Fire controls population structure in four dominant tree species in a tropical savanna

Lehmann, Caroline E. R.; Prior, Lynda D.; Bowman, David M. J. S.

doi:10.1007/s00442-009-1395-9

Cited by 54 publications

(58 citation statements)

References 38 publications

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“…For example, there was a paucity of saplings in Kapalga in 1982, although by 1991, many saplings were evident, and stand structure exhibited a classic reverse-J curve (Prior et al 2006). Lehmann et al (2009a) examined stand structures of four major species in Kakadu National Park in 2003, and found no evidence of gaps in recruitment at a regional level, but noted that at a local level regeneration appeared episodic because some size classes were underrepresented.…”

Section: Relative Juvenile Abundancementioning

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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Section: Relative Juvenile Abundancementioning

confidence: 99%

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

2010

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“…Repeated topkill of small trees prevents recruitment into adult size classes and may 'trap' individual stems in the flame zone (sensu Midgley and Bond 2001). In fact, the suppressive effect of fire on small savanna trees is such that topkill has become an accepted driver of savanna dynamics worldwide (Higgins et al 2000, Hoffmann and Solbrig 2003, Balfour and Midgley 2006, Higgins et al 2007, Lehmann et al 2009). Clearly, trees that are resilient to the damaging effects of fire and can avoid topkill will be advantaged in fire-prone savannas.…”

Section: Introductionmentioning

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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“…Many of these fires occur late in the dry season, producing high intensity burns that result in simplified 10 vegetation structure (Bowman et al, 1988;Lehmann et al, 2009;Ondei et al, 2017). There are widespread concerns that such fire regimes are linked to dramatic declines in faunal populations, through the removal of ground layer vegetation (Lawes et al, 2015;Legge et al, 2015;Woinarski et al, 2015).…”

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Rapid response of habitat structure and aboveground carbon storage to altered fire regimes in tropical savanna

Levick¹,

Richards²,

Cook³

et al. 2018

Preprint

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Abstract. Fire regimes across the globe have been altered through changes in land-use, land management and climate conditions. Understanding how these modified fire regimes impact vegetation structure and dynamics is essential for informed biodiversity conservation and carbon management in savanna ecosystems. We used a long-term fire experiment at the Territory Wildlife Park (TWP), northern Australia, to investigate the consequences of altered fire regimes for habitat structure and aboveground carbon storage. We mapped vegetation three-dimensional (3D) structure in high spatial resolution with airborne ), and analysed differences in aboveground carbon storage and 3D structure among treatments. Woody canopy cover and biomass were highest in the absence of fire (76 % and 39.8 t C ha ). Woody canopy vertical profiles differed among all six fire treatments, 10 with greatest divergence in height classes < 5m. Our results highlight the large extent to which fire management can shape 3D structural patterns in savanna landscapes, even over time frames as short as a decade. The structural profile changes shown here, and the quantification of carbon reduction under late dry season burning, have important implications for faunal habitat conservation and carbon sequestration/emission reduction initiatives in the region.

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Fire controls population structure in four dominant tree species in a tropical savanna

Cited by 54 publications

References 38 publications

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

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

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

Rapid response of habitat structure and aboveground carbon storage to altered fire regimes in tropical savanna

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