Thermodynamics in landscape ecology: the importance of integrating measurement and modeling of landscape entropy

Landscape Ecology, Nov 2014

Samuel A. Cushman

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Thermodynamics in landscape ecology: the importance of integrating measurement and modeling of landscape entropy

Samuel A. Cushman 0 0 S. A. Cushman (&) USDA Forest Service, Rocky Mountain Research Station , 2500 S Pine Knoll Dr., Flagstaff, AZ 86001 , USA - Entropy and the second law of thermodynamics are the central organizing principles of nature. Or perhaps more accurately, the second law is the central disorganizing principle. Hot things cool down. Cold things warm up. You cannot get something for nothing. You always pay more than you get. Things fall apart. You cannot repeat the past. We grow old and die. It is all downhill from here to the heat death of the universe. While at first these seem like grim and pessimistic ideas, a deeper understanding reveals that the disequilibrial processes of increasing entropy are what enables all organizing actions, such as the formation of a molecule, building of a cell, birth of a child, organization of an ecosystem. Yet strangely, the ideas and implications of the second law are poorly developed in the landscape ecology literature. This is particularly strange given the focus of landscape ecology on understanding pattern-process relationships across scales in space and time. Every interaction between entities leads to irreversible change which increases the entropy and decreases the free energy of the closed system in which they reside. This is the essence of the entropy principle. Descriptions of landscape patterns, processes of landscape change, propagation of pattern-process relationships across space and through time are all governed, constrained, and in large part directed by thermodynamics. This direct linkage to thermodynamics and entropy was noted in several of the pioneering works in the field of landscape ecology (e.g. Forman and Godron 1986; ONeill et al. 1986; Naveh 1987; Oneill et al. 1989). Yet in the subsequent decades our field has largely failed to embrace and utilize these relationships and constraints, with a few exceptions (see Wu and Loucks 1995; Zhang and Wu 2002; Zurlini et al. 2013). Landscape ecology sometimes has been criticized as a descriptive science focused on patterns without linkage to central organizing theories or principles. In recent decades this has been reversed in part with strong landscape ecology research focused directly on pattern-process relationships, drivers and responses across scales in space and time. Landscape ecology is the science of understanding the interactions of patterns and processes across scales. The second law of thermodynamics and the entropy principle provide a theoretical context which could help clarify and unify a large portion of landscape ecology research, and connect it to fundamental principles. In a review paper published in this issue Vranken et al. (2014) present an overview of the use of entropy in landscape ecology. They identified three main uses of the entropy concept in past landscape ecology research, including: spatial heterogeneity, unpredictability of pattern dynamics, and pattern dependence on scale. They conclude from their review that thermodynamic interpretations of spatial heterogeneity in the literature are not relevant, that thermodynamic interpretations related to scale dependence are highly questionable, and that of all applications of entropy in landscape ecology only unpredictability could be thermodynamically relevant if appropriate measurements were performed to test it. They note that while entropy is frequently mentioned in landscape ecology literature, it is rarely formally addressed and usually only applied in imprecise and descriptive terms. They note frequent contradictions in the interpretation of entropy in landscape ecology literature. The Vranken et al. (2014) review, in my opinion, shows how poorly the universally important topics of the second law of thermodynamics and the entropy principle have penetrated landscape ecology. There are many examples in the literature of informal linkage to the entropy concept, but virtually no formal, quantitative efforts to develop explicit theory derived from the second law. The review shows very few examples of the concepts even being mentioned (as a proportion of the literature) and virtually no formal, quantitative, theoretically justifiable application of thermodynamic ideas. They note that most authors addressing linkages between entropy and landscape patterns generally use the entropy principle metaphorically, referring to the linkage between entropy and landscape disorder, but not formally calculating it. Further they note contradictory interpretations of the conceptual linkage between entropy and landscape pattern. They note that no formal proposal for calculating the thermodynamic entropy of landscapes has been published and as a result conclude that any link between spatial heterogeneity and thermodynamic entropy should be treated with caution. This seems astounding for a field that has been so obsessed with measuring and interpreting landscape patterns has entirely neglected the fundamentally important and interesting (...truncated)


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Samuel A. Cushman. Thermodynamics in landscape ecology: the importance of integrating measurement and modeling of landscape entropy, Landscape Ecology, 2015, pp. 7-10, Volume 30, Issue 1, DOI: 10.1007/s10980-014-0108-x