News Item from David Tilley for ISAER Newsletter, managed by Enrique Ortega. July 28, 2012


David Tilley’s Ecosystem Engineering Design Lab at the University of Maryland has been busy the last few years developing new talent and knowledge on the theoretical basis and methodological practicalities of emergy synthesis.

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Post-Grade Students

Elliott Campbell, Amy Hudson and Brandon Winfrey are all completing their graduate degrees in Environmental Science and Technology in 2012. Each has been working on novel aspects of emergy synthesis as described below.

Elliott Campbell successfully defended his Ph.D. dissertation, “Valuing forest ecosystem services in Maryland and suggesting fair payment using the principles of systems ecology,” on July 23rd, 2012. Realizing that forests provide a multitude of vital benefits, like regulating atmospheric gas exchange, ameliorating micro-climates, stabilizing coastlines and riverbanks, providing wildlife habitat, generating and maintain soils, improving water quality, dampening storm flows, abating air pollution, and providing food, fiber, fuel and shelter to the ecosystems, economies and people of all over the world, Dr. Campbell’s research proposed that an Ecological Investment Corporation (EIC) could be a tool for society to direct payments from consumers of ecosystem services to land stewards to encourage the production of ecosystem services. Emergy synthesis was used to determine (1) the value that forest ecosystem services provided to Maryland’s economy, society and environment (i.e., public value) and (2) a fair price that should be paid to land stewards for producing specific ecosystem services (i.e., fair payment price). Public value was based on the overall contribution that a flow of primary emergy (e.g., a natural resource) makes to the state economic product. A fair payment price was the dollar value that society should pay land stewards for producing ecosystem services.  Dr. Campbell found that Maryland’s land stewards of forest should receive compensation in the range of $178 to $744 million per year. He also found that the average resident of Maryland enjoys $850 worth of ecosystem services as public value.  On an area basis, the typical acre (0.4 hectare) generates over $2000 of ecosystem services as public value. A land steward should receive a fair payment price of $71 to $298 per year per acre. Other highlights of his dissertation included novel methods of modeling biodiversity using emergy including a latitudinal study of biodiversity and emergy along eastern North America, assessment of an emergy ecological network analysis to calculate transformities along a forest food web, and quantification of the historical accumulation of ecological debt in Maryland. Soon his research will be available at or email

Amy Hudson is finishing up her Masters thesis entitled “Assessing the uncertainty of emergy analyses with Monte Carlo simulations.” Her research is concerned with how to obtain and reduce levels of uncertainty in emergy evaluations and unit emergy values (UEV’s, e.g., solar transformity). Specifically, she has used crop production systems as a model system to investigate where uncertainty originates in emergy evaluations and how it is propagated through UEV’s. She collected data from published studies to generate input and output UEV’s for various Monte Carlo simulations that assumed either normal, uniform or log-normal random distributions. A sensitivity analysis was performed for each input to determine the input’s individual influence on the output UEV. For the crop systems, she found that nitrogen fertilizer and soil erosion, which were two inputs with the greatest emergy contribution, also had the largest impact on uncertainty of the output transformity. Her study should provide insight on how to assess uncertainty in an emergy evaluation to perform statistical tests of significance on the results.

Brandon Winfrey is working to complete his dissertation in 2010. It is tentatively entitled, “Material and Emergy Cycling in Natural and Human-Dominated Systems.” His research is focused on improving emergy accounting methods for systems with significant amounts of cycling. Specifically, he is investigating: 1) the development of new emergy methods for evaluating the sustainability and technological appropriateness of ecologically engineered systems, like treatment wetlands, which provide society with ingenious ways to recycle concentrated and dilute co-products; and 2) dynamic emergy models for improving the theoretical basis and methods for assessing the cycling of emergy and materials in natural and human-dominated systems. Better modeling of the emergy associated with conservative materials will improve the capability for accounting for emergy in systems with large amounts of recycling. On Brandon’s earliest achievements was the development of a new emergy index. The Treatment Sustainability Index, the ratio of renewable, environmental and net wastewater to the purchased and environmental loading inputs, was developed to rate the sustainability of ecologically engineered systems, like treatment wetlands.

Recent Publications

A.R. Clewell, J. Aronson, David R. Tilley. Ecological Restoration: Principles, Values, and Structure of An Emerging Profession (2007) Island Press, Washington, DC 216 pp., Paperback (also available in hard cover), Price: $30, ISBN: 978-1-59726-169-2. Ecological Engineering, Volume 34, Issue 2, 2 September 2008, Pages 187-189.

David R. Tilley. Dynamic accounting of emergy cycling. Ecological Modelling, Volume 222, Issues 20–22, October–November 2011, Pages 3734-3742.

Paolo Vassallo, Chiara Paoli, David R. Tilley, Mauro Fabiano. Energy and resource basis of an Italian coastal resort region integrated using emergy synthesis. Journal of Environmental Management, Volume 91, Issue 1, October 2009, Pages 277-289.

David R. Tilley, Mark T. Brown. Wetland networks for stormwater management in subtropical urban watersheds. Ecological Engineering, Volume 10, Issue 2, 15 June 1998, Pages 131-158.

Erika Felix, David R. Tilley, Gary Felton, Eric Flamino. Biomass production of hybrid poplar (Populus sp.) grown on deep-trenched municipal biosolids. Ecological Engineering, Volume 33, Issue 1, 1 May 2008, Pages 8-14.

Erika Felix, David R. Tilley. Integrated energy, environmental and financial analysis of ethanol production from cellulosic switchgrass. Energy, Volume 34, Issue 4, April 2009, Pages 410-436.