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      Determinants of flammability in savanna grass species

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          Summary

          1. Tropical grasses fuel the majority of fires on Earth. In fire‐prone landscapes, enhanced flammability may be adaptive for grasses via the maintenance of an open canopy and an increase in spatiotemporal opportunities for recruitment and regeneration. In addition, by burning intensely but briefly, high flammability may protect resprouting buds from lethal temperatures. Despite these potential benefits of high flammability to fire‐prone grasses, variation in flammability among grass species, and how trait differences underpin this variation, remains unknown.

          2. By burning leaves and plant parts, we experimentally determined how five plant traits (biomass quantity, biomass density, biomass moisture content, leaf surface‐area‐to‐volume ratio and leaf effective heat of combustion) combined to determine the three components of flammability (ignitability, sustainability and combustibility) at the leaf and plant scales in 25 grass species of fire‐prone South African grasslands at a time of peak fire occurrence. The influence of evolutionary history on flammability was assessed based on a phylogeny built here for the study species.

          3. Grass species differed significantly in all components of flammability. Accounting for evolutionary history helped to explain patterns in leaf‐scale combustibility and sustainability. The five measured plant traits predicted components of flammability, particularly leaf ignitability and plant combustibility in which 70% and 58% of variation, respectively, could be explained by a combination of the traits. Total above‐ground biomass was a key driver of combustibility and sustainability with high biomass species burning more intensely and for longer, and producing the highest predicted fire spread rates. Moisture content was the main influence on ignitability, where species with higher moisture contents took longer to ignite and once alight burnt at a slower rate. Biomass density, leaf surface‐area‐to‐volume ratio and leaf effective heat of combustion were weaker predictors of flammability components.

          4. Synthesis. We demonstrate that grass flammability is predicted from easily measurable plant functional traits and is influenced by evolutionary history with some components showing phylogenetic signal. Grasses are not homogenous fuels to fire. Rather, species differ in functional traits that in turn demonstrably influence flammability. This diversity is consistent with the idea that flammability may be an adaptive trait for grasses of fire‐prone ecosystems.

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          Phylogenetic analysis of community assembly and structure over space and time.

          Evolutionary ecologists are increasingly combining phylogenetic data with distributional and ecological data to assess how and why communities of species differ from random expectations for evolutionary and ecological relatedness. Of particular interest have been the roles of environmental filtering and competitive interactions, or alternatively neutral effects, in dictating community composition. Our goal is to place current research within a dynamic framework, specifically using recent phylogenetic studies from insular environments to provide an explicit spatial and temporal context. We compare communities over a range of evolutionary, ecological and geographic scales that differ in the extent to which speciation and adaptation contribute to community assembly and structure. This perspective allows insights into the processes that can generate community structure, as well as the evolutionary dynamics of community assembly.
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            Defining pyromes and global syndromes of fire regimes

            Fire is a ubiquitous component of the Earth system that is poorly understood. To date, a global-scale understanding of fire is largely limited to the annual extent of burning as detected by satellites. This is problematic because fire is multidimensional, and focus on a single metric belies its complexity and importance within the Earth system. To address this, we identified five key characteristics of fire regimes--size, frequency, intensity, season, and extent--and combined new and existing global datasets to represent each. We assessed how these global fire regime characteristics are related to patterns of climate, vegetation (biomes), and human activity. Cross-correlations demonstrate that only certain combinations of fire characteristics are possible, reflecting fundamental constraints in the types of fire regimes that can exist. A Bayesian clustering algorithm identified five global syndromes of fire regimes, or pyromes. Four pyromes represent distinctions between crown, litter, and grass-fueled fires, and the relationship of these to biomes and climate are not deterministic. Pyromes were partially discriminated on the basis of available moisture and rainfall seasonality. Human impacts also affected pyromes and are globally apparent as the driver of a fifth and unique pyrome that represents human-engineered modifications to fire characteristics. Differing biomes and climates may be represented within the same pyrome, implying that pathways of change in future fire regimes in response to changes in climate and human activity may be difficult to predict.
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              Evolutionary ecology of resprouting and seeding in fire-prone ecosystems.

              There are two broad mechanisms by which plant populations persist under recurrent disturbances: resprouting from surviving tissues, and seedling recruitment. Species can have one of these mechanisms or both. However, a coherent framework explaining the differential evolutionary pressures driving these regeneration mechanisms is lacking. We propose a bottom-up approach in addressing this question that considers the relative survivorship of adults and juveniles in an evolutionary context, based on two assumptions. First, resprouting and seeding can be interpreted by analogy with annual versus perennial life histories; that is, if we consider disturbance cycles to be analogous to annual cycles, then resprouting species are analogous to the perennial life history with iteroparous reproduction, and obligate seeding species that survive disturbances solely through seed banks are analogous to the annual life history with semelparous reproduction. Secondly, changes in the selective regimes differentially modify the survival rates of adults and juveniles and thus the relative costs and benefits of resprouting versus seeding. Our approach provides a framework for understanding temporal and spatial variation in resprouting and seeding under crown-fire regimes. It accounts for patterns of coexistence and environmental changes that contribute to the evolution of seeding from resprouting ancestors.
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                Author and article information

                Journal
                J Ecol
                J. Ecol
                10.1111/(ISSN)1365-2745
                JEC
                The Journal of Ecology
                John Wiley and Sons Inc. (Hoboken )
                0022-0477
                1365-2745
                26 November 2015
                January 2016
                : 104
                : 1 ( doiID: 10.1111/jec.2016.104.issue-1 )
                : 138-148
                Affiliations
                [ 1 ] Department of Animal and Plant SciencesUniversity of Sheffield Sheffield S10 2TNUK
                [ 2 ] Department of BotanyRhodes University PO Box 94 Grahamstown 6140South Africa
                [ 3 ] College of Life and Environmental SciencesUniversity of Exeter Exeter EX4 4PSUK
                [ 4 ] School of GeoSciencesUniversity of Edinburgh Edinburgh EH9 3JNUK
                Author notes
                [*] [* ]Correspondence author: E‐mail: c.p.osborne@ 123456shef.ac.uk
                Article
                JEC12503
                10.1111/1365-2745.12503
                4738432
                26877549
                48d525a4-0829-449a-90e5-dec41c3ab2ef
                © 2015 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 19 March 2015
                : 26 October 2015
                Page count
                Pages: 11
                Funding
                Funded by: Natural Environment Research Council
                Funded by: Royal Society University Research Fellowship
                Award ID: URF120119
                Award ID: URF120016
                Funded by: European Research Council
                Award ID: ERC‐2013‐StG‐335891‐ECOFLAM
                Categories
                Standard Paper
                Determinants of Plant Community Diversity and Structure
                Custom metadata
                2.0
                jec12503
                January 2016
                Converter:WILEY_ML3GV2_TO_NLMPMC version:4.7.5 mode:remove_FC converted:28.01.2016

                Ecology
                biomass moisture content,biomass quantity,determinants of plant community diversity and structure,fire regime,functional traits,phylogeny,poaceae,resprouting

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