SF6 Tracer Gas Experiment in Cherry Canopy

Bark beetle infestations in western North America have severe negative biogeophysical and biogeochemical impacts that affect millions of hectare of forestry. The beetles kill apparently healthy trees by attacking en masse to overcome host tree resistance, and then adequately space themselves to limit interspecies competition. Both processes involve using pheromone to communicate. To protect high value stands, forest managers use synthetic pheromones to repel or attract beetles to traps. By adequately placing synthetic attractants and anti-aggregation semiochemicals, forest managers can protect trees and forested areas from bark beetle attacks. However, there is a lack of information to guide them.

In this experiment, we set up a simulation to graph the correspondence between tracer gas concentration and atmospheric stability. Within the canopy, we set up three sonic anemometers to measure the wind and temperature in order to produce distribution profiles from the measurements. Concurrently, we set up the Tracer Gas Automated Profiling System or T-GAPS to measure sulfur hexafluoride: an inert gas that is not commonly found in ambient air and is easily traceable. The release is set within the canopy with sampling tubes surrounding it in a concentric circle. This allows us to analyze the tracer sample continuously with five minute average concentration measurements. By statistical data analysis, we can find a correlation between the plume concentrations and atmospheric conditions such as turbulence, stability, and etc. The long-term tracer gas dispersion that is collected is anticipated to be used to improve models used by forest managers and thus protect high value forest stands.