Developing shrub fire behaviour models in an oceanic climate: Burning in the British Uplands

Abstract

Prescribed burning of moorland vegetation in the UK is used to provide habitat for red grouse, a game bird, and to improve grazing for sheep and deer. The peak time of fire risk corresponds to the normal legal burning period of 1st November (1st October in Scotland) to 15th April rather than a meteorologically-defined fire season.

Moorland fuels in the UK are unusual. They are dominated by Calluna vulgaris, which forms a dense, uniform canopy (though as stands age gaps become more frequent), and in which live material forms the majority of “available” fuel. The moisture content of live fuel plays a dominant role in determining fire behaviour. Weather in the UK uplands can vary rapidly from cold and wet, to sunny with drying winds and low atmospheric humidity. Frozen ground can prevent plants from replenishing water lost by transpiration. Fire behaviour is difficult to predict and periods of significant wildfire activity can occur.

Data from 15 experimental fires were used to build empirical relationships between rate of spread, windspeed and vegetation structure. Fires in the high fuel-loads responded much more strongly to increased windspeed. The high density of the fuel-bed in younger Calluna stands may have a limiting effect on the rate of fire spread. Redundancy analysis highlights the importance of fuel moisture content and stand structural heterogeneity.

We tested the rate of spread predictions of BehavePlus and the Canadian Wildland Fire Information System (CWFIS). Predictions provided by BehavePlus were relatively good. The CWFIS was unable to predict rate of spread because the moisture content of live and dead Calluna was not accurately predicted by any of the moisture codes of the CWFIS. The system did detect a period of extreme risk associated with drought and wildfires during the spring of 2003. Multiple scales and causal factors of increased fire risk are discussed with reference to seasonal variation in the fuel moisture content of Calluna.