Too much, too soon? A review of the effects of increasing wildfire frequency on tree mortality and regeneration in temperate eucalypt forests

2016 ◽  
Vol 25 (8) ◽  
pp. 831 ◽  
Author(s):  
Thomas A. Fairman ◽  
Craig R. Nitschke ◽  
Lauren T. Bennett
Keyword(s):  
Tree Mortality ◽  
Stable State ◽  
Alternative Stable State ◽  
Juvenile Period ◽  
Eucalypt Forest ◽  
Eastern Australia ◽  
State Changes ◽  
State Models ◽  
Eucalypt Forests ◽  
In Fire

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, south-eastern 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.

Transpiration by Trees From Contrasting Forest Types

1996 ◽  
Vol 44 (3) ◽  
pp. 249 ◽  
Author(s):  
DJ Barrett ◽  
TJ Hatton ◽  
JE Ash ◽  
MC Ball
Keyword(s):  
Leaf Area ◽  
Transpiration Rate ◽  
Sap Flow ◽  
Crown Area ◽  
Moisture Contents ◽  
South Eastern ◽  
Eucalypt Forest ◽  
Eastern Australia ◽  
Southern Aspect ◽  
Eucalypt Forests

Temperate rainforests and eucalypt forests of coastal south-eastern Australia are distributed differentially with aspect. Rainforests, in which Ceratopetalum apetalum D.Don and Doryphora sassafras Endl. are the dominant tree species, occur on slopes of southerly aspect and along gully bottoms, whereas eucalypt forests, dominated by Eucalyptus maculata Hook., occur on upper slopes of northerly aspect and on ridge tops. Whether transpiration rates of trees differed across the rainforest-eucalypt forest boundary on north and south facing aspects was tested by measuring stem sap flow in trees in a single catchment during winter, summer and autumn. Differences in transpiration rate by trees in these stands were due to various combinations of biological and physical factors. Firstly, mean maximum transpiration rate per tree (crown area basis) was greater in rainforest on the gully bottom where deep soil water from down-slope drainage was greater than in eucalypt forest located upslope on the northern aspect. By contrast, there was no difference between maximum transpiration rates in rainforest and eucalypt forest on the southern aspect. Variation in transpiration rate between seasons was not related to variation in surface soil moisture content (< 0.35 m depth). Secondly, transpiration rates per unit crown area in rainforest at the gully bottom were associated with higher leaf area indices than upslope on the northern aspect. However, in rainforest upslope on the southern aspect, higher transpiration rates were not associated with higher leaf area indices. Thirdly, trees in eucalypt forest maintained similar sapwood moisture contents in summer as in winter and autumn, whereas sapwood moisture contents declined in rainforest trees in summer, suggesting that eucalypts had access to water from deep within the soil profile which was unavailable to more shallow rooting rainforest trees. Fourthly, higher modal and maximal sap velocities in eucalypt trees were partly due to wider xylem vessels and resulted in faster maximum sap flow and greater daily total water use in all seasons on both aspects than in rainforest species. Finally, as atmospheric demand for water increased from winter to summer, transpiration rates were mediated by stomata1 closure as indicated by lower average midday shoot conductance to water vapour during summer than other seasons. The interaction between microenvironment, which deteimines water availability, and physiological attsibutes, which determine tree water acquisition and use, may contribute to the differential distribution of rainforest and eucalypt forest with aspect in south-eastern Australia.

scholarly journals The Effect of Antecedent Fire Severity on Reburn Severity and Fuel Structure in a Resprouting Eucalypt Forest in Victoria, Australia

Forests ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 450
Author(s):  
Luke Collins ◽  
Adele Hunter ◽  
Sarah McColl-Gausden ◽  
Trent D. Penman ◽  
Philip Zylstra
Keyword(s):  
Seedling Recruitment ◽  
Fire Severity ◽  
Fire Weather ◽  
Canopy Layer ◽  
Eucalypt Forest ◽  
Crown Scorch ◽  
Eastern Australia ◽  
Eucalypt Forests ◽  
High Level

Research highlights—Feedbacks between fire severity, vegetation structure and ecosystem flammability are understudied in highly fire-tolerant forests that are dominated by epicormic resprouters. We examined the relationships between the severity of two overlapping fires in a resprouting eucalypt forest and the subsequent effect of fire severity on fuel structure. We found that the likelihood of a canopy fire was the highest in areas that had previously been exposed to a high level of canopy scorch or consumption. Fuel structure was sensitive to the time since the previous canopy fire, but not the number of canopy fires. Background and Objectives—Feedbacks between fire and vegetation may constrain or amplify the effect of climate change on future wildfire behaviour. Such feedbacks have been poorly studied in forests dominated by highly fire-tolerant epicormic resprouters. Here, we conducted a case study based on two overlapping fires within a eucalypt forest that was dominated by epicormic resprouters to examine (1) whether past wildfire severity affects future wildfire severity, and (2) how combinations of understorey fire and canopy fire within reburnt areas affect fuel properties. Materials and Methods—The study focused on ≈77,000 ha of forest in south-eastern Australia that was burnt by a wildfire in 2007 and reburnt in 2013. The study system was dominated by eucalyptus trees that can resprout epicormically following fires that substantially scorch or consume foliage in the canopy layer. We used satellite-derived mapping to assess whether the severity of the 2013 fire was affected by the severity of the 2007 fire. Five levels of fire severity were considered (lowest to highest): unburnt, low canopy scorch, moderate canopy scorch, high canopy scorch and canopy consumption. Field surveys were then used to assess whether combinations of understorey fire (<80% canopy scorch) and canopy fire (>90% canopy consumption) recorded over the 2007 and 2013 fires caused differences in fuel structure. Results—Reburn severity was influenced by antecedent fire severity under severe fire weather, with the likelihood of canopy-consuming fire increasing with increasing antecedent fire severity up to those classes causing a high degree of canopy disturbance (i.e., high canopy scorch or canopy consumption). The increased occurrence of canopy-consuming fire largely came at the expense of the moderate and high canopy scorch classes, suggesting that there was a shift from crown scorch to crown consumption. Antecedent fire severity had little effect on the severity patterns of the 2013 fire under nonsevere fire weather. Areas affected by canopy fire in 2007 and/or 2013 had greater vertical connectivity of fuels than sites that were reburnt by understorey fires, though we found no evidence that repeated canopy fires were having compounding effects on fuel structure. Conclusions—Our case study suggests that exposure to canopy-defoliating fires has the potential to increase the severity of subsequent fires in resprouting eucalypt forests in the short term. We propose that the increased vertical connectivity of fuels caused by resprouting and seedling recruitment were responsible for the elevated fire severity. The effect of antecedent fire severity on reburn severity will likely be constrained by a range of factors, such as fire weather.

Effects of trap position, trap history, microhabitat and season on capture probabilities of small mammals in a wet eucalypt forest

2005 ◽  
Vol 32 (8) ◽  
pp. 657 ◽  
Author(s):  
R. B. Cunningham ◽  
D. B. Lindenmayer ◽  
C. MacGregor ◽  
S. Barry ◽  
A. Welsh
Keyword(s):  
Small Mammals ◽  
Temporal Data ◽  
Binary Responses ◽  
Eucalypt Forest ◽  
Eastern Australia ◽  
History Of ◽  
Antechinus Agilis ◽  
Spatio Temporal ◽  
Eucalypt Forests ◽  
Trapping Grid

In this study, we use data drawn from a series of trapping events on four 0.5-ha trapping grids surveyed in the wet eucalypt forests of central Victoria, south-eastern Australia, to identify relationships between capture probabilities and several factors of interest for three species of small mammals that are common throughout the forests of this region: the agile antechinus (Antechinus agilis), the dusky antechinus (Antechinus swainsonii) and the bush rat (Rattus fuscipes). The design of our study – four regular trapping grids – generated spatio-temporal data with binary responses and many covariates. We used powerful and relatively new statistical methodology to deal with the spatio-temporal dependence patterns in the data – analytical problems that are common in trapping data such as these modelled here. Although A. agilis, A. swainsonii and R. fuscipes are among the best studied mammals in Australia, our data analysis produced new perspectives on their probability of being captured. In particular, we quantified how capture probability is affected by trap position within a trapping grid, day of capture in a sequence of trapping days, history of trap occupancy over time by different species and sexes of those species, time of the year or season, and microhabitat attributes. Our insights are discussed in terms of their consequences for trapping protocols that might be applied in the field.

Modelling the potential for prescribed burning to mitigate carbon emissions from wildfires in fire-prone forests of Australia

2012 ◽  
Vol 21 (6) ◽  
pp. 629 ◽  
Author(s):  
R. A. Bradstock ◽  
M. M. Boer ◽  
G. J. Cary ◽  
O. F. Price ◽  
R. J. Williams ◽  
...  
Keyword(s):  
Carbon Emissions ◽  
Prescribed Fire ◽  
Prescribed Burning ◽  
Fire Regimes ◽  
Fire Intensity ◽  
Eastern Australia ◽  
Burning Rates ◽  
Fuel Dynamics ◽  
Eucalypt Forests ◽  
In Fire

Prescribed fire can potentially reduce carbon emissions from unplanned fires. This potential will differ among ecosystems owing to inherent differences in the efficacy of prescribed burning in reducing unplanned fire activity (or ‘leverage’, i.e. the reduction in area of unplanned fire per unit area of prescribed fire). In temperate eucalypt forests, prescribed burning leverage is relatively low and potential for mitigation of carbon emissions from unplanned fires via prescribed fire is potentially limited. Simulations of fire regimes accounting for non-linear patterns of fuel dynamics for three fuel types characteristic of eucalypt forests in south-eastern Australia supported this prediction. Estimated mean annual fuel consumption increased with diminishing leverage and increasing rate of prescribed burning, even though average fire intensity (prescribed and unplanned fires combined) decreased. The results indicated that use of prescribed burning in these temperate forests is unlikely to yield a net reduction in carbon emissions. Future increases in burning rates under climate change may increase emissions and reduce carbon sequestration. A more detailed understanding of the efficacy of prescribed burning and dynamics of combustible biomass pools is required to clarify the potential for mitigation of carbon emissions in temperate eucalypt forests and other ecosystems.

Large herbivores suppress liana infestation in an African savanna

2021 ◽  
Vol 118 (41) ◽  
pp. e2101676118
Author(s):  
Tyler C. Coverdale ◽  
Ryan D. O’Connell ◽  
Matthew C. Hutchinson ◽  
Amanda Savagian ◽  
Tyler R. Kartzinel ◽  
...  
Keyword(s):  
Stable State ◽  
Life Forms ◽  
Tree Canopy ◽  
Alternative Stable State ◽  
African Savanna ◽  
Large Herbivore ◽  
Large Herbivores ◽  
Woody Vines ◽  
Plant Life Forms ◽  
Canopy Area

African savannas are the last stronghold of diverse large-mammal communities, and a major focus of savanna ecology is to understand how these animals affect the relative abundance of trees and grasses. However, savannas support diverse plant life-forms, and human-induced changes in large-herbivore assemblages—declining wildlife populations and their displacement by livestock—may cause unexpected shifts in plant community composition. We investigated how herbivory affects the prevalence of lianas (woody vines) and their impact on trees in an East African savanna. Although scarce (<2% of tree canopy area) and defended by toxic latex, the dominant liana, Cynanchum viminale (Apocynaceae), was eaten by 15 wild large-herbivore species and was consumed in bulk by native browsers during experimental cafeteria trials. In contrast, domesticated ungulates rarely ate lianas. When we experimentally excluded all large herbivores for periods of 8 to 17 y (simulating extirpation), liana abundance increased dramatically, with up to 75% of trees infested. Piecewise exclusion of different-sized herbivores revealed functional complementarity among size classes in suppressing lianas. Liana infestation reduced tree growth and reproduction, but herbivores quickly cleared lianas from trees after the removal of 18-y-old exclosure fences (simulating rewilding). A simple model of liana contagion showed that, without herbivores, the long-term equilibrium could be either endemic (liana–tree coexistence) or an all-liana alternative stable state. We conclude that ongoing declines of wild large-herbivore populations will disrupt the structure and functioning of many African savannas in ways that have received little attention and that may not be mitigated by replacing wildlife with livestock.

scholarly journals Path-dependent institutions drive alternative stable states in conservation

2018 ◽  
Vol 116 (2) ◽  
pp. 689-694 ◽  
Author(s):  
Edward W. Tekwa ◽  
Eli P. Fenichel ◽  
Simon A. Levin ◽  
Malin L. Pinsky
Keyword(s):  
Renewable Resources ◽  
Path Dependence ◽  
Alternative Stable States ◽  
Stable State ◽  
Empirical Support ◽  
Stable States ◽  
Alternative Stable State ◽  
Important Challenge ◽  
Quantitative Analyses ◽  
Path Dependent

Understanding why some renewable resources are overharvested while others are conserved remains an important challenge. Most explanations focus on institutional or ecological differences among resources. Here, we provide theoretical and empirical evidence that conservation and overharvest can be alternative stable states within the same exclusive-resource management system because of path-dependent processes, including slow institutional adaptation. Surprisingly, this theory predicts that the alternative states of strong conservation or overharvest are most likely for resources that were previously thought to be easily conserved under optimal management or even open access. Quantitative analyses of harvest rates from 217 intensely managed fisheries supports the predictions. Fisheries’ harvest rates also showed transient dynamics characteristic of path dependence, as well as convergence to the alternative stable state after unexpected transitions. This statistical evidence for path dependence differs from previous empirical support that was based largely on case studies, experiments, and distributional analyses. Alternative stable states in conservation appear likely outcomes for many cooperatively managed renewable resources, which implies that achieving conservation outcomes hinges on harnessing existing policy tools to navigate transitions.

scholarly journals Reproductive trajectories over decadal time-spans after fire for eight obligate-seeder shrub species in south-eastern Australia

2014 ◽  
Vol 62 (5) ◽  
pp. 369 ◽  
Author(s):  
Annette M. Muir ◽  
Peter A. Vesk ◽  
Graham Hepworth
Keyword(s):  
Seed Storage ◽  
Fire Frequency ◽  
Reproductive Maturity ◽  
South Eastern ◽  
Reproductive Response ◽  
Eastern Australia ◽  
Maturity Period ◽  
Fire Planning ◽  
In Fire ◽  
South Eastern Australia

Intervals between fires are critical for the persistence of obligate-seeding shrubs, and are often used in planning fires for fuel reduction and biodiversity conservation in fire-prone ecosystems worldwide. Yet information about the trajectories of reproductive performance for such species is limited and information is often qualitative. To test existing assumptions about reproductive maturity periods for eight obligate-seeding shrubs (with both canopy and soil seedbanks) in foothill forests of south-eastern Australia, we used a chronosequence approach, with sites from 2 years to >40 years post-fire. Quantitative measurements of flowering and fruiting were used to fit models of reproductive response in relation to time-since-fire for each species. Inferred reproductive maturity for each species, based on modelled times to reach 80% of maximum flower production, varied from 5 to 18 years post-fire. For a subset of three species, models predicted 80% maximum seed production occurring 1–7 years later than flowering. Our results confirmed or extended assumptions about post-fire reproductive maturity for these species, and provided a basis for improved incorporation of plant life-history in ecological fire planning. We infer that increased fire frequency makes one of our study taxa, Banksia spinulosa var. cunninghamii (Sieber ex Rchb.) A.S.George, vulnerable to decline because of its long reproductive maturity period and serotinous seed storage.

Uraba lugens (eucalypt leaf skeletonizer).

2021 ◽  
Author(s):  
Lisa Berndt
Keyword(s):  
New Zealand ◽  
Western Australia ◽  
Timber Production ◽  
Native Range ◽  
Natural Forests ◽  
Eastern Australia ◽  
Important Pest ◽  
Eucalypt Forests

Abstract U. lugens was first considered a serious pest of natural eucalypt forests in Western Australia in 1983 when the first severe outbreak occurred there (Strelein, 1988). Prior to that it was widely known as a pest of eucalypt forests in eastern Australia (Campbell, 1962; Harris, 1974). As these natural forests are or were managed for timber production, it is considered an economically important pest in its native range. Damage to amenity trees is also a common problem, although few trees are killed by this defoliation (Anonymous, 1979).U. lugens was recorded as invasive in New Zealand by Crabtree (1997). In its exotic range it has become a significant pest of amenity trees, particularly Lophestemon confertus (Australian brush box), which is commonly planted in some parts of Auckland City (Kriticos et al., 2007).

Uncertain ecosystems: the conceptual framework

2019 ◽  
pp. 27-42
Author(s):  
William J. Bond
Keyword(s):  
Trophic Ecology ◽  
Resource Constraints ◽  
Stable State ◽  
State Theory ◽  
Tree Cover ◽  
Top Down ◽  
Alternative Stable State ◽  
Positive Feedbacks ◽  
Vegetation Models ◽  
Global Vegetation

Climate sets the potential biomass of trees and physiologists have made considerable progress in understanding and predicting that potential and applying it in global vegetation models. The problem is in understanding and predicting tree cover where it is far from the climate potential. Vast areas of non-forested vegetation occur where climates are suitable for forests. Arguments over why forests are absent, ongoing for over a century, are generally polarized between favouring bottom-up factors (resource constraints) or top-down factors (herbivory, predation, fire). There is increasing support for hypotheses invoking the interaction between the two. This chapter introduces the key hypotheses, their assumptions and predictions. Trophic ecology is a useful framework for exploring departures from the climate potential for trees, focussing explicitly on regulation by consumers, including fire. Alternative stable state theory is emerging as particularly appropriate for explaining forest/non-forest mosaics with each state maintained by positive feedbacks to the preferred environment.

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