Our principal interest, approach and tool is systems ecology which we view as the application of integrative tools of science, including especially empirical data analysis and empirically-based simulation modeling, to the understanding and management of complex systems of nature and of people and nature. My principal focus throughout the diversity of projects I have undertaken in my life is, and always has been, the examination of how organisms and societies invest energy in resource exploitation, and how such investments change as the quality of resources changes. I have also studied the relation of energy use to various environmental issues including impacts of energy facilities on aquatic environments ands especially the relation between energy use and land use change to the global carbon budget. I have applied these approaches to small rivers, estuaries, fish migrations, tropical land use change, petroleum extraction, and the national economies of the United States, Argentina and Costa Rica.

        Most recently my interests have shifted toward integrative geographical modeling of environments and economies, especially in the tropics. Finally I have been most interested in assessing what I perceive to be the flaws in how we do (neoclassical) economics. These flaws grow out of the peculiar situation where we consider economic systems (e.g. a city, a country or a development project) as requiring only social science to understand and regulate. In other words there is a general failure to consider real economic systems as biophysical systems, even as ecosystems, which require energy and materials (all derived from nature) for their operation. In addition to our critiques of neoclassical economics (seen most explicitly in our 2001 paper in BioScience) we have been developing a conceptual alternative that we call biophysical economics. How this is undertaken can be seen most clearly in our comprehensive biophysical study of the Costa Rica n economy (Hall 2000) and our newest book (Hall and LeClerc (eds) Making development work: a new role for science). I work with my wife Myrna Hall (she does the most work!) on examining and predicting how humans use land over time. We are applying these tools to many sites in the tropics but also the Catskills and perhaps Adirondacks of New York. Although I have been working increasingly in human dominated landscapes I continue my interests in natural ecosystems through the work of my graduate students who work in more or less natural ecosystems in small streams in upstate New York and in the Luquillo LTER tropical forest site in Puerto Rico. In my mind it is all systems ecology, and in all cases we are asking questions about energy.