Can burning restrict eucalypt invasion on grassy balds?

Fensham, R. J.; Fairfax, R. J.

doi:10.1111/j.1442-9993.2006.01560.x

Cited by 34 publications

(34 citation statements)

References 22 publications

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“…Other possible explanations for the absence of trees in upland grasslands have included thermal constraints on growth or survival (e.g. frost damage; Acocks 1953), fire (Bragg and Hulbert 1976;Fairfax et al 2009), fire and grazing (Mark 1958;Knapp et al 1999), climate (Weaver 1954Webb 1964), grass competition (Walter 1979), and seed dispersal (Fensham and Fairfax 2006). Despite similar biogeographical patterns around the globe, there is as yet no conceptual framework or general explanation for the tree-less nature of upland C 4 grasslands.…”

Section: Variablementioning

confidence: 99%

Is the lack of leguminous savanna trees in grasslands of South Africa related to nutritional constraints?

2010

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As with many grasslands globally, the Highveld grasslands of South Africa are tree-less, despite having a climate that can support tree growth. Models predict that fire maintains these grasslands. The question arises as to why fire-tolerant savanna trees do not survive in these ecosystems? Savanna tree survival in mesic areas is restricted by demographic bottlenecks, specifically limitations to sapling-escape from fire. It was hypothesised that ancient highly leached soils from grassland areas would prevent saplings from growing fast enough to escape the fire-trap. Growth rates of savanna tree seedlings (Acacia karroo Hayne and Acacia sieberiana Burtt Davy) were measured in a common garden experiment using soils from ten sites collected along a savanna-grassland continuum. Soils from grassland sites were relatively nutrient-poor compared to those from savannas with lower pH, and associated cations. A. sieberiana growth rates responded to pH and these nutrients, whereas A. karroo growth was less strongly linked to specific nutrients. Even so, both species accumulated more biomass when grown in soils from savanna sites compared to grassland sites. An exception was a low elevation low nutrient savanna site that resulted in poor growth, yet sustains high tree biomass in situ. Differences between growth in grassland and savanna soils were small. They may contribute to, but are unlikely to explain, the treeless nature of these grasslands.

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Section: Variablementioning

confidence: 99%

Is the lack of leguminous savanna trees in grasslands of South Africa related to nutritional constraints?

2010

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“…Nonetheless, even some resprouting plants may decline if they are unable to grow beyond scorch height in the period between fires or if repeated defoliation depletes starch reserves (Walters et al 2005;Fensham & Fairfax 2006). Thus, repeated burning over a long period of time has the potential to reduce the density and richness of native understorey plants that cannot survive the effects of repeated burning or reproduce between burns.…”

Section: Introductionmentioning

confidence: 96%

The effect of long‐term repeated burning and fire exclusion on above‐ and below‐ground Blackbutt (Eucalyptus pilularis) forest vegetation assemblages

et al. 2012

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We used a long-term fire experiment in south-east Queensland, Australia, to determine the effects of frequent prescribed burning and fire exclusion on understorey vegetation (<7.5 m) richness and density in Eucalyptus pilularis forest. Our study provided a point in time assessment of the standing vegetation and soilstored vegetation at two experimental sites with treatments of biennial burning, quadrennial burning since 1971-1972 and no burning since 1969. Vegetation composition, density and richness of certain plant groups in the standing and soil-stored vegetation were influenced by fire treatments. The density of resprouting plants <3 m in height was higher in the biennially burnt treatment than in the unburnt treatment, but resprouters 3-7.5 m in height were absent from the biennial burning treatment. Obligate seeder richness and density in the standing vegetation was not significantly influenced by the fire treatments, but richness of this plant group in the seed bank was higher in the quadrennial treatment at one site and in the long unburnt treatment at the other site. Long unburnt treatments had an understorey of rainforest species, while biennial burning at one site and quadrennial burning at the other site were associated with greater standing grass density relative to the unburnt treatment. This difference in vegetation composition due to fire regime potentially influences the flammability of the standing understorey vegetation. Significant interactions between fire regime and site, apparent in the standing and soil-stored vegetation, demonstrate the high degree of natural variability in vegetation community responses to fire regimes.

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“…Essentially, there is little evidence to support bottom‐up explanations of bald locations, such as soil depth or frost proneness (Fensham & Fairfax, ). Of the possible top‐down controls, fire is consistently supported as a powerful influence on populations of rain forest species (Fairfax et al ., ) but its capacity to control eucalypts and stabilize savanna–bald boundaries is questionable (Fensham & Fairfax, ). Other top‐down influences, such as kangaroo grazing, are considered unlikely to have a strong influence because grazers are fairly uncommon and the grazing regime has not been modified to nearly the same extent at a landscape scale as fire has over the last two centuries; the grasslands were not used for livestock grazing, except near settlements, because of their remoteness and intractability.…”

Section: Methodsmentioning

confidence: 99%

Aborigine‐managed forest, savanna and grassland: biome switching in montane eastern Australia

Butler¹,

Fensham

Murphy

et al. 2014

Journal of Biogeography

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Aim To assess hypotheses about the role of anthropogenic fire in the maintenance and origin of a fine‐scale vegetation mosaic of rain forest, eucalypt savanna and grassland. Location Bunya Mountains, subtropical eastern Australia. Methods A time series of vegetation maps was compiled from historical and recent aerial photography and field surveys. Geospatial models were constructed of environmental domains for rain forest, savanna and grassland, and for areas of biome change. Grassland soils were analysed for carbon isotope ratios (δ13C), and radiocarbon (14C) dates were acquired for bulk samples from a range of depths. Results Analysis revealed weak associations between topography and the distribution of rain forest, savanna and grassland, and their patterns of recent change. Grassland occupied an environmental domain intermediate between rain forest and savanna and was more than four times as likely to occur within a matrix of rain forest rather than savanna. There was a large proportional reduction in the area of both grassland (−35%) and savanna (−19%) between 1961 and 2006 because of the expansion of rain forest. However, the greater initial extent of savanna meant that the areal loss of savanna was an order of magnitude greater than for grassland (1433 vs. 146 ha). There was no evidence of abrupt changes in δ13C in grassland soil profiles, indicating stability of the vegetation over the last 2000 years. Main conclusions There is no simple gradient in ‘tree suitability’ from rain forest, through savanna, to treeless grassland on the Bunya Mountains. A general absence of fire since the 19th century has greatly reduced the extent of grassy savanna and grassland formations, to the advantage of rain forest. These results support the hypothesis that the vegetation mosaic on the Bunya Mountains is a cultural artefact and testament to millennia of skilful and persistent burning. We could not conclusively reject the hypothesis that the grasslands are Pleistocene relicts that have declined throughout the Holocene; nonetheless, an explanation more consistent with the evidence overall is that the grasslands must have had periods of expansion during the Holocene, probably as a consequence of severe fires that have destroyed patches of rain forest.

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Can burning restrict eucalypt invasion on grassy balds?

Cited by 34 publications

References 22 publications

Is the lack of leguminous savanna trees in grasslands of South Africa related to nutritional constraints?

Is the lack of leguminous savanna trees in grasslands of South Africa related to nutritional constraints?

The effect of long‐term repeated burning and fire exclusion on above‐ and below‐ground Blackbutt (Eucalyptus pilularis) forest vegetation assemblages

Aborigine‐managed forest, savanna and grassland: biome switching in montane eastern Australia

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