Reconstructing the spread of landscape-scale fires in semi-arid southwestern Australia

Ecological Applications

Watson

Fox

et al. 2019

In an era characterized by recurrent large wildfires in many parts of the globe, there is a critical need to understand how animal species respond to fires, the rates at which populations can recover, and the functional changes fires may cause. Using quantified changes in habitat parameters over a~400-yr post-fire chronosequence in an obligate-seeding Australian eucalypt woodland, we build and test predictions of how birds, as individual species and aggregated into functional groups according to their use of specific habitat resources, respond to time since fire. Individual bird species exhibited four generalized response types to time since fire: incline, decline, delayed, and bell. All significant relationships between bird functional group richness or abundance and time since fire were consistent with predictions based on known time-since-fire-associated changes in habitat features putatively important for these bird groups. Consequently, we argue that the bird community is responding to post-fire successional changes in habitat as per the habitat accommodation model, rather than to time since fire per se, and that our functional framework will be of value in predicting bird responses to future disturbances in this and other obligate-seeder forest and woodland ecosystems. Most bird species and functional groups that were affected by time since fire were associated with long-unburned woodlands. In the context of recent large, stand-replacement wildfires that have affected a substantial proportion of obligate-seeder eucalypt woodlands, and the multi-century timescales over which post-fire succession occurs, it would appear preferable from a bird conservation perspective if fires initiating loss of currently long-unburned woodlands were minimized. Once long-unburned woodlands are transformed by fire into recently burned woodlands, there is limited scope for alternative management interventions to accelerate the rate of habitat development after fire, or supplement the resources formerly provided to birds by long-unburned woodlands, with the limited exception of augmenting hollow availability for key hollow-nesting species.

Section: Discussionmentioning

confidence: 99%

Section: Management Of Resources Provided By Long-unburned Woodlandsmentioning

confidence: 99%

Fire‐mediated habitat change regulates woodland bird species and functional group occurrence

Ecological Applications

Watson

Fox

et al. 2019

“…There can be wide variation in the scale at which stand‐replacement disturbances occur, ranging from a few hectares in lightning‐ignited fires extinguished after a few hours by rain, through to tens of thousands of hectares burnt by a large fire run on a single day under severe weather conditions (McCaw et al . ). With disturbance‐induced mortality of mature trees, below‐ground competition for water is temporarily removed (Yates et al .…”

Section: Transitions Between Statesmentioning

confidence: 97%

“…Multiple large (>100 000 ha; McCaw et al . ) wildfires are of particular concern and in recent decades have cumulatively burnt a significant proportion of total woodland area (Fig. c), for example >20% of woodlands in the western half of the GWW since ~1970 (Gosper et al .…”

Section: Introductionmentioning

confidence: 99%

A conceptual model of vegetation dynamics for the unique obligate‐seeder eucalypt woodlands of south‐western Australia

Yates²,

Cook

et al. 2018

Austral Ecology

Models of vegetation dynamics framed as testable hypotheses provide powerful tools for predicting vegetation change in response to contemporary disturbances or climate change. Synthesizing existing information and applying new data, we develop a conceptual model of vegetation states and transitions for the previously overlooked woodlands dominated by obligate-seeder eucalypts of dry to semi-arid south-western Australia. These comprise the largest extant temperate woodland globally, are uniquely dominated by a high diversity of obligateseeder eucalypts (55 taxa), but are under threat from wildfire. Our conceptual model incorporates four critical ecological processes that also distinguish obligate-seeder woodlands from temperate woodlands dominated by resprouting eucalypts: (i) a lack of well-protected epicormic buds results in major disturbances (prominently fire) being stand-replacing. The pre-disturbance tree cohort is killed, followed by dense post-disturbance recruitment from seed shed from a serotinous seed bank; (ii) competition between saplings leads to self-thinning over a multi-century timeframe, with surviving individuals having great longevity (regularly >400 years); (iii) multiple processes limit recruitment in the absence of stand-replacement disturbances, leading to frequent single-cohort stands. However, unlike the few other obligate-seeder eucalypt communities, trickle recruitment in very longunburnt stands can facilitate indefinite community persistence in the absence of stand-replacement disturbances; and (iv) discontinuous fuels, relatively low understorey flammability (low grass and often high chenopod cover) and topographic barriers to fire (salt lakes) allow mature woodlands to persist for centuries without burning. Notably though, evidence suggests that flammability peaks at intermediate times since fire, establishing a 'flammability bottleneck' (or landscape fire trap) through which regenerating woodlands must pass. Our model provides a framework to support management to conserve obligate-seeder eucalypt woodlands. Research into reasons for exceptional tree heights relative to ecosystem productivity, the evolution of diverse and dominant obligate-seeder eucalypts, the paucity of grass, and the recent spatial distribution of fires, will further inform conservation management.

“…This spatial pattern of occurrence raises the prospect that colonisation was initially facilitated by proximity to the fire edge (and presumably extant individuals, although we have no data on distance to extant individuals), perhaps due to short-distance seed dispersal [14]. Either dispersal (associated with often large fire size combined with disperser behaviour [14][15][16]) or recruitment (associated with changes in post-fire obligate-seeder host stature and community structure in regenerating woodlands [9,17]) limitations are plausible in explaining mistletoe absence from young and most intermediate-aged woodlands. If recruitment opportunities are the limiting factor, then post-fire mistletoe recolonisation, even after a crown fire, may be much more rapid in ecosystems dominated by epicormically-resprouting hosts.…”

mentioning

confidence: 93%

Using a Multi-Century Post-Fire Chronosequence to Develop Criteria to Distinguish Prior and Bowman’s (2020) Post-Fire Obligate Coloniser and Fire-Intolerant Flora

Prober

2020

Fire

Prior and Bowman added a new dimension to existing frameworks of post-fire responses of woody plants, by including the trait of colonisation ability (C) for those taxa which neither resprout (Rf−) nor produce seedlings (Sf−) after fire. Specifically, they recognised distinctions between: (i) post-fire obligate colonisers, being species that neither resprout nor produce seedlings from persistent seed banks post-fire but are able to colonise burnt areas through dispersal from unburnt populations, and (ii) fire-intolerant, which are unable to recover after fire by either resprouting, seeding or colonisation. We use data on temporal and spatial patterns of colonisation of Rf−Sf− mistletoes from a chronosequence study with an exceptionally long span of times since fire as a practical example of the delineation of post-fire obligate coloniser and fire-intolerant species. We propose that when a population of a species is burnt, if the species is unable to regularly colonise and reach reproductive maturity in burnt areas spatially distant from fire edges within plausible and regularly-occurring maximum fire-return intervals for the now-burnt community type, it would be classified as fire-intolerant. In our examples, Lysiana meets the criteria for fire-intolerant in obligate-seeder eucalypt woodland, while Amyema is classed as a post-fire obligate coloniser.