Moisture desorption in mechanically masticated fuels: effects of particle fracturing and fuelbed compaction

Mechanical mastication is increasingly used as a wildland fuel treatment, reducing standing trees and shrubs to compacted fuelbeds of fractured woody fuels. One major shortcoming in our understanding of these fuelbeds is how particle fracturing influences moisture gain or loss, a primary determinant of fire behaviour. To better understand fuel moisture dynamics, we measured particle and fuelbed drying rates of masticated Arctostaphylos manzanita and Ceanothus velutinus shrubs, common targets of mastication in fire-prone western USA ecosystems. Drying rates of intact and fractured particles did not differ when desorbing at the fuelbed surface, but these particles did dry more rapidly than underlying fuelbeds. Average response times of 10-h woody particles at the fuelbed surfaces ranged from 16 to 21 h, whereas response times of fuelbeds (composed of 1-h and 10-h particles) were 40 to 69 h. Response times did not differ between fuelbeds composed of fractured woody particles and fuelbeds composed of intact particles (P = 0.258). Particle fracturing as a result of mastication does not affect the drying rate, but the longer-than-expected response times of particles within fuelbeds underscores the needs to better understand fuel moisture dynamics in these increasingly common fuels.