A Simple Model to Predict Scalar Dispersion within a Successively Thinned Loblolly Pine Canopy

Bark beetles kill millions of acres of trees in the United States annually by using chemical signaling to attack host trees en masse. As an attempt to control infestations, forest managers use synthetic semiochemical sources to attract beetles to traps and/or repel beetles from high-value resources such as trees and stands. The purpose of this study was to develop a simple numerical technique that may be used by forest managers as a guide in the placement of synthetic semiochemicals. The authors used a one-dimensional, one-equation turbulence model (k–lm) to drive a three-dimensional transport and dispersion model. Predictions were compared with observations from a unique tracer gas experiment conducted in a successively thinned loblolly pine canopy. Predictions of wind speed and turbulent kinetic energy compared well with observations. Scalar concentration was predicted well and trends of maximum observed concentration versus leaf area index were captured within 30 m of the release location. A hypothetical application of the numerical technique was conducted for a 12-day period to demonstrate the model’s usefulness to forest managers

A Simple Model to Predict Scalar Dispersion within a Successively Thinned Loblolly Pine Canopy

Bark beetles kill millions of acres of trees in the United States annually by using chemical signaling to attack host trees en masse. As an attempt to control infestations, forest managers use synthetic semiochemical sources to attract beetles to traps and/or repel beetles from high-value resources such as trees and stands. The purpose of this study was to develop a simple numerical technique that may be used by forest managers as a guide in the placement of synthetic semiochemicals. The authors used a one-dimensional, one-equation turbulence model (k–lm) to drive a three-dimensional transport and dispersion model. Predictions were compared with observations from a unique tracer gas experiment conducted in a successively thinned loblolly pine canopy. Predictions of wind speed and turbulent kinetic energy compared well with observations. Scalar concentration was predicted well and trends of maximum observed concentration versus leaf area index were captured within 30 m of the release location. A hypothetical application of the numerical technique was conducted for a 12-day period to demonstrate the model’s usefulness to forest managers

Plume Dispersion in Four Pine Thinning Scenarios: Development of a Simple Pheromone Dispersion Model

A unique field campaign was conducted in 2004 to examine how changes in stand density may affect dispersion of insect pheromones in forest canopies. Over a 14-day period, 126 tracer tests were performed, and conditions ranged from an unthinned loblolly pine (Pinus taeda) canopy through a series of thinning scenarios with basal areas of 32.1, 23.0, and 16.1 m2ha-1. In this paper, one case study was used to visualize the nature of winds and plume diffusion. Also, a simple empirical model was developed to estimate maximum average concentration as a function of downwind distance, travel time, wind speed, and turbulence statistics at the source location. Predicted concentrations from the model were within a factor of 3 for 82.1 percent and 88.1 percent of the observed concentrations at downwind distances of 5 and 10 m, respectively. In addition, the model was used to generate a field chart to predict optimum spacing in arrays of anti-aggregation pheromone dispensers

North American carbon dioxide sources and sinks: magnitude, attribution, and uncertainty

North America is both a source and sink of atmospheric carbon dioxide (CO2). Continental sources - such as fossil-fuel combustion in the US and deforestation in Mexico - and sinks - including most ecosystems, and particularly secondary forests - add and remove CO2 from the atmosphere, respectively. Photosynthesis converts CO2 into carbon as biomass, which is stored in vegetation, soils, and wood products. However, ecosystem sinks compensate for only similar to 35% of the continent's fossil-fuel-based CO2 emissions; North America therefore represents a net CO2 source. Estimating the magnitude of ecosystem sinks, even though the calculation is confounded by uncertainty as a result of individual inventory- and model-based alternatives, has improved through the use of a combined approach. Front Ecol Environ 2012; 10(10): 512-519, doi:10.1890/12006

A numerical study of turbulence, dispersion, and chemistry within and above forest canopies

This research focused on understanding turbulence, dispersion, and chemistry within and above forest canopies. In the first study, we used a one-dimensional turbulence model to calculate turbulent diffusivities for a three dimensional scalar transport model. The goal was to provide forest managers with quantitative data to guide them in the placement of synthetic pheromone traps for combating bark beetle infestations. The model is requires low computational resources, and thus is well suited for use in a web-based portal. In the second study, we developed two reduced chemical mechanisms for use in large eddy simulations (LES) of NOx-O3-VOC chemistry within and above a forest canopy. In the third study, we used LES to study the effect of vertical scalar source/sink distribution on scalar concentration moments, fluxes, and correlation coefficients within and above an ideal forest canopy. All scalar concentration moments, fluxes, and correlation coefficients were affected by the source location. In the final study, we used large eddy simulation (LES) to study non-linear effects of turbulent mixing on in-canopy NOx-O3-VOC chemistry for a northern hardwood forest located at the University of Michigan Biological Station (UMBS). We found that under daytime conditions at UMBS, non-linear effects of mixing on chemistry were not significant. However, simulations for a high radical environment showed that mixing significantly altered VR-BVOC oxidation, and NOx-O3 chemistry. As the canopy absorbed more momentum and/or O3 deposition to the canopy increased, the non-linear effect of mixing on chemistry increased, which suggests that the effect of non-linear mixing on chemistry is greater in tall, dense canopies as compared to shorter, less dense canopies

A numerical study of near-field dispersion within and above a forest canopy

The motivation for this project was to develop a tool to guide forest managers in protecting high value forest stands from bark beetle infestations. Several field experiments have been conducted in multiple forest canopies linking tracer gas concentration fields with meteorological and canopy parameters. Field experiments are often limited by cost, locations, and meteorological conditions. Numerical simulations are far less expensive and allow for many variations in flow parameters such as atmospheric stability, wind speed and direction. Near-field pheromone dispersion within and above a southern loblolly pine canopy with neutral and unstable atmospheric conditions was investigated using large eddy simulation (LES). LES captures coherent structures within and above the canopy which are responsible for the majority of scalar transport into and out of forest canopies. LES resolves large energy containing eddies while modeling smaller dissipative eddies using a sub grid scale model. The model incorporates canopy effects based on leaf area index (LAI), leaf area density (LAD), and stem density. Convective conditions are also modeled using a heat source term based on above canopy heat flux. Results of the LES are compared with experimental data from a recent tracer gas field study. The LES solution predicts higher mean velocity and concentration within the canopy, but demonstrates similar instantaneous trends for velocity and concentration