Frequent fire promotes diversity and cover of biological soil crusts in a derived temperate grassland |
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Authors: | Katharine E O’Bryan Suzanne Mary Prober Ian D Lunt David J Eldridge |
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Institution: | (1) Institute for Land, Water and Society, Charles Sturt University, PO Box 789, Albury, NSW, 2640, Australia;(2) CSIRO Sustainable Ecosystems, Private Bag 5, Wembley, WA, 6913, Australia;(3) Department of Environment and Climate Change, School of Biological, Earth and Environmental Sciences, University of NSW, Sydney, NSW, 2052, Australia |
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Abstract: | The intermediate disturbance hypothesis (IDH) predicts that species diversity is maximized at moderate disturbance levels.
This model is often applied to grassy ecosystems, where disturbance can be important for maintaining vascular plant composition
and diversity. However, effects of disturbance type and frequency on cover and diversity of non-vascular plants comprising
biological soil crusts are poorly known, despite their potentially important role in ecosystem function. We established replicated
disturbance regimes of different type (fire vs. mowing) and frequency (2, 4, 8 yearly and unburnt) in a high-quality, representative
Themeda australis–Poa sieberiana derived grassland in south-eastern Australia. Effects on soil crust bryophytes and lichens (hereafter cryptogams) were measured
after 12 years. Consistent with expectations under IDH, cryptogam richness and abundance declined under no disturbance, likely
due to competitive exclusion by vascular plants as well as high soil turnover by soil invertebrates beneath thick grass. Disturbance
type was also significant, with burning enhancing richness and abundance more than mowing. Contrary to expectations, however,
cryptogam richness increased most dramatically under our most frequent and recent (2 year) burning regime, even when changes
in abundance were accounted for by rarefaction analysis. Thus, from the perspective of cryptogams, 2-year burning was not
an adequately severe disturbance regime to reduce diversity, highlighting the difficulty associated with expression of disturbance
gradients in the application of IDH. Indeed, significant correlations with grassland structure suggest that cryptogam abundance
and diversity in this relatively mesic (600 mm annual rainfall) grassland is maximised by frequent fires that reduce vegetation
and litter cover, providing light, open areas and stable soil surfaces for colonisation. This contrasts with detrimental effects
of 2-year burning on native perennial grasses, indicating that this proliferation of cryptogams has potentially high functional
significance for situations where vegetation cover is depleted, particularly for reducing soil erosion. |
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Keywords: | Cryptogams Burning Fire frequency Intermediate disturbance hypothesis Mowing |
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