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Differential demographic filtering by surface fires: How fuel type and fuel load affect sapling mortality of an obligate seeder savanna tree

Bowman, DMJS ORCID: 0000-0003-2215-7685, Haverkamp, C, Rann, KD and Prior, LD ORCID: 0000-0002-5511-2320 2017 , 'Differential demographic filtering by surface fires: How fuel type and fuel load affect sapling mortality of an obligate seeder savanna tree' , Journal of Ecology, vol. 106, no. 3 , pp. 1010-1022 , doi: 10.1111/1365-2745.12819.

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Abstract

We studied the effects of fuel type, fuel load and their associated flammability attributes on growth and survival of Callitris intratropica saplings. Callitris intratropica is a fire-sensitive conifer that is widespread across northern Australia, but its range is contracting because of frequent and intense fires.A small-scale field experiment was used to compare the effect of three fuel types (grass, eucalypt litter and C. intratropica litter), and a mix of grass and eucalypt litter by varying fuel loads within their naturally occurring bounds, and measuring multiple flammability attributes.Fuel type had the strongest influence on flammability attributes and hence sapling survival. Grass burnt rapidly, producing high temperatures, while duration of flaming was longer for eucalypt litter. Grass–eucalypt litter mixtures had flammability attributes more like grass, while C. intratropica litter was difficult to burn. Fuel load had a secondary effect, with strong interactions between fuel type and load.Differences in sapling survival could be attributed to temperatures at 5 cm height; there was no additional effect of fuel type or canopy temperature. Sapling size variables were also important, and strongly correlated with bark thickness, so we could not identify the protective mechanism.Synthesis. Mortality of Callitris intratropica saplings was consistent with damage to the lower stem, because of the direct relationship with temperatures at 5 cm height. Our results demonstrate the existence of a grass–fire cycle in C. intratropica stands, whereby hot fires damage the stands and allow grass to invade, increasing the stand ignitability and combustibility and promoting further fires. Interrupting this cycle by reducing grass fuel loads and hence the frequency of hot fires should therefore be a management priority to safeguard C. intratropica populations. Our findings also highlight that, under a common climate, vegetation type can shape fire regimes, because fuel type strongly influences flammability attributes, which in turn act as a powerful filter of plant populations.

Item Type: Article
Authors/Creators:Bowman, DMJS and Haverkamp, C and Rann, KD and Prior, LD
Keywords: bark thickness, conifer, fire, fuels, flammability, mortality, Callitris intratropica, determinants of plant community diversity and structure, fire regime, grass fuels, lethal temperature, litter fuels, tropical savanna
Journal or Publication Title: Journal of Ecology
Publisher: Blackwell Publishing Ltd
ISSN: 0022-0477
DOI / ID Number: 10.1111/1365-2745.12819
Copyright Information:

© 2017 The Authors

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