtaceae) at the Snowy River National Park. In 2002, about 4.5 y after the windstorm, a study documented the effects on E. delegatensis and early understorey succession. In February 2003, wildfire burnt across the windthrow site and we examined the seedling recruitment patterns at windthrow-burn and burn-only sites. Our aim was to document the regeneration of the canopy-dominant E. delegatensis and to confirm that Acacia dealbata is a pioneer species that potentially interferes with or prevents regeneration of E. delegatensis. Permanent transects were established within the windthrow-burn and burn-only sites. The data suggest that the heavily disturbed (mounded) soil at the windthrow site had a strong positive influence on regeneration of both species. By providing favourable growing conditions, the disturbed soil appears to have assisted seedling survival and subsequent growth of the E. delegatensis, despite competition from dense, concurrently established A. dealbata.
Many criteria for statistical parameter estimation, such as maximum likelihood, are formulated as a nonlinear optimization problem. Automatic Differentiation Model Builder (ADMB) is a programming framework based on automatic differentiation, aimed at highly nonlinear models with a large number of parameters. The benefits of using AD are computational efficiency and high numerical accuracy, both crucial in many practical problems. We describe the basic components and the underlying philosophy of ADMB, with an emphasis on functionality found in no other statistical software. One example of such a feature is the generic implementation of Laplace approximation of high-dimensional integrals for use in latent variable models. We also review the literature in which ADMB has been used, and discuss future development of ADMB as an open source project. Overall, the main advantages of ADMB are flexibility, speed, precision, stability and built-in methods to quantify uncertainty.
CONTENTS: Summary 1 I. Introduction 1 II. Giant eucalypts in a global context 2 III. Giant eucalypts - taxonomy and distribution 4 IV. Growth of giant eucalypts 6 V. Fire and regeneration of giant eucalypts 8 VI. Are giant eucalypts different from other rain-forest trees? 9 VII. Conclusions 10 Acknowledgements 11 References 11 SUMMARY: Tree species exceeding 70 m in height are rare globally. Giant gymnosperms are concentrated near the Pacific coast of the USA, while the tallest angiosperms are eucalypts (Eucalyptus spp.) in southern and eastern Australia. Giant eucalypts co-occur with rain-forest trees in eastern Australia, creating unique vegetation communities comprising fire-dependent trees above fire-intolerant rain-forest. However, giant eucalypts can also tower over shrubby understoreys (e.g. in Western Australia). The local abundance of giant eucalypts is controlled by interactions between fire activity and landscape setting. Giant eucalypts have features that increase flammability (e.g. oil-rich foliage and open crowns) relative to other rain-forest trees but it is debatable if these features are adaptations. Probable drivers of eucalypt gigantism are intense intra-specific competition following severe fires, and inter-specific competition among adult trees. However, we suggest that this was made possible by a general capacity of eucalypts for 'hyper-emergence'. We argue that, because giant eucalypts occur in rain-forest climates and share traits with rain-forest pioneers, they should be regarded as long-lived rain-forest pioneers, albeit with a particular dependence on fire for regeneration. These unique ecosystems are of high conservation value, following substantial clearing and logging over 150 yr.
Several recent papers have suggested replacing the terminology of fire intensity and fire severity. Part of the problem with fire intensity is that it is sometimes used incorrectly to describe fire effects, when in fact it is justifiably restricted to measures of energy output. Increasingly, the term has created confusion because some authors have restricted its usage to a single measure of energy output referred to as fireline intensity. This metric is most useful in understanding fire behavior in forests, but is too narrow to fully capture the multitude of ways fire energy affects ecosystems. Fire intensity represents the energy released during various phases of a fire, and different metrics such as reaction intensity, fireline intensity, temperature, heating duration and radiant energy are useful for different purposes. Fire severity, and the related term burn severity, have created considerable confusion because of recent changes in their usage. Some authors have justified this by contending that fire severity is defined broadly as ecosystem impacts from fire and thus is open to individual interpretation. However, empirical studies have defined fire severity operationally as the loss of or change in organic matter aboveground and belowground, although the precise metric varies with management needs. Confusion arises because fire or burn severity is sometimes defined so that it also includes ecosystem responses. Ecosystem responses include soil erosion, vegetation regeneration, restoration of community structure, faunal recolonization, and a plethora of related response variables. Although some ecosystem responses are correlated with measures of fire or burn severity, many important ecosystem processes have either not been demonstrated to be predicted by severity indices or have been shown in some vegetation types to be unrelated to severity. This is a critical issue because fire or burn severity are readily measurable parameters, both on the ground and with remote sensing, yet ecosystem responses are of most interest to resource managers.
The life history of Spanish pines and their relation to fire as the main disturbance factor in their ecosystems was analysed.
The primary ecological attributes studied were the canopy seed bank (onset of cone production, percentage and persistence
of serotinous cones), seed and cone morphology, sprouting and bark thickness. Four ecological groups were separated using
multivariate cluster analysis and their life-history characteristics are discussed. Serotiny and early flowering in Pinus halepensis and P. pinaster reflect their evader strategy in relation to fire as this character is advantageous to survive frequent crown fires and to
attain successful post-fire recruitment. Late flowering and absence of serotinous cones in P. nigra, P. sylvestris and P. uncinata indicate that their natural forest did not evolve under frequent crown fires. P. canariensis and P. pinea appeared in two single groups because of their sprouting capability and their seed size respectively. Intraspecific variation
in P. pinaster was also analysed using the same criteria and high variability was found in its life history traits. A group of P. pinaster populations showed high levels of serotiny and thin bark as a possible adaptation to frequent stand-replacing crown fires.
In contrast, a group of non- or weakly-serotinous populations seems to have evolved under a low-intensity fire regime where
the best fitness corresponds to thick-barked individuals capable of surviving ground fires. Intermediate strategies were also
evident in this species and were discussed in relation to the effect of different fire regimes caused by the understorey vegetation.
Ecosystem patterns and disturbance processes at one spatial scale often interact with processes at another scale, and the
result of such cross-scale interactions can be nonlinear dynamics with thresholds. Examples of cross-scale pattern-process
relationships and interactions among forest dieback, fire, and erosion are illustrated from northern New Mexico (USA) landscapes,
where long-term studies have recently documented all of these disturbance processes. For example, environmental stress, operating
on individual trees, can cause tree death that is amplified by insect mortality agents to propagate to patch and then landscape
or even regional-scale forest dieback. Severe drought and unusual warmth in the southwestern USA since the late 1990s apparently
exceeded species-specific physiological thresholds for multiple tree species, resulting in substantial vegetation mortality
across millions of hectares of woodlands and forests in recent years. Predictions of forest dieback across spatial scales
are constrained by uncertainties associated with: limited knowledge of species-specific physiological thresholds; individual
and site-specific variation in these mortality thresholds; and positive feedback loops between rapidly-responding insect herbivore
populations and their stressed plant hosts, sometimes resulting in nonlinear “pest” outbreak dynamics. Fire behavior also
exhibits nonlinearities across spatial scales, illustrated by changes in historic fire regimes where patch-scale grazing disturbance
led to regional-scale collapse of surface fire activity and subsequent recent increases in the scale of extreme fire events
in New Mexico. Vegetation dieback interacts with fire activity by modifying fuel amounts and configurations at multiple spatial
scales. Runoff and erosion processes are also subject to scale-dependent threshold behaviors, exemplified by ecohydrological
work in semiarid New Mexico watersheds showing how declines in ground surface cover lead to non-linear increases in bare patch
connectivity and thereby accelerated runoff and erosion at hillslope and watershed scales. Vegetation dieback, grazing, and
fire can change land surface properties and cross-scale hydrologic connectivities, directly altering ecohydrological patterns
of runoff and erosion. The interactions among disturbance processes across spatial scales can be key drivers in ecosystem
dynamics, as illustrated by these studies of recent landscape changes in northern New Mexico. To better anticipate and mitigate
accelerating human impacts to the planetary ecosystem at all spatial scales, improvements are needed in our conceptual and
quantitative understanding of cross-scale interactions among disturbance processes.
Management of forests for carbon uptake is an important tool in the effort to slow the increase in atmospheric CO2 and global warming. However, some current policies governing forest carbon credits actually promote avoidable CO2 release and punish actions that would increase long-term carbon storage. In fire-prone forests, management that reduces the risk of catastrophic carbon release resulting from stand-replacing wildfire is considered to be a CO2 source, according to current accounting practices, even though such management may actually increase long-term carbon storage. Examining four of the largest wildfires in the US in 2002, we found that, for forest land that experienced catastrophic stand-replacing fire, prior thinning would have reduced CO2 release from live tree biomass by as much as 98%. Altering carbon accounting practices for forests that have historically experienced frequent, low-severity fire could provide an incentive for forest managers to reduce the risk of catastrophic fire and associated large carbon release events.
The statistical aggregation of parasites among hosts is often described empirically by the negative binomial (Poisson-gamma) distribution. Alternatively, the Poisson-lognormal model can be used. This has the advantage that it can be fitted as a generalized linear mixed model, thereby quantifying the sources of aggregation in terms of both fixed and random effects. We give a worked example, assigning aggregation in the distribution of sheep ticks Ixodes ricinus on red grouse Lagopus lagopus scoticus chicks to temporal (year), spatial (altitude and location), brood and individual effects. Apparent aggregation among random individuals in random broods fell 8-fold when spatial and temporal effects had been accounted for.
This classic forest management text examines the ecology and silviculture of eucalypts in forests and plantations in Australia and overseas. The book presents approaches to the formulation of ecologically sustainable forest practices through a more fundamental understanding of Eucalyptus. The 14 chapters of the book are divided into three sections covering: the ecological background to silvicultural practice; the regeneration and continuing development of the forests; and silvicultural practice, including the current practices within the eucalypt forests.
Provides a synoptic description of the forests, with particular reference to the various eucalyptus species, and key environmental factors are identified. Fires in the upper canopy, undergrowth, litter, peat and soil-humus are described, and the effects of burning indicated. Pyric succession is noted, indicating the rich herb vegetation characteristic of the initial post-burn years, and the wet schlerophyll strategy is outlined. It seems paradoxical that forests producing vast amounts of fuel and generating the fiercest fires consist of fire-sensitive species, although the fact that they need to be burned at some time in their seed-bearing life is axiomatic. -P.J.Jarvis
Callitris intratropica R. T. Baker & H. G. Smith occurs in a range of environments throughout the lower latitudes of the Northern Territory. A geographic survey of the demographic structure of stands revealed a continuum ranging for populations which have a majority of dead individuals, a lack of regeneration and fire-scarred living adults, to stands with few dead or damaged individuals and a heaqvy stocking of juveniles. A TWINSPAN classification divided this continuum into four groups. There were no significant differences between the cover of rocks, grass or shrubs between the four groups of stands, nor was there a significant association with substrate type. Damaged stands were most common and occurred throughout the species' range, while the healthier stands were more typical on coastal sites with >30% tree canopy cover. Stands with dense regeneration were significantly associated with an area actively protected from fire by a forestry operation. A helicopter survey on parts of the remote and currently uninhabited Arnhem Land Plateau revealed a significantly greater count of dead stems than counts of living C. intratropica trees. Detailed studies at one site on the Arnhem Land Plateau showed that there is currently a high mortality of tagged stems, and that the abundant C. intratropica stags died since the 1940s. It is argued that the widespreadt crash of C. intratropica populations is a response to a change in fire regime associated with the coming of Europeans.
The contrasting regeneration outcomes of alpine ash (Eucalyptus delegatensis) and mountain ash (E. regnans) forests (collectively called ash) after the extensive and severe 2003, 2006/07 and 2009 bushfires in Victoria demonstrate the complexity of factors that influence the establishment of ash regeneration after bushfire. About 189 000 ha of ash forest was killed or severely damaged by the three bushfires, which burnt a land area totalling over 2.6 million ha. Silvicultural recovery work included aerial sowing of about 7100 ha of fire-killed regrowth in state forests with about 6400 kg of seed. This regrowth was less than 15–20 years of age and thus too immature to bear effective quantities of seed to achieve natural self-regeneration.This article includes a brief description of ash regeneration silviculture, a summary of relevant statistics for each of the three fires under consideration and the silvicultural recovery programs. Aspects of the recovery programs for the fires, including strategic seed-crop assessments, seedbed assessments, seed collection and management and aerial sowing operations are described, and their results are provided and discussed. The concept of ‘ecological stocking’, where regeneration levels are less than those required for commercial timber production, is also discussed.The natural seedling stocking levels resulting from the 2003 bushfires, which affected mostly alpine ash forests, were generally very satisfactory in stands of seed-bearing age. In contrast, after the bushfires of 2006/07, both natural and artificially sown eucalypt regeneration levels were often below commercial forestry standards. Natural stocking levels after the 2009 fires were again very satisfactory.
Large trees are critical components of forest ecosystems, but are declining in many forests worldwide. We predicted that growth of large trees is more vulnerable than that of small trees to high temperatures, because respiration and tissue maintenance costs increase with temperature more rapidly than does photosynthesis, and these costs may be disproportionately greater in large trees. Using 500,000 measurements of eucalypt growth across temperate Australia, we found that high temperatures do appear to impose a larger growth penalty on large trees than on small ones. Average stem diameter growth rates at 21° C compared with 11°C mean annual temperature were 57% lower for large trees (58 cm stem diameter), but only 29% lower for small trees (18 cm diameter). While our results are consistent with an impaired carbon budget for large trees at warmer sites, we cannot discount causes such as hydraulic stress. We conclude that slower growth rates will impede recovery from extreme events, exacerbating the effects of higher temperatures, increased drought stress and more frequent fire on the tall eucalypt forests of southern Australia. This article is protected by copyright. All rights reserved.
Climate change is causing fire regime shifts in ecosystems worldwide. Plant species with regeneration strategies strongly linked to a fire regime, such as obligate seeders, may be particularly threatened by these changes. It is unclear whether changes in fire regimes or the direct effects of climate change will be the dominant threats to obligate seeders in future. We investigated the relative importance of fire-related variables (fire return interval and fire severity) and environmental factors (climate and topography) on seedling establishment in the world’s tallest angiosperm, an obligate seeder, Eucalyptus regnans. Throughout its range, this species dominates the wet montane forests of south-eastern Australia and plays a keystone role in forest structure. Following major wildfires, we investigated seedling establishment in E. regnans within 1 year of fire as this is a critical stage in the regeneration niche of obligate seeders. Seedling presence and abundance were strongly related to the occurrence of fire but not to variation in fire severity (moderate vs. high severity). Seedling abundance increased with increasing fire return interval (range 26–300 years). First-year seedling establishment was also strongly associated with low temperatures and with high elevations, high precipitation and persistent soil water availability. Our results show that both climate and fire regimes are strong drivers of E. regnans seedling establishment. The predicted warming and drying of the climate might reduce the regeneration potential for some obligate seeders in future and these threats are likely to be compounded by changes in fire regimes, particularly increases in fire frequency.
Obligate seeder trees requiring high-severity fires to regenerate may be vulnerable to population collapse if fire frequency increases abruptly. We tested this proposition using a long-lived obligate seeding forest tree, alpine ash (Eucalyptus delegatensis), in the Australian Alps. Since 2002, 85% of the Alps bioregion has been burnt by several very large fires, tracking the regional trend of more frequent extreme fire weather. High-severity fires removed 25% of aboveground tree biomass, and switched fuel arrays from low loads of herbaceous and litter fuels to high loads of flammable shrubs and juvenile trees, priming regenerating stands for subsequent fires. Single high-severity fires caused adult mortality and triggered mass regeneration, but a second fire in quick succession killed 97% of the regenerating alpine ash. Our results indicate that without interventions to reduce fire severity, interactions between flammability of regenerating stands and increased extreme fire weather will eliminate much of the remaining mature alpine ash forest. This article is protected by copyright. All rights reserved.
Summary A technique developed for assessing seed crops in Eucalyptus regnans regrowth in Central Gippsland, Victoria, south-eastern Australia, has been adapted for use with three Lowland Sclerophyll Forest eucalypts from East Gippsland: E. sieberi, E. globoidea and E. baxteri. The technique was tested in the field by comparing the number of capsules assessed on two test trees of each species with the actual number of capsules counted on them, and by comparing the quantity of seed assessed on seedtrees retained in two harvested coupes with the subsequent seedfall from those trees. The results indicate that the technique can be used to assess seed crops on a stand basis with sufficient accuracy for field research purposes, although the assessment of individual trees is likely to be less precise.
Widespread climate change is expected to lead to altered patterns of disturbance, thereby driving future ecosystem change. This interaction, which is often poorly recognized or understood, may be particularly important in the sub-arctic due to rapid climate change and frequent fire. Our objective was to investigate how an altered fire return interval can interrupt successional pathways in a serotinous boreal ecosystem. We conducted this research in black spruce (Picea mariana [Mill] BSP) forests on the northern margin of the species’ distribution in Yukon Territory, Canada. We compared seed availability and seedling establishment of black spruce in stands of varying fire return interval using experimental manipulations within areas varying in their natural fire histories. Recruitment was drastically reduced following two closely timed fires, compared to stands burned under a typical fire return interval. However, recruitment was also limited in mature forest stands. On-site germination experiments demonstrated that black spruce recruitment was limited by seed availability after a short fire return interval, and by substrate quality in unburned stands. The vegetation of the boreal forest is thought to be highly resilient to climatic change, due in part to the adaptations that conifers have for post-fire regeneration. We show that shortened fire return intervals, through effects on seed availability, disrupt the normal sequence of post-fire recovery on seedbeds released by fire for colonisation. The results of this study provide strong empirical evidence that disturbance, although essential for stand renewal, may limit forest recovery or expansion when misaligned with reproductive cycles.
Abstract Plant responses to fire are variable between and within species and are influenced by numerous factors including fire severity. This study investigated the effects of fire severity on the regeneration and recruitment of forest eucalypts in the Cotter River Catchment, Australian Capital Territory (ACT). This study also examined the potential for the obligate seeder Eucalyptus delegatensis R.T. Baker (Myrtaceae) to expand into adjacent stands dominated by the facultative resprouter Eucalyptus fastigata H. Deane & Maiden (Myrtaceae) by seed shed and seedling establishment beyond the pre-fire boundary. Sites were located in areas of either higher or lower fire severity, and transects were placed across the boundary of stands of E. delegatensis and E. fastigata. Species distributions, tree survival and seedling densities and heights were recorded, and the location of each boundary was determined as the region of maximum change in species composition along the transects. Eucalyptus delegatensis was the only eucalypt killed by higher severity fire. However, E. delegatensis seedling density was greater at higher severity sites than lower severity sites. Eucalyptus fastigata seedling density was low across all sites, with other eucalypts producing few, if any, seedlings. There was no evidence that E. delegatensis had increased its range into downslope stands dominated by E. fastigata. Patterns of vegetative recovery and seedling recruitment may be related to a number of factors, including differences in allocation patterns between seeders and sprouters, and the effects of overstory and understory competition. It is unclear what processes impede E. delegatensis seedling establishment beyond the stand boundary, but may involve an inability of E. delegatensis to shed seed sufficiently far downslope; unsuitable conditions for germination beyond the boundary; or, competition from a retained or resprouting overstory, despite the potential for increased dispersal distance soon after fire.
1. The earliest examples of alternative community states in the literature appear to be descriptions of natural vegetation said to both depend on and promote fire. Nonetheless, alternative community states determined by fire have rarely been documented at landscape scales and in natural vegetation. This is because spatial autocorrelation may confound analyses, experimental manipulations are difficult and a long‐term perspective is needed to demonstrate that alternative community states can persist for multiple generations.
2. We hypothesized that alternative community states occur in a largely forested landscape in the Klamath Mountains, north‐western California, USA, where shrub‐dominated sclerophyllous vegetation establishes after fire that is lethal to forests. Forests redevelop if succession is not arrested by fire. Our hypothesis would require that sclerophyll and forest vegetation states each be maintained by different self‐reinforcing relationships with fire.
3. To test this hypothesis, we examined pyrogenicity of forest and sclerophyll vegetation as a function of time since the previous fire, accounting for spatial autocorrelation. Fire exclusion served as a de facto experimental treatment. Areas where fire had proceeded to occur served as controls.
4. Our findings are consistent with the occurrence of alternative community states established and maintained by different self‐reinforcing feedbacks with fire. Sclerophyll vegetation was more pyrogenic, especially where time‐since‐fire (TSF) was relatively short, a favourable relationship for this fire‐dependent vegetation. Forests were much less pyrogenic, especially where TSF was long, favouring their maintenance. Fire exclusion therefore has led to afforestation and rapid retreat of fire‐dependent vegetation.
5. Synthesis : We have documented how different self‐reinforcing combustion properties of forest and sclerophyll vegetation can naturally produce alternative states coexisting side‐by‐side in the same environment. Such fire‐mediated alternative states may be underappreciated, in part, because they are difficult to demonstrate definitively. In addition, the dynamics they exhibit contrast with common perceptions that fire hazard increases deterministically with TSF in forests and shrublands. Addressing the impacts of fire exclusion will probably require a management shift to better allow fire to perform its ecological role in shaping landscape diversity and maintaining fire‐dependent biota.
Clearfelling of wet eucalypt forest followed by high intensity burning and aerial sowing, a silvicultural system designed to mimic the natural dynamic of sporadic regeneration following cataclysmic disturbance, has attracted criticism for not maintaining the structural diversity that is associated with natural disturbance. A silvicultural systems trial was established at the Warra Long-Term Ecological Research site in southern Tasmania to explore alternatives to clearfelling in tall wet eucalypt forest. Stocking, density and growth of the seedling regeneration were monitored for up to 3 years after harvesting and regeneration treatments were applied from 1998 to 2007. The treatments were clearfell with understorey islands, a patchfell, stripfell, dispersed retention, aggregated retention, and single-tree/small-group selection. High intensity burning, low intensity burning and no burning were variously applied as part of these treatments.
We examined structural features of montane ash stands that varied from 15 to 300+ years of age in the Central Highlands of Victoria, south-eastern Australia. Extensive field data were gathered for our investigation and were drawn from >3700 survey plots on >625 sites located throughout the study region. Much of our study focussed on understorey features because extensive past studies in these forests have highlighted their importance as key habitat components for wildlife. A wide range of stand features, including the abundance of shrubs, the prevalence of tree ferns, the presence of Acacia spp., the presence of Myrtle Beech (Nothofagus cunninghamii), and the number of vegetation strata (a measure of vertical heterogeneity) varied considerably between age classes; most attributes were significantly (p < 0.001) less likely to occur or were significantly less abundant in young logged forests. Highly significant differences in these structural features also were found in stands dominated by different tree species (Mountain Ash [Eucalyptus regnans] and Alpine Ash [E. delegatensis]).
Climate Data Online. Climate Services, Bureau of Meteorology
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Model Selection and Multimodel Inference. A Practical Information-Theoretic Approach Buds, bushfires and resprouting in the eucalypts
- K P Burnham
- D R Anderson
Burnham, K.P., Anderson, D.R., 2002. Model Selection and Multimodel Inference. A Practical Information-Theoretic Approach. Springer, New York. Burrows, G.E., 2013. Buds, bushfires and resprouting in the eucalypts. Aust. J. Bot. 61, 331–349.
Eucalypt sowing and seedfall. Native Forest Silviculture Guideline No. 8. Department of Natural Resources and Environment Victoria
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Fagg, P.C., 2001. Eucalypt sowing and seedfall. Native Forest Silviculture Guideline No. 8. Department of Natural Resources and Environment Victoria, Melbourne.
The silviculture of Eucalyptus delegatensis. Part 1, Germination and dormancy
- R J Grose
Grose, R.J., 1963. The silviculture of Eucalyptus delegatensis. Part 1, Germination and dormancy. Bulletin Number 2. School of Forestry, University of Melbourne, Melbourne.
Discussion Paper on Ecological Stocking. Bushfire Recovery Project
- M Lutze
Lutze, M., 2011. Discussion Paper on Ecological Stocking. Bushfire Recovery Project 2006/07. Department of Sustainability and Environment Victoria, Melbourne.
Using Line Intersect Sampling for Coarse Woody Debris. British Columbia Ministry of Forests
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Marshall, P.L., Davis, G., LeMay, V.M., 2000. Using Line Intersect Sampling for Coarse Woody Debris. British Columbia Ministry of Forests, Vancouver.
Sowing Forests from the Air
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Assessing the vulnerability of Victoria's Central Highlands Forests to climate change
- C R Nitschke
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Nitschke, C.R., Hickey, G.M. 2007. Assessing the vulnerability of Victoria's Central Highlands Forests to climate change. Technical Report 1/2007. Prepared for the Department of Sustainability and Environment Victoria. School of Forest and Ecosystem Science, Melbourne University, Melbourne.
Forest Recovery after Bushfire. Department of Sustainability and Environment Victoria Big eucalypts grow more slowly in a warm climate: evidence of an interaction between tree size and temperature
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Poynter, M.J., Fagg, P.C., Bassett, O.D., Slijkerman, C., Lutze, M., 2009. Forest Recovery after Bushfire. Department of Sustainability and Environment Victoria, Melbourne. Prior, L.D., Bowman, D.M.J.S., 2014. Big eucalypts grow more slowly in a warm climate: evidence of an interaction between tree size and temperature. Glob. Change Biol. 20, 2793–2799.
Distribution of raw Eucalyptus seed using a helicopter-mounted sowing system
- N W Wilson
Wilson, N.W., 1993. Distribution of raw Eucalyptus seed using a helicopter-mounted sowing system. Forest Technical Report No. 11. Department of Conservation and Natural Resources Victoria, Melbourne.