Monitoring seasonal transpiration drying of loblolly and slash pine with time domain reflectometry

The moisture content (MC) of felled trees has a direct impact on transportation costs and efficiency. Transpirational (or field) drying of fallen trees, to reduce MC and subsequently improve the economics of transport can be employed; however, an understanding of seasonal drying rates is required. Typically load cells have been used to track moisture changes in bundles of logs but where access is limited this approach is impractical. Time-domain reflectometry (TDR) provides an alternative approach and was used to monitor seasonal changes in transpirational drying rates for felled loblolly and slash pine at a Lower Coastal Plain site in Florida and loblolly pine at a Piedmont site in Georgia on a weekly basis for approximately one year. Different transpirational drying rates and minimum MC’s were observed by season. Drying rates observed during summer, fall and spring, at both test locations, indicate that after three weeks an equilibrium (or minimum) MC is achieved. Winter drying is slower, and up to 5 weeks in the field (or even longer) may be required. Post equilibrium felled log moisture content continued to vary during most seasons with rainfall events the most probable cause. TDR provides a viable approach for monitoring transpirational drying and subsequent MC changes in felled trees.