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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.
... 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.
... A combination of high fire weather conditions and dry lightning storms resulted in extensive wildfires in 2003,2006,2009,2013,2014, burning over 97% of E. delegatensis distribution, in some case reburning areas two to three times ( Figure S1.42a). Other pulses include high temperature exposure and radiation frosts that can potentially damage post fire regeneration 45,46 . Annual rainfall fell within the lowest 1 percentile, representing an extreme value not seen in the baseline period (1961 -1988). ...
... A large proportion of E. delegatensis populations are currently in an immature stage following the 21 st century fires, rendering most populations vulnerable to local declines or extinction if reburnt, with consequent conversion to non-forest. The capacity of the species to recover is constrained because hotter and drier conditions reduce tree growth, seed production and seedling establishment 45,47,48 . Frost and high temperature exposure can also kill regeneration as well as result in abortion of flowers and fruits 48 . ...
... In areas where E. delegatensis regeneration has been killed it has been demonstrated that the species can be re-established by aerial sowing of seed 45 . This intervention is impractical if larger areas of forest are affected because of the costs of aerial sowing and the limited availability of seed. ...
... But for obligate seeders, the timing of the transition (phase change) to a reproductive state is particularly relevant, as these species may be susceptible to population declines and extinctions if they depend on a particular fire regime for regeneration (Stephens et al., 2013). In some cases, increasing fire frequencies threaten population persistence, with the age of reproductive maturity placing a critical lower threshold on the interval between fires that can be tolerated by a species (Bassett et al., 2015;Bowman et al., 2014;Keeley et al., 1999;Lindenmayer et al., 2011;Syphard et al., 2006). ...
... As all seed is stored in the canopy of mature mountain ash trees, the occurrence of tree-killing fires before the production of viable canopy seedbanks could cause the widespread collapse of mountain ash forest ecosystems ( Fig. 1) Gilbert, 1959;Lindenmayer, 2009b). Indeed, we have already begun to see large areas of forest dominated by obligate seeding species require artificial reseeding to maintain ecosystem persistence (Bassett et al., 2015;Fagg et al., 2013). In the context of reduced fire return intervals, the objectives of this study were to determine the extent to which relevant environmental variables influence the growth of tree height and stem diameter, and investigate how these size components interact with the environment to influence the age to seed production in mountain ash. ...
... Such changes to climatic niches are common in declining species and can plausibly result in extinctions (González-Orozco et al., 2016;Scheele et al., 2017). In the case of keystone species, these population declines will require costly human interventions, such as aerial seeding, to ensure that large areas of forest communities are not lost (Bassett et al., 2015). ...
Anthropogenic modifications to climate and natural fire regimes are occurring globally, leading to the production of environments that may be unsuitable for some species. Fire-intolerant plant species that rely on specific fire regimes for reproduction are at risk of population decline when successive fires occur in less than the time taken to produce seed. Quantifying key fire-related life history traits in such species is therefore critical for developing models of population viability, species distributions and ecosystem persistence.
We studied the Australian mountain ash (Eucalyptus regnans), the world’s tallest angiosperm and an ecologically and economically important keystone species. We tested whether mountain ash populations exhibit variation in susceptibility to increasing fire frequency by characterising the response of key vital rates to stand age (time since fire) under different environmental conditions.
We found that the time taken to produce seed varied geographically. Mean growth rates were greater in areas receiving higher levels of solar radiation, a trend that became stronger with tree age. Tree size and age had the strongest influence on the production of fruit capsules. Mature fruit capsules were found in trees as young as 11 years old, but stands may not contain reproductively viable seed crops until they are more than 21 years old.
Our results show that environmental factors influence the primary juvenile period of a keystone obligate seeder, in turn affecting the time taken for a population to develop a reproductively viable seed amount of seed. Reduced fire return intervals may therefore constrain the species’ realised niche (and geographic distribution) to areas where it can tolerate shorter fire return intervals due to faster growth and maturation. We suggest that populations of obligate seeders that reach reproductive viability faster are thus more likely to persist when exposed to multiple fires in short succession. Intra-stand variation in seed crops suggests that selection could also act on rapidly-maturing individuals, resulting in some populations exhibiting high levels of precocious reproductive activity.
... Currently, there is a poorly documented gap in our knowledge as to the actual viability and hence potential adaptive importance of this early flowering and fruiting trait in E. delegatensis and in the ash group eucalypts generally. In Victoria, local recruitment failure has occurred in some stands of alpine ash which have been burnt multiple timesup to three fires in 10 yearsin the past decade (Bowman Murphy et al. 2014) and in these cases, aerial seeding has been used to successfully reestablish stands (Bassett et al. 2015). However, if large scale landscape fire events burn through considerable areas of immature alpine ash regeneration, broad scale reseeding may prove problematic due to a lack of seed supplies (Ferguson 2011;Doherty et al. 2017). ...
... There is therefore a potential for this response trait to provide a buffering mechanism against the loss of some alpine ash populations to multiple short-interval fire events in some parts of the species range. Although the amount of regeneration under these circumstances may not be adequate from a silvicultural point of view (Fagg et al. 2013), it may be just adequate to allow the persistence of the species in less dense stands, satisfying a stocking standard suitable in a National Park context (Bassett et al. 2015). We are not suggesting that management of alpine ash stands needs to be relaxed in light of early viability; rather, that early viability may both explain the persistence of alpine ash in multiply burnt stands and also enable some management flexibility as regarding where and when to reseed stands. ...
... In particular, alpine ash stands burnt by high intensity fires in the Victorian Alps over the past 20 years provide a mosaic of recent fire histories within which to further examine the phenomenon. To date, several twice and thrice burnt alpine ash stands in Victoria have been artificially reseeded in order to enable regeneration (Fagg et al. 2013;Bassett et al. 2015). A comparison of the fate of any similar but untreated areas will be useful in order to gauge if any recruitment is occurring from early flowering individuals in non-reseeded stands. ...
Eucalyptus delegatensis R.T. Baker subsp. delegatensis is an interval-sensitive, fire-killed eucalypt that dominates large tracts of montane forest in the Australian Alps. Although it has been widely accepted in forest management that E. delegatensis takes 20 years to flower and fruit after stand-replacing fire events, recent observations after high intensity fires in the Australian Alps have shown that early flowering and fruiting is occurring from what can be termed ‘precocious’ individuals in some areas. In some instances, early flowering and fruit set is occurring within 6 years after stand-replacing fire. One historical study in the ACT had noted that such seed was viable, but we found no reported experiments documenting this or detailing the degree of viability. Here we discuss the results of a germination experiment undertaken on seed collected from Namadgi National Park from early-maturing alpine ash trees. Although at the low end of known viability estimates for E. delegatensis, seed from these individuals was nonetheless found to be viable, with a mean of 455 (SD = 139) germinants per 10 g of chaff and seed mix. We discuss this result in relation to fire management in the Australian Alps and suggest further research that needs to be undertaken to better document and understand the phenomenon.
... This transition has occurred in small areas that have been twice or thrice burnt since 2003 ( Fig. S1; Bowman et al. 2014). Recolonisation with ash requires either seed dispersal from adjacent unburnt areas (McCarthy et al. 1999) or aerial reseeding (Bassett et al. 2015). With increased fire frequency, Acacia shrubland may transition to grassland, based on evidence that multiple fires can reduce re-establishment of Acacia dealbata (Campbell and Kluge 1999). ...
... Managers have few interventions available: fuel load management with controlled burns, landscape-scale fire control, thinning to lower tree density and re-seeding (Table 1). Current practices favour interventions to maintain current states, such as aerial seeding of ash after fire (Bassett et al. 2015) or thinning to reduce fire risk and improve water yields (Ryan 2013). However, cost of re-seeding will eventually become prohibitive with increased extent of regrowth ash forest. ...
... In ash forests, more than one high intensity fire in 20 years is likely to cause extirpation, regardless of reduced growth, seed production or longer maturation caused by warmer, drier conditions. But an additional pressure on recruitment is relevant to the persistence of natural ash stands and re-seeding attempts: recruitment of alpine ash requires vernalisation of seed in its seedbed; 6 weeks near-freezing to break dormancy (Bassett et al. 2015). If soil moisture is limited during the austral spring germination period, or the soil surface exceeds 30-32°C, seeds may not germinate (Fagg et al. 2013). ...
In regions prone to wildfire, a major driver of ecosystem change is increased frequency and intensity of fire events caused by a warming, drying climate. Uncertainty over the nature and extent of change creates challenges for how to manage ecosystems subject to altered structure and function under climate change. Using montane forests in south-eastern Australia as a case study, we addressed this issue by developing an ecosystem state-and-transition model based on a synthesis of expert knowledge and published data, with fire frequency and intensity as drivers. We then used four steps to determine future adaptation options: (1) estimation of changes in ecosystem services under each ecosystem state to identify adaptation services: the ecosystem processes and services that help people adapt to environmental change; (2) identification and sequencing of decision points to maintain each ecosystem state or allow transition to an alternative state; (3) analysis of interactions between societal values, scientific and management knowledge and institutional rules (vrk) required to reframe the decision context for future management, and (4) determining options for an adaptation pathway for management of montane forests under climate change. Our approach is transferable to other ecosystems for which alternative states can be predicted under climate change.
... 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.
... Two possible explanations can account for the response of NO x to discharge. The elevated NO x could be due in part to the occurrence of a wildfire in January 2013 that burnt 15,353 ha of alpine ash forest (Eucalyptus delegatensis) near Harrietville (reach 1) (Bassett et al. 2015). 88% of this fire occurred within the Alpine national park which is the major source of runoff to the Ovens River at Harrietville (Bassett et al. 2015). ...
... The elevated NO x could be due in part to the occurrence of a wildfire in January 2013 that burnt 15,353 ha of alpine ash forest (Eucalyptus delegatensis) near Harrietville (reach 1) (Bassett et al. 2015). 88% of this fire occurred within the Alpine national park which is the major source of runoff to the Ovens River at Harrietville (Bassett et al. 2015). Our sampling excursion occurred after the peak flow and it is possible that the strong continuous increase in concentration represents a NO x pulse travelling down the river. ...
Dissolved organic nitrogen (DON) can comprise up to 80% of the dissolved N pool in riverine ecosystems, but concentration and compositional responses to catchment conditions has received limited attention. We examined the suite of nitrogenous nutrients along the length of the Ovens River, Victoria, Australia, a river with identifiable regions of native vegetation, agricultural activity and floodplain forest connection, carrying out longitudinal surveys in winter during a period of high flow and in summer during a period of stable base flow. We examined: the concentrations of DON, the proportion of DON that occurs as dissolved combined amino acids (DCAAs), whether concentration and DCAA composition varied between flow and whether land-use and tributaries have an impact upon nutrient concentration and DON composition. DON concentrations were greater than dissolved inorganic nitrogen under both base flow and high flow conditions. Under base flow DON exhibited a continuous increase in concentration downstream (ranging from 50 to 300 μg/L), compared to a much larger increase under high flow (150–600 μg/L) coupled with a major discrete increase of ~ 350 μg/L at a tributary input (King River). Concentrations of NOx (oxides of nitrogen) species were much higher under high flow conditions (range 50–250 μg/L) compared to 0–50 µg/L at base flow, and showed a significant increase in concentration with distance downstream. A discrete change in NOx concentrations was also observed at the King River confluence under high flow, although in this case causing a decrease in concentration of ~100 µg/L. DCAA concentrations varied little along the length of the river at base flow but increased with distance downstream at high flow. The DCAA concentrations were of the same order of magnitude as ammonium at both base and high flows and nitrate concentrations at base flow. The proportion of DON that was in the form of DCAA was reasonably uniform during high flow (3–6%), but highly variable at base flow (5–44%). The amino acid (AA) composition of the DCAA varied along the river and differed between flow regimes (except below the confluence with the King River where AA composition under the two flow conditions converged) suggesting a strong influence of land use. We show that DON is potentially a large component (4–81%) of the total N budget and given that 5–23% is in the form of peptide/protein, represents an important source of N. DON and more specifically DCAAs should therefore be considered both when constructing N budgets and monitoring levels of in-stream nitrogen.
... If fire intervals are shorter than the time required for regenerating seedlings to reach reproductive maturity (c. 20 years) then local populations collapse, resulting in local extinction of the ash eucalypts (Bassett et al., 2015). Ash eucalypts do not have a soil seedbank, so regeneration on sites where local populations have collapsed depends on dispersal of seeds from adjacent trees (Fig. 2a). ...
... Mitigating the effect of climate-driven fires on obligate seeder forests constitutes an enormous challenge to land managers given that fuel treatments are likely to be ineffective under extreme fire conditions (Price & Bradstock, 2012;Fairman et al., 2015). While reseeding of thrice-burnt forests has re-established obligate seeders where population collapse has occurred (Bassett et al., 2015), this is unlikely to be possible should large areas of forest be lost, due to inadequate seed supplies and the costs of aerial sowing (Ferguson, 2011). ...
Forests that regenerate exclusively from seed following high-severity fire are particularly vulnerable to local extinction if fire frequency leaves insufficient time for regenerating plants to reach sexual maturity. We evaluate the relative importance of extrinsic (such as fire weather and climate cycles) and intrinsic (such as proneness to fire due to stand age and structural development) factors in driving the decline of obligate seeder forests. We illustrate this using obligate seeding alpine ash (Eucalyptus delegatensis) forests in the montane regions of Victoria, Australia, that were burnt by megafires in 2003 (142,256 ha) or 2007 (79,902 ha), including some twice-burnt areas (11,599 ha). Geospatial analyses showed only a small effect of stand age on the remote sensing estimates of crown defoliation, but a substantial effect of forest fire weather, as measured by forest fire danger index (FFDI). Analysis of meteorological data over the last century showed that 5-year increases in FFDI precede cycle major fires in the E. delegatensis forests. Such strong extrinsic climate/weather driving of high-severity fires is consistent with the 'interval squeeze model' that postulates the vulnerability of obligate seeder forests to landscape-scale demographic collapse in response to worsening fire weather under climate change.
... Following the 2013 wildfires in the Australian Alps bioregion an estimated 45 000 ha of forest dominated by obligate seeders and over 300 000 ha of resprouter-dominated forests were burned twice within a 10-year period (Fairman et al. 2015). Though there was a high level of natural regeneration of eucalypts following the 2003 and 2009 fires, supplementary seeding across all tenures ensured eucalypt regeneration following the 2006-07 'Great Divide' fires and again following the 2013 'Harrietville' fires (Fagg et al. 2013;Bassett et al. 2015). Taylor et al. (2014) found that fire severity was higher in 7-36 year old stands than in stands younger or older than this in an E. regnans forest burnt in the February 2009 fires. ...
... These actions will need to be carried out on areas with forest types not targeted for commercial wood utilisation. Restoring degraded or deforested areas in noncommercial upland areas following fires is technically feasible (Bassett et al. 2015) and will probably be socially acceptable but will require significant investment. ...
Australia has a highly diverse and variable climate and its forests are well-adapted to climatic variation. However, human-induced changes in climate could exceed historical ranges of variability and have effects on forests well beyond the experience of forest managers. These conditions will require implementation of management practices appropriate to a changing climate but there has been little analysis of potential management options for Australian native forests. The paper analyses potential management options for the tall, wet eucalypt forests in Victoria’s Central Highlands. This region has already experienced a strong drying and warming trend and a high incidence of severe bushfires over the last 15 years. Future changes are likely to include rising CO2, increasing temperatures and an overall decrease and changing seasonal patterns in rainfall. This is likely to result in higher fire danger weather conditions, changes in phenology of flowering, seeding and germination and shifts in forest composition and productivity. A range of different management options were considered and analysed in terms of current practice, costs and implementation feasibility. Many management actions identified to support adaptation to climate change were assessed as currently being implemented as part of sustainable forest management arrangements. Options that are not generally currently implemented include developing gene management programs and off-site gene banks, ex-situ conservation and increasing cooperation in species management, increasing stand and regional species diversity, identification and deployment of more drought- or disturbance-tolerant species or genotypes, planning to reduce disease losses through monitoring and sanitation harvests, managing stand structure to reduce impacts on water availability and implementing silvicultural techniques to promote stand vigour, as practised elsewhere in Australia. The likelihood of more intense rainfall events will require changes to infrastructure, such as forest road design and construction specifications. Implementing adaptation will require new approaches to forest management, potentially involving significant human intervention, new ecological, environmental and social research, new modes of communication with the public, new policies and revised regulations and management prescriptions.
... We have identified that there is a level of uncertainty regarding the permanence of shifts from eucalypt to non-eucalypt states (grey dashed lines , Figs 4a, b), echoing the longidentified issues of judging ecological stability or persistence at differing temporal and spatial scales (Connell and Sousa 1983). In some instances, it has been demonstrated that fire can drive a permanent shift to non-forest (Fletcher et al. 2014); however, over shorter periods and in other fire-dependent biomes, it has been shown that non-forest areas can revert to forest in the presence of (a) suitable fire regimes (Staver et al. 2011;Ratajczak et al. 2014); (b) environmental conditions that favour increased growth (Murphy and Bowman 2012), thereby decreasing the time to develop fire-resistant structures or reach escape size (particularly in resprouter forests, Fig. 4b); or (c) targeted management intervention, for example, reforestation efforts discussed by McKimm and Flinn (1979), Ashton and Chappill (1989), Ashton (2000b) and Bassett et al. (2015). ...
... The effects of recent recurrent wildfires on obligate seeder eucalypt forests in south-eastern Australia have led to suggestions of management interventions to limit or reverse their 'demographic collapse' (Bowman et al. 2013;Bowman et al. 2014). A recent case study of E. delegatensis forests indicated potential for artificial sowing to establish tree seedling cohorts in repeatedly burned areas, albeit at lower densities than those in naturally seeded once-burned areas (Bassett et al. 2015). However, if wildfires increase in extent and frequency -as is predicted for this region and many others around the world (Girardin et al. 2010) -a critical challenge will be to maintain sufficient stocks of viable seeds to artificially sow large areas. ...
In temperate Australia, wildfires are predicted to be more frequent and severe under climate change. This could lead to marked changes in tree mortality and regeneration in the region's predominant eucalypt forests, which have been burned repeatedly by extensive wildfires in the period 2003–14. Recent studies have applied alternative stable state models to select 'fire sensitive' forest types, but comparable models have not been rigorously examined in relation to the more extensive 'fire tolerant' forests in the region. We review the effects of increasing wildfire frequency on tree mortality and regeneration in temperate forests of Victoria, southeastern Australia, based on the functional traits of the dominant eucalypts: those that are typically killed by wildfire to regenerate from seed ('obligate seeders') and those that mostly survive to resprout ('resprouters'). In Victoria, over 4.3 million ha of eucalypt forest has been burned by wildfire in the last decade (2003–14), roughly equivalent to the cumulative area burned in the previous 50 years (1952–2002; 4.4 million ha). This increased wildfire activity has occurred regardless of several advancements in fire management, and has resulted in over 350 000 ha of eucalypt forest being burned twice or more by wildfire at short (#11 year) intervals. Historical and recent evidence indicates that recurrent wildfires threaten the persistence of the 'fire sensitive' obligate seeder eucalypt forests, which can facilitate a shift to non-forest states if successive fires occur within the trees' primary juvenile period (1–20 years). Our review also highlights potential for structural and state changes in the 'fire tolerant' resprouter forests, particularly if recurrent severe wildfires kill seedlings and increase tree mortality. We present conceptual models of state changes in temperate eucalypt forests with increasing wildfire frequency, and highlight knowledge gaps relating to the development and persistence of alternative states driven by changes in fire regimes.
... 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 southeastern 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 southeastern 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.
... In some cases, proactive intervention after an extreme event may prevent system collapse or mitigate the impact of the next extreme event. Firekilled regeneration in Alpine Ash forest has been re-established by the aerial sowing of seed 81 , for example, although it is expensive, dependant on seed availability and long-term establishment will be compromised by subsequent fires and reduced growth rates 28 . In other instances, however, management responses will be limited because the ecosystems are too remote, intervention would be too expensive, or success would be low (for example, replanting mangroves in the Gulf of Carpentaria). ...
In the version of this Perspective originally published, affiliations 1 and 4 ware incorrect, and should have read: “¹Antarctic Climate & Ecosystems CRC, University of Tasmania, Hobart, Tasmania, Australia” and “⁴Centre for Water, Climate and Land (CWCL), University of Newcastle, Callaghan, NSW, Australia”. These have been corrected in the online versions of this Perspective.
... In some cases, proactive intervention after an extreme event may prevent system collapse or mitigate the impact of the next extreme event. Firekilled regeneration in Alpine Ash forest has been re-established by the aerial sowing of seed 81 , for example, although it is expensive, dependant on seed availability and long-term establishment will be compromised by subsequent fires and reduced growth rates 28 . In other instances, however, management responses will be limited because the ecosystems are too remote, intervention would be too expensive, or success would be low (for example, replanting mangroves in the Gulf of Carpentaria). ...
The interaction of gradual climate trends and extreme weather events since the turn of the century has triggered complex and, in some cases, catastrophic ecological responses around the world. We illustrate this using Australian examples within a press-pulse framework. Despite the Australian biota being adapted to high natural climate variability, recent combinations of climatic presses and pulses have led to population collapses, loss of relictual communities and shifts into novel ecosystems. These changes have been sudden and unpredictable, and may represent permanent transitions to new ecosystem states without adaptive management interventions. The press-pulse framework helps illuminate biological responses to climate change, grounds debate about suitable management interventions and highlights possible consequences of (non-) intervention.
... Obviously, aerial seeding of H. laeve was successful and had stimulated succession in Mu Us Sandy Land. Similar results had also been obtained in Australia [29], United States [12,13], Iceland [10] and Canada [30]. ...
Desertification is a global and pressing environmental problem in the course of environmental changes, and considerable efforts have been made to restore these degraded ecosystems. Aerial seeding has been widely used to accelerate ecological restoration around the world. However, few efforts have been made to assess the ecosystem service function after aerial seeding has occurred. In this study, we analyzed variations in the ecosystem service function after varying periods of elapsed time after aerial seeding of Hedysarum laeve Maxim. (14a, 30a and 38a) in the Mu Us Sandy Land, China. We also assessed the carbon sequestration ability, biodiversity, soil properties, wind-break and sand-fixation ability on a typical windward slope. We found that the overall assessment value of ecosystem services had generally increased with the elapsed time after aerial seeding. Additionally, the assessment values increased as the slope position moved downwards. Moreover, we observed a gradual replacement of H. laeve by Artemisia ordosica Krasch and grass species with the increase in elapsed years after aerial seeding, indicating a positive succession towards locally native vegetation. Compared with the local natural vegetation, our results suggest that the practice of aerial seeding stimulated vegetation restoration without the need for follow-up field interventions, and the practice of aerial seeding might fit more ecosystems with similar vegetation degradation problems.
... All rights reserved. seeding programs that have already been trialled for fire-sensitive eucalypt forests (Bassett et al. 2015). ...
The carbon stability of fire-tolerant forests is often assumed but less frequently assessed, limiting potential to anticipate threats to forest carbon posed by predicted increases in forest fire activity. Assessing the carbon stability of fire-tolerant forests requires multi-indicator approaches that recognise the myriad of ways that fires influence the carbon balance including combustion, deposition of pyrogenic material, and tree death, post-fire decomposition, recruitment, and growth. Five years after a large-scale wildfire in south-eastern Australia, we assessed the impacts of low- and high-severity wildfire, with and without prescribed fire (≤ 10 years before), on carbon stocks in multiple pools, and on carbon stability indicators (carbon stock percentages in live trees and in small trees, and carbon stocks in char and fuels) in fire-tolerant eucalypt forests. Relative to unburnt forest, high-severity wildfire decreased short-term (five-year) carbon stability by significantly decreasing live tree carbon stocks and percentage stocks in live standing trees (reflecting elevated tree mortality), by increasing the percentage of live tree carbon in small trees (those vulnerable to the next fire), and by potentially increasing the probability of another fire through increased elevated fine fuel loads. In contrast, low-severity wildfire enhanced carbon stability by having negligible effects on above-ground stocks and indicators, and by significantly increasing carbon stocks in char and, in particular, soils, indicating pyrogenic carbon accumulation. Overall, recent preceding prescribed fire did not markedly influence wildfire effects on short-term carbon stability at stand scales. Despite wide confidence intervals around mean stock differences – indicating uncertainty about the magnitude of fire effects in these natural forests – our assessment highlights the need for active management of carbon assets in fire-tolerant eucalypt forests under contemporary fire regimes. Decreased live tree carbon and increased reliance on younger cohorts for carbon recovery after high-severity wildfire, could increase vulnerabilities to imminent fires, leading to decisions about interventions to maintain the productivity of some stands. Our multi-indicator assessment also highlights the importance of considering all carbon pools, particularly pyrogenic reservoirs like soils, when evaluating the potential for prescribed fire regimes to mitigate the carbon costs of wildfires in fire-prone landscapes. This article is protected by copyright. All rights reserved.
... This has occurred in recent years in the higher elevation Alpine ash forests (E. delegatensis) (Bowman et al., 2014;Bassett et al., 2015). Little is known about how the flammability of these wet forests changes as a result of fire. ...
Fuel moisture is a key driver of forest flammability as it influences ignition likelihood, fire intensity and resultant fire severity. Changes to forest canopy cover following disturbances like wildfire or logging may alter forest flammability by changing the microclimatic conditions that influence fine fuel moisture. Wet forests dominated by Mountain Ash (Eucalyptus regnans) are highly valued for their flora and fauna, timber, carbon and water. Wildfires are an important part of the lifecycle of these forests, but too frequent fire can threaten post-fire regeneration. With large tracts of Mountain Ash forest recovering from recent wildfires (in 2009 and 1983) there is a need to understand the mechanisms driving flammability in these forests, particularly as the forest structure changes following fire. This study sought to understand the effects of fire history on the flammability of Mountain Ash forests by specifically considering fuel moisture for different times since fire and fire severities. We measured canopy cover (plant area index) and fuel moisture within 8 forest sites last burnt between 7 and 200 years ago by wildfires of low or high severity. Fuel moisture and fuel availability (i.e. number of days when fine fuels are dry enough to ignite and sustain spreading fire) were strongly associated with canopy cover; with denser canopied forests having higher fuel moisture. The largest differences in canopy cover occurred between the recently burnt high and low severity forests. For the longer-unburnt forests there were no systematic differences evident in canopy cover with time since fire or fire severity. The fuel moisture was higher and fuels only available to burn on one day in the forest recently burnt by high severity fire (in association with a dense canopy). In contrast, fuels were drier and available to burn on 238 days in the forest recently burnt by low severity fire (in association with a sparser canopy). For the longer-unburnt forests (33 or more years since fire) there were no clear trends between fuel moisture and time since fire and fire severity suggesting that fires do not have a lasting impact on fuel moisture within these wet forests. Overall, this study shows that wildfires have immediate impacts on fuel moisture in Mountain Ash forests but as the time since fire increases, moisture appears to be more a function of canopy properties than fire history.
... Aerially broadcasting seed may be an option for reintroducing kahikatea propagules to large areas without disturbing plant communities. This method has been successfully employed for restoration purposes in other countries (Bassett et al. 2015;Xiao et al. 2015). ...
Grey willow (Salix cinerea) is widely established in New Zealand’s remaining swamps and fens, and in many areas has replaced endemic kahikatea (Dacrycarpus dacrydioides) forest. Conservation managers need to know how to restore willow-invaded wetlands to a resilient natural state, but knowledge on how to achieve this goal is limited. We planted kahikatea seedlings into an intact stand of grey willow and into areas where the herbicides glyphosate or triclopyr had been aerially applied to control willow ~1.5 years earlier. We measured canopy cover, light availability and the growth of planted kahikatea. In areas treated with glyphosate, grey willow canopy cover was reduced to 44% ± 3.7% (95% confidence interval), light availability increased to 64% ± 15% of full sunlight, and kahikatea grew an average of 44 cm ± 11.7 cm in 14 months. In contrast, there was little or no kahikatea growth under the intact willow canopy or in the triclopyr treatment area where grey willow canopy cover remained high and mean light availability was low (25% ± 4% of full sunlight). We conclude that the removal of the grey willow canopy through aerial glyphosate application created favourable conditions for the growth of planted kahikatea and may enable the restoration of kahikatea forest in wetlands dominated by grey willow.
... In montane forest ecosystems in mainland southeastern Australia (Australian Capital Territory, New South Wales and Victoria), particularly the commercial fire-killed ash forest types dominated by Eucalyptus regnans F. Muell. (mountain ash) and Eucalyptus delegatensis R. Baker (alpine ash), there has been a reliance on manually re-seeding both after commercial timber harvesting and after multiple short interval fires where regeneration has failed (Bowman et al. 2014;Bassett et al. 2015). However, if areas affected by changing fire regimes substantially increase and management response cannot cope with the scale and degree of change, ecosystems may be shifted to undesirable states where the supply of ecosystem services is compromised. ...
Forest ecosystems and their associated natural, cultural and economic values are highly vulnerable to climate driven changes in fire regimes. A detailed knowledge of forest ecosystem responses to altered fire regimes is a necessary underpinning to inform options for adaptive responses under climate change, as well as for providing a basis for understanding how patterns of distribution of vegetation communities that comprise montane forest ecosystems may change in the future. Unplanned consequential adaptation of both natural and human systems, i.e. autonomous adaptation, will occur without planned intervention, with potentially negative impacts on ecosystem services. The persistence of forest stands under changing fire regimes and the maintenance of the ecosystem services that they provide pivot upon underlying response traits, such as the ability to resprout, that determine the degree to which composition, structure and function are likely to change. The integration of ecosystem dynamics into conceptual models and their use in exploring adaptation pathways provides options for policy makers and managers to move from autonomous to planned adaptation responses. Understanding where autonomous adaptation provides a benefit and where it proves potentially undesirable is essential to inform adaptation choices. Plausible scenarios of ecological change can be developed to improve an understanding of the nature and timing of interventions and their consequences, well before natural and human systems autonomously adapt in ways that may be detrimental to the long-term provision of ecosystem services. We explore the utility of this approach using examples from temperate montane forest ecosystems of southeastern Australia.
... However, extensive use of prescribed fires will need careful consideration of the fire intervals required to maintain new cohorts of eucalypt stems, including intervals close to the minimum tolerable fire interval for these forests (c. 15 years; Cheal, 2010), and/or a diversity of intervals within any given landscape as non-burnt patches within prescribed fire boundaries or using a mosaic of prescribed fire intervals at broader scales (Burrows, 2008). If tree mortality is increased in extent by, for example, two wildfires in quick succession, management options might need to include re-seeding the dominant eucalypts in mixed-species forests in a manner akin to the fire-sensitive 'ash-type' eucalypt forests dominated by obligate seeder trees (Bassett et al., 2015b). That is, rather than assuming perpetual resistance and resilience to fire, our study highlights the need to carefully monitor tree population dynamics in even the most fire-tolerant forests, particularly in light of the many emerging threats to forest health posed by changing disturbance and climate regimes (Millar and Stephenson, 2015). ...
Mixed-species eucalypt forests of temperate Australia are assumed tolerant of most fire regimes based on the impressive capacity of the dominant eucalypts to resprout. However, empirical data to test this assumption are rare, limiting capacity to predict forest tolerance to emerging fire regimes including more frequent severe wildfires and extensive use of prescribed fire. We quantified tree mortality and regeneration in mixed-species eucalypt forests five years after an extensive wildfire that burnt under extreme fire weather. To examine combined site-level effects of wildfire and prescribed fire, our study included factorial replications of three wildfire severities, assessed as crown scorch and understorey consumption shortly after the wildfire (Unburnt, Low, High), and two times since last preceding fire (<10 years since prescribed fire, >30 years since any fire). Our data indicate that while most trees survived low-severity wildfire through epicormic resprouting, this capacity was tested by high-severity wildfire. Five years after the wildfire, percentage mortalities of eucalypts in all size intervals from 10 to >70 cm diameter were significantly greater at High severity than Unburnt or Low severity sites, and included the near loss of the 10 to 20 cm cohort (93% mortality). Prolific seedling regeneration at High severity sites, and unreliable basal resprouting, indicated the importance of seedling recruitment to the resilience of these fire-tolerant forests. Recent prescribed fire had no clear effect on forest resistance (as tree survival) to wildfire, but decreased site-level resilience (as recruitment) by increasing mortalities of small stems. Our study indicates that high-severity wildfire has the potential to cause transitions to more open, simplified stand structures through increased tree mortality, including disproportionate losses in some size cohorts. Dependence on seedling recruitment could increase vulnerabilities to subsequent fires and future climates, potentially requiring direct management interventions to bolster forest resilience.
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.
Direct seeding has been considered a forest restoration option for centuries. Over the past half century, the use of this practice has declined in developed countries as forest regeneration programs have advanced with the production of quality seedlings that can successfully establish restoration sites. Direct seeding is being reconsidered as a restoration option as the potential size of the worldwide forest restoration program has grown because of massive deforestation in third-world nations and due to global climate change. This review examines direct seeding from a number of perspectives. First, merits of using this practice in restoration programs are defined. Major merits of this option are that it can be done quickly, over hard to reach and large disturbed areas, and at a relatively low cost. Second, current research findings from restoration programs are discussed. The major finding is that seedling establishment rates are low (i.e. typically around 20% of seeds planted) due to site conditions, seed predation and vegetation competition, and field performance (i.e. survival and growth) is lower than planted seedlings. Third, operational practices for the application in restoration programs are reviewed. To successfully conduct direct seeding programs practitioners need to consider seedbed receptivity, seed distribution and seeding rate. Fourth, potential new practices are presented. Some of these new practices attempt to create a more effective means to disperse seed across the site, minimize seed predation or create a more favorable microsite environment. This review provides a synthesis of what is known about direct seeding, thereby allowing practitioners to make a rational decision of whether to apply this practice towards their forest restoration program. Contents 1 In trod u ct ion 2 Me rit s o f D ir e ct Se ed in g as a Re fo r e stat ion Op t i on 2. 1 E col og ica l 2. 2 Bio lo gi cal-R oot Sy st e m For m 2. 3 E con o m ic 2. 4 Op e rat ion a l 3 Cu r re n t Dir e ct S ee d in g R e s ea rch 3. 1 Con v er s ion Rat e s 3. 2 Fac tor s A f fe ct in g C on ve rs ion Rat e s AR TI CL E IN FO Citation: Grossnickle SC, Ivetić V (2017) Direct Seeding in Reforestation-A Field Performance Review. Reforesta 4: 94-142.
Forest mega-fires have become a global phenomenon in recent decades including in south-eastern Australia where large areas of forest have been fire-killed with loss of human lives and property and impacting carbon sequestration and greenhouse gas emissions. The vast extent and impact of mega-fires has induced a re-evaluation of fuel reduction methods as a key management strategy in wildfire risk mitigation in many countries. This study investigated the impact of a commercial thinning in Eucalyptus delegatensis forest on fuel hazard, fuel loads and wildfire behaviour, eight years after completion of a bay and outrow thinning operation. At the stand level, thinning reduced overstorey tree stocking by more than 50%, increased canopy openness and stimulated the growth of retained trees. Thinning also encouraged the profuse regeneration of over 1000 saplings ha⁻¹ of E. delegatensis, mostly in the outrows, compared with no sapling regeneration in unthinned forest. A system of additive biomass equations was developed to estimate total biomass and component biomass (stem wood, bark, branches and foliage) of individual trees. The aboveground tree carbon was 433 ± 49 Mg C ha⁻¹ in unthinned forest and 322 ± 47 Mg C ha⁻¹ in thinned forest. Thinning decreased surface fuel hazard ratings and fuel loads but had no significant effect on the mass of coarse woody fuels. Fire simulation under severe to extreme weather conditions, as occurred in the 2006/7 Great Divide Fires, indicated an almost 30% reduction in fireline intensity and about 20% reduction in the rate of spread and spotting distance in thinned forest compared with unthinned forest. This study indicates the potential of thinning to reduce wildfire severity and to increase the fire-survival of E. delegatensis.
Understanding the impacts of natural and human disturbances on forest biota is critical for improving forest management. Many studies have examined the separate impacts on fauna and flora of wildfire, conventional logging, and salvage logging, but empirical comparisons across a broad gradient of simultaneous disturbances are lacking. We quantified species richness and frequency of occurrence of vascular plants, and functional group responses, across a gradient of disturbances that occurred concurrently in 2009 in the mountain ash forests of southeastern Australia. Our study encompassed replicated sites in undisturbed forest (∼70 yr post fire), forest burned at low severity, forest burned at high severity, unburned forest that was clearcut logged, and forest burned at high severity that was clearcut salvage logged post-fire. All sites were sampled 2 and 3 yr post fire. Mean species richness decreased across the disturbance gradient from 30.1 species/site on low-severity burned sites and 28.9 species/site on high-severity burned sites, to 25.1 species/site on clearcut sites and 21.7 species/site on salvage logged sites. Low-severity burned sites were significantly more species-rich than clearcut sites and salvage logged sites; high-severity burned sites supported greater species richness than salvage logged sites. Specific traits influenced species' sensitivity to disturbance. Resprouting species dominated undisturbed mountain ash forests, but declined significantly across the gradient. Fern and midstory trees decreased significantly in frequency of occurrence across the gradient. Ferns (excluding bracken) decreased from 34% of plants in undisturbed forest to 3% on salvage logged sites. High-severity burned sites supported a greater frequency of occurrence and species richness of midstory trees compared to clearcut and salvage logged sites. Salvage logging supported fewer midstory trees than any other disturbance category, and were distinctly different from clearcut sites. Plant life form groups, including midstory trees, shrubs, and ferns, were dominated by very few species on logged sites. The differences in biotic response across the gradient of natural and human disturbances have significant management implications, particularly the need to reduce mechanical disturbance overall and to leave specific areas with no mechanical disturbance across the cut area during logging operations, to ensure the persistence of resprouting taxa.
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.
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
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.
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.