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    Assessing the sensitivity of biodiversity indices used to inform fire management
    Giljohann, KM ; Kelly, LT ; Connell, J ; Clarke, MF ; Clarke, RH ; Regan, TJ ; McCarthy, MA ; Blanchard, J (WILEY, 2018-03)
    Biodiversity indices are widely used to summarize changes in the distribution and abundance of multiple species and measure progress towards management targets. However, the sensitivity of biodiversity indices to the data, landscape classification and conservation values underpinning them are rarely interrogated. There are limited studies to help scientists and land managers use biodiversity indices in the presence of fire and vegetation succession. The geometric mean of species' relative abundance or occurrence (G) is a biodiversity index that can be used to determine the mix of post‐fire vegetation that maximizes biodiversity. We explored the sensitivity of G to (1) type of biodiversity data, (2) representation of ecosystem states, (3) expression of conservation values, and (4) uncertainty in species' response to landscape structure. Our case study is an area of fire‐prone woodland in southern Australia where G is used in fire management planning. We analysed three datasets to determine the fire responses of 170 bird, mammal and reptile species. G and fire management targets were sensitive to the species included in the analysis. The optimal mix of vegetation successional states for threatened birds was more narrowly defined than the optimal mix for all species combined. G was less sensitive to successional classification (i.e. number of states); although classifications of increasing complexity provided additional insights into desirable levels of heterogeneity. Weighting species by conservation status or endemism influenced the mix of vegetation states that maximized biodiversity. When a higher value was placed on threatened species the importance of late successional vegetation was emphasized. Representing variation in individual species' response to vegetation structure made it clearer when a decrease in G was likely to reflect a significant reduction in species occurrences. Synthesis and applications. Data, models and conservation values can be combined using biodiversity indices to make robust environmental decisions. Combining different types of biodiversity data using composite indices, such as the geometric mean, can improve the coverage and relevance of biodiversity indices. We recommend that evaluation of biodiversity indices for fire management verify how index assumptions align with management objectives, consider the relative merits of different types of biodiversity data, test sensitivity of ecosystem state definitions and incorporate conservation values through species weightings.
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    Interactions between rainfall, fire and herbivory drive resprouter vital rates in a semi-arid ecosystem
    Giljohann, KM ; McCarthy, MA ; Keith, DA ; Kelly, LT ; Tozer, MG ; Regan, TJ ; Salguero‐Gómez, R (WILEY, 2017-11)
    Summary Global change is threatening ecosystems and biodiversity world‐wide, creating a pressing need to understand how climate and disturbance regimes interact and influence the persistence of species. We quantify how three ecosystem drivers – rainfall, fire and herbivory – influence vital rates in the perennial resprouting graminoid, Triodia scariosa, a foundation species of semi‐arid Australia. We used an 11‐year dataset from a fire and herbivore exclosure experiment, to model flowering, post‐fire recruitment and the post‐fire survival of seedlings and resprouting plants. Regression modelling quantified the effect of rainfall, inter‐fire interval, fire type (wildfire or prescribed fire), grazing by herbivores (native and feral) and an interaction between fire type and herbivory on T. scariosa populations. Rainfall, fire and herbivory had significant effects on post‐fire recruitment and the survival of seedlings and resprouting plants, including strong interactions between these drivers. Herbivory following wildfire had a minor effect, but in years of below‐average rainfall herbivory following prescribed fire had a large effect, reducing the survival of seedlings and resprouting plants by 20% and over 50% respectively, relative to post‐fire survival under average rainfall conditions. Variation in rainfall underpinned significant variation in post‐fire resprouting and seedling survival, thus we postulate rainfall primarily drives the dynamics of T. scariosa populations. Synthesis. This study highlights the importance of modelling interactions between key ecosystem drivers when predicting how changes in global climate and disturbance regimes influence plant vital rates. Relatively small changes to disturbance regimes can substantially alter population processes, even in perennial resprouting species. This work suggests that conservation of foundation species, such as T. scariosa, will benefit if fire management decisions are better integrated with inter‐annual weather forecasts and herbivore management.