Thursday, January 27, 2011

Press-Pulse Dynamics: A Hypothetical Feedback Model for Long-Term Social-Ecological Research

An important conceptual resource for BES III has recently appeared online. This publication presents the feedback cycle between social and ecological structures and functions as mediated by ecosystem services and by press and pulse events.

This conceptual framework highlights that the dynamics of press and pulse events is a key link in the integration of social and bioecological processes and structures. A version of the feedback cycle adopted for BES III, and identified by its older label of the Integrated Science for Society and Environment (ISSE) appears as Figure 2 in the BES proposal and in an earlier post on the Web Log. This framework is perhaps really best described as a model template, which can guide construction of more specific, testable models and hypotheses. This paper deserves serious study by researchers and scholars affiliated with BES.

The publication appears in the Ecological Society of America's journal, Frontiers in Ecology and Environment. Members of the Society and persons at subscribing institutions can find the paper through this Digital Object Identifier: doi:10.1890/100068

The full citation of the online publication is as follows:
Scott L Collins, Stephen R Carpenter, Scott M Swinton, Daniel E Orenstein, Daniel L Childers, Ted L Gragson, Nancy B Grimm, J Morgan Grove, Sharon L Harlan, Jason P Kaye, Alan K Knapp, Gary P Kofinas, John J Magnuson, William H McDowell, John M Melack, Laura A Ogden, G Philip Robertson, Melinda D Smith, and Ali C Whitmer. 2010. An integrated conceptual framework for long-term social–ecological research. Frontiers in Ecology and the Environment (e-View)

A key phrase from the abstract of this article is, "Here, we present an iterative framework, “Press–Pulse Dynamics” (PPD), that integrates the biophysical and social sciences through an understanding of how human behaviors affect “press” and “pulse” dynamics and ecosystem processes. Such dynamics and processes, in turn, influence ecosystem services – thereby altering human behaviors and initiating feedbacks that impact the original dynamics and processes."

Photo courtesy of University of Maryland, Baltimore County. View from the roof of the Administration Building toward downtown Baltimore.

Tuesday, January 25, 2011

Resilience: Ecology, Evolution, and Engineering

The concept of resilience is key to BES III. This powerful concept is ideal for understanding and working with complex, human ecosystems. However, it is the object of some confusion because there are two contrasting ways to frame and theorize the concept.

Originally, engineering and physical systems were the source of the concept as applied in ecology. Under the equilibrium paradigm predominant at the time, resilience was conceived of as the ability of a system to absorb a shock or deformation and to return to its original, or equilibrium, state. A rubber band is a perfect example of such a system. The loose, floppy form can be stretched repeatedly, and still return to its general band-like shape.

Engineering or equilibrium resilience is the concept used to describe this dynamic. This sort of resilience can be called engineering resilience because it characterizes built structures and infrastructure. Key to this idea is that there is an acceptable, desired, or equilibrium state of the system. Of course, extreme deformation or perhaps consistent strong deformation over time can lead to system failure. The band breaks when stretched too far, or after years of material degradation while encircling a thick wad of forgotten papers in a hot attic.

Equilibrium or engineering resilience may be of value when it is possible to identify a desirable state that is expected to persist over some specified time or at a particular spatial scale. But for many purposes, it is best considered a special case of the concept of resilience. A more inclusive concept suitable to systems that are not at equilibrium, or which are undergoing periodic or constant change is ecological or evolutionary resilience.

Ecological resilience does not ask whether a complex system returns to a previous or equilibrium state. Rather, it asks about the changes that a system can experience and still persist in the same dynamic form. Resilience is about the ability to receive shocks and still stay in the game. Systems that can adapt to change are said to be resilient. This then is an evolutionary kind of concept since adaptation is a central feature. This is in contrast to engineering resilience which is concerned with stability or permanence. So, ecological and evolutionary resilience are concerned with adaptive capacity and adjustment to change, not to return to a stable point. Rather than asking about the ability of a rubber band to return to its unstressed state, evolution asks about the rubber band becoming something else that is better adapted to the new conditions. It is of course silly to think about a simple, physical-chemical system such as a rubber band changing in such a radical way, but evolution, adaptation, learning, and adjustment are familiar capacities of biological and social systems. In other words, they are complex systems that can adapt. Resilience in the more evolutionary sense is the idea that points toward the question of how -- and how well -- a particular system can adapt to changing conditions or sudden shocks that come at unexpected times.

Changing concepts of resilience are relevant to the BES III main theme of Sanitary to Sustainable City. The sanitary city identifies a desired state, and seeks to keep structures or processes at that level. Given that societal and regulatory decisions identify legal or desirable targets for some features people must manage, a classical or engineering definition provides guidance about how to measure success. However, under changing environmental conditions, including social, economic, and environmental alterations, it may be more appropriate to ask about the capacity of the system to adjust to those changes. Recognizing that feedbacks among social, economic, and environmental factors and processes are an unavoidable part of urban ecosystems, this suggests that we learn how to go beyond the engineering resilience concept and understand and use the contemporary concept of ecological or evolutionary resilience.

Here are some references about this contrast and the nature of ecological resilience that are relevant to socio-ecological systems.

Gunderson, L. H. 2000. Ecological resilience - in theory and application. Annual Review of Ecology and Systematics 31:425-439.

Holling, C. S. 1996. Engineering resilience versus ecological resilience. Pages 31-44 in P. C. Schulze, editor. Engineering within ecological constraints. National Academies of Engineering, Washington, DC.

Thursday, January 20, 2011

BES Photo Album Now Publically Available

Need a photograph of BES research activities or sites for your teaching or non-commercial publication? Have a great photo of sites, people, research activities, or education in action? Access the BES Picasa album at to download photos.

If you use a photo, please credit Baltimore Ecosystem Study Long-Term Ecological Research project, and the National Science Foundation. You may use the photos to support academic, educational activities. The rights granted are non-exclusive and pertain to electronic and print formats.

If you have a photo to upload, please recognize that it may be used in the ways indicated above. Please provide a descriptive caption. We will assume that persons depicted give their permission to have their images used for educational and research purposes. Write to BES Information Manager, Jonathan Walsh through walshj at to obtain credentials to upload photos to this album.

Enjoy and contribute!