Surrogate Pheromone Plumes in Three Forest Trunk Spaces: Composite Statistics and Case Studies

An atmospheric tracer gas was used as a pheromone surrogate to study near-field canopy dispersion within the trunk space. The objective is to improve guidance for forest managers deploying bark beetle antiaggregation pheromone sources to protect high- value forest stands. Data are shown from field studies in three forest canopies (oak-hickory, Quercus-Carya; lodgepole pine, Pinus contorta Dougl. ex Loud.; and ponderosa pine, Pinus ponderosa Dougl. ex Laws.) and include over 13,000 chemical tracer samples compiled into half-hour dispersion fields around a point source. Maximum normalized concentrations (~10) at each arc distance for each sampling period were of similar order at 5 m from the tracer source in the three canopies, although the differences in maximum xIQ between canopies increased with distance from the source. Plume dilution was highest in this study in the more open ponderosa pine canopy. A high-frequency tracer gas analyzer was also deployed to ascertain the structure of the gas plumes at 1 Hz. The high-frequency tracer data showed that the 30-minute average mean plumes are composites of narrow filamentous plumes. The near-field plumes in each canopy were strongly affected by changes in atmo- spheric stability, as wander range and meander frequency increased after the morning transition to an unstable boundary layer. FOR. SCI. 50(5):610-625.