Alpine grazing: does it reduce blazing?

Williams R.J., Wahren C.H.A., Bradstock R.A., Muller W.J. (2006) Does alpine grazing reduce blazing? A landscape test of a widely-held hypothesis. Austral Ecology 31, 925–936.

Aim: 
To evaluate, at a landscap-scale, the effect of livestock grazing on the extent and severity of the 2003 fires in treeless alpine landscapes.
Type of Study: 
Natural experiment
Key Results: 
Approximately half of all points were burnt. There was no statistically significant difference between grazed and ungrazed areas in the proportion of points burnt. Fire occurrence was determined primarily by vegetation type, with the proportion burnt being 0.87 for closed-heath, 0.59 for open-heath, and 0.13 for grassland and all snow-patch herbfield points unburnt. In both closed-heath and open-heath, grazing did not significantly lower the severity of fire, as measured by the diameter of burnt twigs. (pp. 925)
Treatments: 
Transect lines has at least 10 sample points per line. Sample points had varying vegetation type (closed-heath, open-heath, grassland or herbfield), slope and aspect. Half of transects located in grazed areas, half in ungrazed areas. For heathlands, twigs nested within shrubs within individual sample points.
Models: 
Frequentist (P values): Nested ANOVA; logistic regression (model deviance and P values) and semivariograms; power sensitivity analysis for grazing treatment.
Comments: 
Clear and robust test of the hypothesis that alpine grazing reduces blazing. The evidence clearly shows the hypothesis to be unsupported by field evidence from the Bogong High Plains.
Reviewer: 
Imogen Fraser; Dick Williams
Locations: 
Bogong High Plains, Australian Alpine National Park, Victoria, Australia
Response variable : 
Whether the site was burnt or unburnt, minimum diameter of burnt twigs (burnt heathland sites only).
Replication: 
Fire occurrence recorded at 419 sites; 4050 twig measurements made at 286 heathland sites; 10 shrubs per site. Approximately half the sites were grazed by cattle at the time of the fire, and approximately half had been ungrazed since 1991.
Ecosystem: 
Alpine closed heathland, open heathland, grassland and herbfield.
Full Reference: 
Williams R.J., Wahren C.H.A., Bradstock R.A., Muller W.J. (2006) Does alpine grazing reduce blazing? A landscape test of a widely-held hypothesis. Austral Ecology 31, 925–936.