The Effect of Fuel Moisture Content on the Flammability of Goldenrod in Prairie Ecosystems

Madeline Reuschling
Undergraduate (Environmental & Plant Sciences)
Dr. Matt Davies
Environment and Natural Resources

Canadian goldenrod (Solidago canadensis) is a native species but it can become invasive within restored prairies and old fields creating monocultures that reduce the species richness and diversity. Fire, is a vital ecological disturbance within prairies but goldenrod-dominated areas are often difficult to ignite and burn. To better understand fundamental controls on the potential for prescribed burning in restored prairies the flammability of goldenrod was investigated. Field data was collected during spring and fall 2019 to determine variation in fuel moisture content (FMC) with weather and how FMC varies vertically through the fuel bed. Weather data was taken on sampling days from Waterman Farm weather station and applied to the Canadian Forest Fire Danger Rating System to calculate the daily Fine Fuel Moisture Code (FFMC). Lab tests were conducted by heating samples of goldenrod of different FMCs in a quartz epiradiator and measuring ignitability, sustainability and combustibility. The impact of a pilot flame on ignition processes was also examined. Goldenrod FMC was lowest at the top of plants in spring, with greater fire danger ratings. Fall FMC was not impacted by fire danger rating. Flammability tests showed that time to ignition was shortest at low FMCs. The duration of flaming and flame heights were greatest with lower FMCs. When comparing the flammability metrics to the FFMC values calculated from field data, there was a correlation between greater flammability and greater FFMC. Overall, the results indicated that flammability was greatest at the lowest fuel moisture contents, specifically around 15-20% of lower. The flammability metrics determined that faster ignition, higher flame heights and longer durations of flaming would likely lead to the spread of fire throughout fuels and greater consumption of goldenrod. Field data suggests that goldenrod has the lowest fuel moisture content in spring, at the top of the plant, which can alter fire behavior by leading to less surface fires and more crown fires. Fine fuel moisture codes increased with decreasing fuel moisture contents and were positively correlated to flammability metrics. Fine fuel moisture codes of 74-80 and above strongly indicate increased flammability of goldenrod.