Response of vegetation and vertebrate fauna to 23 years of fire exclusion in a tropical Eucalyptus open forest. Northern Territory, Australia

Woinarski, J. C. Z.; Risler, J.; Kean, Louise

doi:10.1111/j.1442-9993.2004.tb00308.x

Cited by 85 publications

(169 citation statements)

References 44 publications

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“…Rossatto et al (2009) found that forest species grew (diameter growth) faster than did savanna species in cerrado, but their fire response ) suggests that forest species did not acquire thicker bark than savanna species. Similarly, although in Australia forest species grow faster than savanna species (Prior et al 2004) they are excluded from savannas by fire impacts (Wilson and Bowman 1994, Russell-Smith et al 2003, Woinarski et al 2004). More importantly in our study of a typical fire-prone Australian savanna, height-response or fast height growth per se did not explain the success of the eucalypts; by simply growing taller than the flame height, trees did not necessarily escape the effects of fire (cf.…”

Section: Discussionmentioning

confidence: 99%

How do small savanna trees avoid stem mortality by fire? The roles of stem diameter, height and bark thickness

et al. 2011

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Abstract. To recruit to reproductive size in fire-prone savannas, juvenile trees must avoid stem mortality (topkill) by fire. Theory suggests they either grow tall, raising apical buds above the flames, or wide, buffering the stem from fire. However, growing tall or wide is of no advantage without stem protection from fire. In Litchfield National Park, northern Australia, we explored the importance of bark thickness to stem survival following fire in a eucalypt-dominated tropical savanna. We measured bark thickness, prefire height, stem diameter and resprouting responses of small stems under conditions of low to moderate fire intensity. Fire induced mortality was low (,10%), topkill was uncommon (,11% of 5 m to 37% of 1 m tall stems) and epicormic resprouting was common. Topkill was correlated only with absolute bark thickness and not with stem height or width. Thus, observed height and diameter growth responses of small stems are likely different pathways to achieving bark thick enough to protect buds and the vascular cambium. Juvenile height was traded off against the cost of thick bark, so that wide stems were short with thicker bark for a given height. The fire resilience threshold for bark thickness differed between tall (4-5 mm) and wide individuals (8-9 mm), yet tall stems had lower P Topkill for a given bark thickness. Trends in P Topkill reflected eucalypt versus non-eucalypt differences. Eucalypts had thinner bark than non-eucalypts but lower P Topkill . With deeply embedded epicormic buds eucalypts do not need thick bark to protect buds and can allocate resources to height growth. Our data suggest the only 'strategy' for avoiding topkill in fireprone systems is to optimise bark thickness to maximise stem bud and cambium protection. Thus, escape height is the height at which bark protects the stem and a wide stem per se is insufficient protection from fire without thick bark. Consequently, absolute bark thickness is crucial to explanations of species differences in topkill, resprouting response and tree community composition in fire-prone savannas. Bark thickness and the associated mechanism of bud protection offer a proximate explanation for the dominance of eucalypts in Australian tropical savannas.

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Section: Discussionmentioning

confidence: 99%

How do small savanna trees avoid stem mortality by fire? The roles of stem diameter, height and bark thickness

et al. 2011

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“…There is less information on the effects of fire exclusion and the available information suggests the effects vary between systems (e.g. Lunt and Morgan 1999;Woinarski et al 2004;Gent and Morgan 2007). Short fire intervals (as experienced in frequent fires) are thought to result in the decline or disappearance of some species, most commonly obligate seeding shrubs, and the increase in other species with short maturation times, e.g.…”

Section: Introductionmentioning

confidence: 99%

Soil temperatures during autumn prescribed burning: implications for the germination of fire responsive species?

Penman

Towerton

2008

Int. J. Wildland Fire

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Prescribed fire is a widely applied management tool in native forests. There have been concerns raised about the ecological impacts of prescribed fire on native flora. One aspect of the debate is the extent towhich prescribed fire heats the soil to levels reported to trigger germination in the soil seed banks.We used Thermochrons to test soil temperatures at 2 and 5 cm in prescribed burns in dry sclerophyll forests. Soil temperatures during the burns were generally low (<40•C) with less than 5% of sites being exposed to temperatures necessary for the germination of fire-dependent shrub species. High temperatures were associated with high fuel consumption and large woody debris. This information suggests that prescribed fires, carried out according to standard practices, in these forests are unlikely to trigger germination in the majority of the soil-stored seed banks. If ecological burns in these forests are aimed at promoting populations of senescing obligate seeder species, they need to be hotter than standard practice if they are to achieve their objectives, although we acknowledge that there are inherent risks associated with hotter burns. Abstract. Prescribed fire is a widely applied management tool in native forests. There have been concerns raised about the ecological impacts of prescribed fire on native flora. One aspect of the debate is the extent to which prescribed fire heats the soil to levels reported to trigger germination in the soil seed banks. We used Thermochrons to test soil temperatures at 2 and 5 cm in prescribed burns in dry sclerophyll forests. Soil temperatures during the burns were generally low (<40 • C) with less than 5% of sites being exposed to temperatures necessary for the germination of fire-dependent shrub species. High temperatures were associated with high fuel consumption and large woody debris. This information suggests that prescribed fires, carried out according to standard practices, in these forests are unlikely to trigger germination in the majority of the soil-stored seed banks. If ecological burns in these forests are aimed at promoting populations of senescing obligate seeder species, they need to be hotter than standard practice if they are to achieve their objectives, although we acknowledge that there are inherent risks associated with hotter burns.

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“…There is increasing recognition that recurrent fire disturbance limits the dominance of trees and that without fire, the grass layer in mesic savannas is very much reduced and tree cover increases (Bond 2008, Bond et al 2005, Swaine et al 1992, Trapnell 1959, Woinarski et al 2004. Saplings are thought to be particularly vulnerable because stems in this size class are readily defoliated or killed by grass fires, yet are too large for their above-ground biomass to be quickly replaced from below-ground carbohydrate stores following top-kill, as happens for smaller stems (Hoffmann & Solbrig 2003).…”

Section: Introductionmentioning

confidence: 99%

Experimental evidence that fire causes a tree recruitment bottleneck in an Australian tropical savanna

2010

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Abstract:A fire-mediated recruitment bottleneck provides a possible explanation for the coexistence of trees and grasses in mesic savannas. The key element of this hypothesis is that saplings are particularly vulnerable to fire because they are small enough to be top-killed by grass fires, but unlike juveniles, they take several years to recover their original size. This limits the number of recruits into the adult size classes. Thus savanna vegetation may be maintained by a feedback whereby fire restricts the density of adult trees and allows a grass layer to develop, which provides fuel for subsequent fires. Here, we use results from a landscape-scale fire experiment in tropical Australia, to explore the possible existence of a recruitment bottleneck. This experiment compared tree recruitment and survival over 4 y under regimes of no fire, annual early and annual late dry-season fire. Stem mortality decreased with increasing stem height in the fire treatments but not in the unburnt treatment. Tree recruitment was 76-84% lower in the fire treatments than the unburnt treatment. Such fire-induced stem loss of saplings and reduced recruitment to the canopy layer in this eucalypt savanna are consistent with the predictions of the fire-mediated recruitment bottleneck hypothesis.

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Response of vegetation and vertebrate fauna to 23 years of fire exclusion in a tropical Eucalyptus open forest. Northern Territory, Australia

Cited by 85 publications

References 44 publications

How do small savanna trees avoid stem mortality by fire? The roles of stem diameter, height and bark thickness

How do small savanna trees avoid stem mortality by fire? The roles of stem diameter, height and bark thickness

Soil temperatures during autumn prescribed burning: implications for the germination of fire responsive species?

Experimental evidence that fire causes a tree recruitment bottleneck in an Australian tropical savanna

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