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

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.

Phylogenomics shows lignotuber state is taxonomically informative in closely related eucalypts.

Plant taxa can be broadly divided based on the mechanisms enabling persistence through whole-crown disturbances, specifically whether individuals resprout, populations reseed, or both or neither of these mechanisms are employed. At scales from species through to communities, the balance of disturbance-response types has major ramifications for ecological function and biodiversity conservation. In some lineages, morphologically identical populations except for differences in a disturbance-response trait (e.g. ±â€¯lignotuber) occur, offering the opportunity to apply genetic analyses to test whether trait state is representative of broader genetic distinctiveness, or alternatively, variation in response to local environmental conditions. In eucalypts, a globally-significant plant group, we apply dense taxon sampling and high-density, genome-wide markers to test monophyly and genetic divergence among pairs of essentially morphologically-identical taxa excepting lignotuber state. Taxa differing in lignotuber state formed discrete phylogenetic lineages. Obligate-seeders were monophyletic and strongly differentiated from each other and lignotuber-resprouters, but this was not the case for all lignotuber-resprouter taxa. One lignotuber state transition within our sample clade was supported, implying convergence of some non-lignotuber morphology characters. Greater evolutionary rate associated with the obligate-seeder disturbance-response strategy offers a plausible explanation for these genetic patterns. Lignotuber state is an important taxonomic character in eucalypts, with transitions in lignotuber state having contributed to the evolution of the exceptional diversity of eucalypts in south-western Australia. Differences in lignotuber state have evolved directionally with respect to environmental conditions.

Fire management strategies to maintain species population processes in a fragmented landscape of fire-interval extremes.

Changed fire regimes have led to declines of fire-regime-adapted species and loss of biodiversity globally. Fire affects population processes of growth, reproduction, and dispersal in different ways, but there is little guidance about the best fire regime(s) to maintain species population processes in fire-prone ecosystems. We use a process-based approach to determine the best range of fire intervals for keystone plant species in a highly modified Mediterranean ecosystem in southwestern Australia where current fire regimes vary. In highly fragmented areas, fires are few due to limited ignitions and active suppression of wildfire on private land, while in highly connected protected areas fires are frequent and extensive. Using matrix population models, we predict population growth of seven Banksia species under different environmental conditions and patch connectivity, and evaluate the sensitivity of species survival to different fire management strategies and burning intervals. We discover that contrasting, complementary patterns of species life-histories with time since fire result in no single best fire regime. All strategies result in the local patch extinction of at least one species. A small number of burning strategies secure complementary species sets depending on connectivity and post-fire growing conditions. A strategy of no fire always leads to fewer species persisting than prescribed fire or random wildfire, while too-frequent or too-rare burning regimes lead to the possible local extinction of all species. In low landscape connectivity, we find a smaller range of suitable fire intervals, and strategies of prescribed or random burning result in a lower number of species with positive growth rates after 100 years on average compared with burning high connectivity patches. Prescribed fire may reduce or increase extinction risk when applied in combination with wildfire depending on patch connectivity. Poor growing conditions result in a significantly reduced number of species exhibiting positive growth rates after 100 years of management. By exploring the consequences of managing fire, we are able to identify which species are likely to disappear under a given fire regime. Identifying the appropriate complementarity of fire intervals, and their species-specific as well as community-level consequences, is crucial to reduce local extinctions of species in fragmented fire-prone landscapes.

A synthesis of postfire recovery traits of woody plants in Australian ecosystems.

Postfire resprouting and recruitment from seed are key plant life-history traits that influence population dynamics, community composition and ecosystem function. Species can have one or both of these mechanisms. They confer resilience, which may determine community composition through differential species persistence after fire. To predict ecosystem level responses to changes in climate and fire conditions, we examined the proportions of these plant fire-adaptive traits among woody growth forms of 2880 taxa, in eight fire-prone ecosystems comprising ~87% of Australia's land area. Shrubs comprised 64% of the taxa. More tree (>84%) than shrub (~50%) taxa resprouted. Basal, epicormic and apical resprouting occurred in 71%, 22% and 3% of the taxa, respectively. Most rainforest taxa (91%) were basal resprouters. Many trees (59%) in frequently-burnt eucalypt forest and savanna resprouted epicormically. Although crown fire killed many mallee (62%) and heathland (48%) taxa, fire-cued seeding was common in these systems. Postfire seeding was uncommon in rainforest and in arid Acacia communities that burnt infrequently at low intensity. Resprouting was positively associated with ecosystem productivity, but resprouting type (e.g. basal or epicormic) was associated with local scale fire activity, especially fire frequency. Although rainforest trees can resprout they cannot recruit after intense fires and may decline under future fires. Semi-arid Acacia communities would be susceptible to increasing fire frequencies because they contain few postfire seeders. Ecosystems dominated by obligate seeders (mallee, heath) are also susceptible because predicted shorter inter-fire intervals will prevent seed bank accumulation. Savanna may be resilient to future fires because of the adaptive advantage of epicormic resprouting among the eucalypts. The substantial non-resprouting shrub component of shrublands may decline, but resilient Eucalyptus spp. will continue to dominate under future fire regimes. These patterns of resprouting and postfire seeding provide new insights to ecosystem assembly, resilience and vulnerability to changing fire regimes on this fire-prone continent.

Estimating fire interval bounds using vital attributes: implications of uncertainty and among-population variability.

Identifying the range of appropriate fire return intervals is crucial for ecosystem management in fire-prone environments. Plant vital attributes and changes in their associated trait values with time since fire are important indicators of suitable fire interval bounds to conserve biodiversity. However, using vital attributes to derive prescriptions for acceptable fire intervals remains challenging due to (1) uncertainty regarding how traits are best measured, (2) uncertainty in the acceptable ranges of trait values to avoid local extinctions, and (3) potential for variability among populations in the time taken postfire to reach trait threshold values. Using a time-since-fire gradient in contrasting mallee and mallee-heath vegetation types of southwestern Australia, we calculate, compare, and aggregate fire interval bound predictions from nine serotinous non-resprouters and seven serotinous resprouters across these three sources of uncertainty or variation. Relationships between time since fire and both trait measures reflecting minimum fire interval (mean number of closed fruit per plant or proportion of plants with closed fruit) were typically significant, had reasonable goodness of fit, and showed similar patterns of change with time since fire. Significant relationships reflecting maximum fire interval were less frequent but were more commonly detected using direct measures of mortality than using evidence for decline in reproductive potential. Of the two sources of uncertainty, trait value threshold selection caused more substantial differences in estimated interval bounds than trait measurement method. Variation between populations increased with greater estimated minimum interval length and, in some species, rendered interval estimates of limited practical value. On balance, we conclude that measures of vital attribute traits offer a transparent approach for estimating fire interval bounds at the plant community level, but selection of trait value thresholds is in need of stronger biological justification in their application. Further, variation between populations should be explicitly sampled if fire interval estimates are to be applied across the landscape.