Disturbance causes variation in sub-canopy fire weather conditions
Agricultural and Forest Meteorology
Disturbance history is known to affect fire risk by altering fuel dynamics, but the effects of disturbance on micro-meteorological conditions that influence fire are poorly understood. Logging and wildfire can significantly alter the height and density of vegetation in forests. These structural attributes can influence aspects of the sub-canopy microclimate that may influence forest flammability. We used portable weather stations to measure the effects of time since logging and time since wildfire on air temperature, relative humidity, vapour pressure deficit and windspeed at 119 sites in coastal forest in south-eastern Australia. These data were used to calculate fuel moisture and within forest Forest Fire Danger Index (FFDI). Data were collected on 345 days (12 days per site on average), over three consecutive fire seasons. Temperature, vapour pressure deficit, windspeed and forest FFDI all decreased with time since logging, while relative humidity and fuel moisture content increased. Windspeeds also decreased with time since wildfire. These effects continued for at least 60 years after disturbance. Over the duration of our study, fuel was available to burn (below 16% fuel moisture content) 1.4 times more often in recently logged sites (zero years since logging) compared to sites that had not been logged for 71 years. Recently logged sites were also predicted to have a high Fire Danger Rating (FFDI = 12–24) on 24 days, compared to just two days at sites last logged 71 years ago. Our findings indicate that the changes in vegetation associated with logging and to a lesser extent wildfire, increase the risk of fire. This research provides new insights into the effects of antecedent logging and wildfire on forest flammability that can be used to inform the management of fire prone forests.
Open Access Status
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Ecological Society of Australia