Modifying the Canadian Fine Fuel Moisture Code for masticated surface fuels

Mechanical mastication is a fuel management technique that disrupts the vertical continuity of forest fuels by shredding of trees and understory vegetation into a highly compacted surface fuel bed. Despite the increasing application of mastication to manage wildfire risk, there is little information to date on fuel moisture in masticated fuels and optimal ignition patterns for prescribed burning. We investigated the applicability of the Fine Fuel Moisture Code (FFMC), a component of the Canadian Fire Weather Index (FWI) System, in tracking the diurnal and day-to-day changes in masticated surface fuel moisture, and developed a calibration of the standard conversion between moisture content and FFMC via regression modelling. We also proposed several modifications to the FFMC model (including a solar radiation driven fuel temperature) to better estimate the fuel-specific parameters of small diameter (<1 cm) masticated surface fuels. Model validation was performed using destructive moisture content observations from a mastication treatment in west-central Alberta, Canada. A calibrated form of the moisture content to FFMC conversion produced mean error of –2.3% moisture content, and closely resembled previous FWI System calibrations for fast drying surface fuels. Our modified FFMC-based model fit well with field observations, and was capable of producing mean error of 1.0% moisture content. The fast drying that we observed highlights the need to better understand moisture dynamics of masticated fuel beds.