Steven L. Edburg

Simulating the Impacts of Disturbances on Forest Carbon Cycling in North America: Processes, Data, Models, and Challenges

[1] Forest disturbances greatly alter the carbon cycle at various spatial and temporal scales. It is critical to understand disturbance regimes and their impacts to better quantify regional and global carbon dynamics. This review of the status and major challenges in representing the impacts of disturbances in modeling the carbon dynamics across North America revealed some major advances and challenges. First, significant advances have been made in representation, scaling, and characterization of disturbances that should be included in regional modeling efforts. Second, there is a need to develop effective and comprehensive process‐based procedures and algorithms to quantify the immediate and long‐term impacts of disturbances on ecosystem succession, soils, microclimate, and cycles of carbon, water, and nutrients. Third, our capability to simulate the occurrences and severity of disturbances is very limited. Fourth, scaling issues have rarely been addressed in continental scale model applications. It is not fully understood which finer scale processes and properties need to be scaled to coarser spatial and temporal scales. Fifth, there are inadequate databases on disturbances at the continental scale to support the quantification of their effects on the carbon balance in North America. Finally, procedures are needed to quantify the uncertainty of model inputs, model parameters, and model structures, and thus to estimate their impacts on overall model uncertainty. Working together, the scientific community interested in disturbance and its impacts can identify the most uncertain issues surrounding the role of disturbance in the North American carbon budget and develop working hypotheses to reduce the uncertainty.

Cascading impacts of bark beetle‐caused tree mortality on coupled biogeophysical and biogeochemical processes

Recent, large-scale outbreaks of bark beetle infestations have affected millions of hectares of forest in western North America, covering an area similar in size to that impacted by fire. Bark beetles kill host trees in affected areas, thereby altering water supply, carbon storage, and nutrient cycling in forests; for example, the timing and amount of snow melt may be substantially modified following bark beetle infestation, which impacts water resources for many western US states. The quality of water from infested forests may also be diminished as a result of increased nutrient export. Understanding the impacts of bark beetle outbreaks on forest ecosystems is therefore important for resource management. Here, we develop a conceptual framework of the impacts on coupled biogeophysical and biogeochemical processes following a mountain pine beetle (Dendroctonus ponderosae) outbreak in lodgepole pine (Pinus contorta Douglas var latifolia) forests in the weeks to decades after an infestation, and highlight fu...

Direct measurements show decreasing methane emissions from natural gas local distribution systems in the United States.

Fugitive losses from natural gas distribution systems are a significant source of anthropogenic methane. Here, we report on a national sampling program to measure methane emissions from 13 urban distribution systems across the U.S. Emission factors were derived from direct measurements at 230 underground pipeline leaks and 229 metering and regulating facilities using stratified random sampling. When these new emission factors are combined with estimates for customer meters, maintenance, and upsets, and current pipeline miles and numbers of facilities, the total estimate is 393 Gg/yr with a 95% upper confidence limit of 854 Gg/yr (0.10% to 0.22% of the methane delivered nationwide). This fraction includes emissions from city gates to the customer meter, but does not include other urban sources or those downstream of customer meters. The upper confidence limit accounts for the skewed distribution of measurements, where a few large emitters accounted for most of the emissions. This emission estimate is 36% to 70% less than the 2011 EPA inventory, (based largely on 1990s emission data), and reflects significant upgrades at metering and regulating stations, improvements in leak detection and maintenance activities, as well as potential effects from differences in methodologies between the two studies.

The canopy horizontal array turbulence study

The Canopy Horizontal Array Turbulence Study (CHATS) took place in spring 2007 and is the third in the series of Horizontal Array Turbulence Study (HATS) experiments. The HATS experiments have been instrumental in testing and developing subfilterscale (SFS) models for large-eddy simulation (LES) of planetary boundary layer (PBL) turbulence. The CHATS campaign took place in a deciduous walnut orchard near Dixon, California, and was designed to examine the impacts of vegetation on SFS turbulence. Measurements were collected both prior to and following leafout to capture the impact of leaves on the turbulence, stratification, and scalar source/sink distribution. CHATS utilized crosswind arrays of fast-response instrumentation to investigate the impact of the canopy-imposed distribution of momentum extraction and scalar sources on SFS transport of momentum, energy, and three scalars. To directly test and link with PBL parameterizations of canopy-modified turbulent exchange, CHATS also included a 30-m profile ...

Direct and Indirect Measurements and Modeling of Methane Emissions in Indianapolis, Indiana

This paper describes process-based estimation of CH4 emissions from sources in Indianapolis, IN and compares these with atmospheric inferences of whole city emissions. Emissions from the natural gas distribution system were estimated from measurements at metering and regulating stations and from pipeline leaks. Tracer methods and inverse plume modeling were used to estimate emissions from the major landfill and wastewater treatment plant. These direct source measurements informed the compilation of a methane emission inventory for the city equal to 29 Gg/yr (5% to 95% confidence limits, 15 to 54 Gg/yr). Emission estimates for the whole city based on an aircraft mass balance method and from inverse modeling of CH4 tower observations were 41 ± 12 Gg/yr and 81 ± 11 Gg/yr, respectively. Footprint modeling using 11 days of ethane/methane tower data indicated that landfills, wastewater treatment, wetlands, and other biological sources contribute 48% while natural gas usage and other fossil fuel sources contribute 52% of the city total. With the biogenic CH4 emissions omitted, the top-down estimates are 3.5-6.9 times the nonbiogenic city inventory. Mobile mapping of CH4 concentrations showed low level enhancement of CH4 throughout the city reflecting diffuse natural gas leakage and downstream usage as possible sources for the missing residual in the inventory.

The Effect of the Vertical Source Distribution on Scalar Statistics within and above a Forest Canopy

Little is known about in-canopy processes that may alter forest–atmosphere exchanges of trace gases and aerosols. To improve our understanding of in-canopy mixing, we use large-eddy simulation to study the effect of scalar source/sink distributions on scalar concentration moments, fluxes, and correlation coefficients within and above an ideal forest canopy. Scalars are emitted from: (1) the ground, (2) the canopy, and (3) both the ground and the canopy; a scalar is also deposited onto the canopy. All scalar concentration moments, fluxes, and correlation coefficients are affected by the source location/distribution, as is the scalar segregation intensity. We conclude that vertical source/sink distribution has a profound impact on scalar concentration profiles, fluxes, correlation coefficient, and scalar segregation.

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

Abstract 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 h...

Pheromone Movement in Four Stand Thinning Scenarios: High Frequency Plume Observations

An atmospheric tracer experiment using SF6 was designed to assess changes in the dispersive environment in the trunk space of a southern pine forest through four thinning regimes. The experimental plot was thinned from dense boles and thick understory (>140 ft2 (13 m2) basal area) in four stages with the final basal area being 70 ft2 (6.5 m2 ). Observations indicate that thinned stands are less susceptible to bark beetle attack and one possible reason could be that the plumes of pheromone the insects use for signaling cannot achieve the intended purpose in the thinned stand. The pheromone mechanism could be altered through direct dilution of the gaseous plume, through a reduction in spatial coherence of a plume making it more difficult to follow back to a source or through loss of the plume vertically from the stand environment through lofting due to surface heating and loss of overhead containment. This work is part of a larger program to improve the success of forest insect management strategies using pheromone. Data analysis is on-going but the high frequency tracer plumes examined in this study show that the plumes are more dilute and much less coherent spatially in the thinned stands. The plumes are filamentous in nature in all cases but wander (whip) across a larger volume of space in the thinned stands.

Large Eddy Simulation of Near-Field Dispersion Within and Above Forest Canopies

Numerical simulations were conducted to investigate the feasibility of predicting near field concentrations of a tracer gas within and above forest canopies. The current research is geared towards providing forest managers with a tool for developing anti-aggregation techniques to control the bark beetle. Several field experiments have been conducted in different forest canopies linking tracer gas concentration fields with meteorological and canopy parameters. Field experiment results are site and situation specific. Numerical simulations are far less expensive and allow for variation in virtually all flow parameters such as atmospheric stability, wind speed and direction, and turbulence intensity. As a first step, a CFD simulation has been used to study dispersion in a generic lodgepole pine forest canopy based on leaf area index (LAI) and stem density. Steady Reynolds Averaged Navier Stokes (RANS) solutions were computed using the k-e and Reynolds Stress Model (RSM) turbulence closure models. These solutions provide insight into in-canopy dispersion; however they do not fully capture the dynamics of the flow. The current work uses large eddy simulation (LES). LES resolves large flow dominated eddies while modeling smaller eddies using a sub grid scale model. Unsteady LES, can be used to capture the dynamics of flow within a canopy, including large rolling eddies above the canopy, bursting and sweeping within the canopy, multiple shear layers, and drainage flows.Copyright