Epsilon Archive for Student Projects

Abstract

Fire activity is influenced by weather and climate, fuels, ignition agents, and human activities. Fire
suppression policy in Sweden resulted in a gradual decrease in the annually burnt areas, changes in
fuel loads and a decline in species diversity. Prescribed burning is recommended as a management
tool for fire-prone ecosystems to support conservation policies and, eventually, mitigate large high-intensity
wildfires.
This study analysed fire behaviour as a function of fuel characteristics and weather conditions in
oak dominated forests in Southern Sweden. I was specifically interested in thresholds indicative of
accelerated fire spread and conditions leading to increased consumption of ground fuels. I also
studied whether regional weather indices provide predictive power with respect to local fire
behaviour. Data from 105 ignition experiments at seven study sites laid the ground for the database
used in analyses. Data collection involved the collection of meteorological on-site data, pre- and
post-fire fuel inventories, and measurements of fire behaviour.
The minimum wind above 2.5 m/s and the temperature above 15°C positively affected fire spread.
High relative humidity and the low amount of dry fuel had a negative effect on fire spread. The fire
spread slowed down when the value of relative humidity exceeded 35 % and the fuel amount
dropped below 1000 g/m2. Fire spread slowed down when the relative humidity exceeded 40 %, and
litter depth fell below 0.05 m. Total fuel consumption grew when the fuel amount exceeded
3000 g/m2 and the fire spread rate fell below 0.05 m/s. Fuel amount and relative humidity affected
total consumption. Total consumption grew when the fuel amount exceeded 1800 g/m2, while the
relative humidity fell below 30 %. Regional weather indices were poor predictors of fire behaviour.
The study identifies thresholds of fire behaviour in oak dominated forests that can be used by forest
managers to plan prescribed burnings. The study highlights the need for further research covering a
wider gradient of weather conditions.