Where fire stops: vegetation structure and microclimate influence fire spread along an ecotonal gradient

Just, Michael G.; Hohmann, Matthew G.; Hoffmann, William A.

doi:10.1007/s11258-015-0545-x

Cited by 46 publications

(24 citation statements)

References 61 publications

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“…In fact, previous work in longleaf pine savannas has documented increases in microbial biomass following fire (Wilson et al, 2002). In contrast to the microbial community, prescribed burns in our study system generally top-kill a majority of the aboveground herbaceous and woody biomass with stem diameters less than 10 cm (Just et al, 2016). If fire damage temporarily halted or slowed the plant uptake of inorganic N, we would expect to see an accumulation of soil N if microbial immobilization did not increase sufficiently to deplete the pool.…”

Section: Assessing Mechanisms Of N Pulses Following Firecontrasting

confidence: 49%

Contributions of microbial activity and ash deposition to post-fire nitrogen availability in a pine savanna

Ficken

Wright

2017

Biogeosciences

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Abstract. Many ecosystems experience drastic changes to soil nutrient availability associated with fire, but the magnitude and duration of these changes are highly variable among vegetation and fire types. In pyrogenic pine savannas across the southeastern United States, pulses of soil inorganic nitrogen (N) occur in tandem with ecosystem-scale nutrient losses from prescribed burns. Despite the importance of this management tool for restoring and maintaining fire-dependent plant communities, the contributions of different mechanisms underlying fire-associated changes to soil N availability remain unclear. Pulses of N availability following fire have been hypothesized to occur through (1) changes to microbial cycling rates and (2) direct ash deposition. Here, we document fire-associated changes to N availability across the growing season in a longleaf pine savanna in North Carolina. To differentiate between possible mechanisms driving soil N pulses, we measured net microbial cycling rates and changes to soil δ 15 N before and after a burn. Our findings refute both proposed mechanisms: we found no evidence for changes in microbial activity, and limited evidence that ash deposition could account for the increase in ammonium availability to more than 5-25 times background levels. Consequently, we propose a third mechanism to explain post-fire patterns of soil N availability, namely that (3) changes to plant sink strength may contribute to ephemeral increases in soil N availability, and encourage future studies to explicitly test this mechanism.

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Section: Assessing Mechanisms Of N Pulses Following Firecontrasting

confidence: 49%

Contributions of microbial activity and ash deposition to post-fire nitrogen availability in a pine savanna

Ficken

Wright

2017

Biogeosciences

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“…Contrasting fire regimes are considered key factors influencing these vegetation types and maintaining sharp boundaries between the two (Dantas, Hirota, Oliveira, & Pausas, ). Rain forests are rarely burnt, because the dense canopy cover creates a moist microclimate and little flammable grass is present (Little, Williams, Prior, Williamson, & Bowman, ), limiting the incursion of fire (Just, Hohmann, & Hoffmann, ). When fires do occur, they are typically mild surface fires in leaf litter (Cochrane, ).…”

Section: Introductionmentioning

confidence: 99%

Fire and cattle disturbance affects vegetation structure and rain forest expansion into savanna in the Australian monsoon tropics

Ondei

Prior

Vigilante

et al. 2017

Journal of Biogeography

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Aims: To detect changes in area and vegetation dynamics of monsoon rain forests in relation to disturbance and an observed wetting trend. Location: The Mitchell Plateau and the Bougainville Peninsula (north Kimberley, Australia). Methods: Geo-rectified aerial photographs acquired in 1949 and 1969 and a preexisting map from 2005 were used to detect changes in rain forest boundaries. To ground-truth rain forest expansion, we established 20 transects running across rain forest-savanna boundaries and recorded plant species, stand basal area, grass and rock cover, cattle impact, and canopy cover. Generalised linear models and Akaike's information criterion were used to detect differences in these variables between locations. Results: On the Bougainville Peninsula average fire frequency was low (0.11 per year) and cattle entirely absent, while on the Mitchell Plateau average fire frequency was high (0.58 per year), and cattle were common and associated with lower seedling density in savannas. Rain forests expanded more on the Bougainville Peninsula (69%),where patches were bigger and more convoluted, than on the Mitchell Plateau (9%).Rain forest expansion was positively associated with rainfall and topographic complexity, and on level terrain it occurred only on the Bougainville Peninsula. Rain forests were floristically and structurally similar in the two locations, while savannas on the Bougainville Peninsula had denser vegetation and more abundant rain forest elements.The frequency distribution of canopy cover was bimodal on the Mitchell Plateau, signalling the presence of two distinct vegetation states, and unimodal on the Bougainville Peninsula, consistent with the blending of the two states.Main conclusions: Wetting trends are likely strong drivers of rain forest expansion, but at a landscape scale their effect is probably modulated by fire activity and the presence of mega-herbivores, which may also be pivotal in maintaining sharp floristic and structural distinctions between rain forests and savannas. K E Y W O R D SAustralian tropics, cattle impact, climate change, fire, historical aerial photography, monsoon rain forests, tropical savannas

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“…This allows experimental fires to burn under more uniform conditions than is possible in most other regions. In addition, these savannas contain vegetation types that produce surface fuels with sharply contrasting flammability attributes (Bowman & Wilson, ), namely (1) very well‐aerated, tall tropical grass fuels, which burn rapidly (Bowman, French, et al., ; Bowman, MacDermott, et al., ; Just, Hohmann, & Hoffmann, ); (2) eucalypt litter fuels, which burn more slowly and less completely than grass fuels (Hollis, Gould, Cruz, & McCaw, ; Prior et al., ); and (3) dense mats of conifer litter beneath stands of C. intratropica , which are difficult to ignite and burn incompletely (Trauernicht et al., ). We therefore used this ecosystem to conduct a field experiment to measure flammability attributes of these three contrasting fine fuel types, as well as mixes of grass and eucalypt litter.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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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.

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Where fire stops: vegetation structure and microclimate influence fire spread along an ecotonal gradient

Cited by 46 publications

References 61 publications

Contributions of microbial activity and ash deposition to post-fire nitrogen availability in a pine savanna

Contributions of microbial activity and ash deposition to post-fire nitrogen availability in a pine savanna

Fire and cattle disturbance affects vegetation structure and rain forest expansion into savanna in the Australian monsoon tropics

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

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