Fluctuations in fuel moisture across restoration treatments in semi-arid ponderosa pine forests of northern Arizona, USA

Fuel moisture is an important variable in estimating fire behaviour and wildfire hazard. We measured three replicates each of thin- and-burn, burn-only, and control treatments in semi-arid ponderosa pine forests of northern Arizona, USA to quantify temporal changes and treatment effects on live foliar and dead fuel moisture content. Overstorey structure and canopy bulk density were reduced 40-75% in the thin- and-burn treatment v. the burn-only and control treatments. Fluctuations in foliar moisture content varied temporally and across study areas. In 2003, a significant treatment effect was found for two study sites for 1-year-old foliage, but no significant treatment effect was found for new foliage. In 2004, a significant treatment effect was found across all three study sites for both 1-year-old and new foliage. However, no clear pattern existed regarding a specific treatment and its effect on moisture content of old or new foliage. No conclusive evidence was found for a significant treatment effect on the moisture content of fuel particles in the size classes of 0-6, 6-25, and 25-100-mm diameter. Proposals regarding amplified fire behaviour as a consequence of reduced fuel moisture contents in treated v. untreated forest stands in semi-arid ponderosa pine forests of northern Arizona therefore appear to be unwarranted.