A Tracer Investigation of Pheromone Dispersion in a Lodgepole Pine Forest Canopy

Abstract

To improve our understanding of the transport of insect pheromone through a forest canopy, tracer experiments were conducted in 2000 amid a lodgepole pine (Pinus contorta) forest in Montana. Six tests were analyzed to visualize relationships between wind direction and plume behavior for downwind distances of 5, 10, and 30 m. Time series of sulfur hexafluoride showed intennittent plume events with peak-to-mean ratios as high as 81 at the 10-m arc. Average dispersion coefficients ranged approximately 4-8 m at the 5-m arc, 9-17 m at the 10-m arc, and 27-45 m at the 30-m arc. In addition, a simple empirical equation was developed to estimate average plume spread on these scales as a function of standard turbulence statistics and travel time. Predicted dispersion coefficients were within a factor of 2, or better, of observed values for 95% of the cases, and the average predicted-to-observed ratio was 1.07 for the dataset of 158 plume profiles. Results from this field campaign were site-specific, but they were part of a larger effort by the United States Department of Agriculture (USDA) Forest Service to characterize dispersion in a variety of forest types