Entropy in Landscape Ecology

Dear Colleagues,

Entropy and the second law of thermodynamics are the central organizing principles of nature. However, 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. Descriptions of landscape patterns, processes of landscape change, and 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 pioneering works in the field of landscape ecology, yet, in subsequent decades, our field has largely failed to embrace and utilize these relationships and constraints, with a few exceptions. The purpose of this Special Issue in Entropy is to bring together the best scientists across the world, who are working on applications of thermodynamics in landscape ecology, to consolidate current knowledge and identify key areas for future research. A recent editorial in Landscape Ecology on thermodynamics in landscape ecology identified the following topics as deserving particular focus for future work, and we hope the Entropy Special Issue will address many of these in depth.

1) There is a critical need to define the configurational entropy of landscape mosaics as a benchmark and measuring stick, which subsequently can be used to quantify entropy changes in landscape dynamics and the interactions of patterns and processes across scales of space and time.

2) The second law and entropy are of direct relevance to landscape dynamics as all changes in nature result in increases in system disorder and reduction in free energy of the closed system. Therefore, landscape time series data record this process. In a closed system, all time series will show increasing disorder and reduction in free energy over time, but ecological systems are open systems, and thus time series may show dynamic patterns without directional changes in disorder or free energy.

3) Ecological systems are driven by continual inflow of energy from the sun, and are not thermodynamically closed systems. This inflow of energy enables biological processes to function, driving photosynthesis “uphill” against the current of entropy, with ecological food webs then providing a “cascade” back down the free energy ladder, reducing free energy and increasing thermodynamic disorder. Landscape ecologists should more formally associate landscape dynamics with changes in entropy and quantify the function of ecological dissipative structures.

4) Observing a dynamic equilibrium in a landscape does not imply absence of increasing entropy. Just as an organism maintains homeostasis by functioning as a dissipative structure consuming and degrading high free energy organic molecules and releasing heat and highly oxidized metabolic products, a landscape maintains a dynamic equilibrium under a disturbance-succession regime through the collective emergent property of many organismal dissipative structures in interaction with abiotic drivers, such as solar energy, temperature, and moisture.

5) In forest systems, the dynamics range from gap-phase replacement of individual trees as windfall and senescence occurs to large-scale patterns of patch dynamics in response to wild fire and other large contagious disturbances. In each of these there is a dynamic equilibrium of landscape patterns, with different kinds of heterogeneity at different scales. In neither is there any trend to decrease in macrostructural stage, but rather a characteristic range of variation in landscape structure over time (e.g., change in macrostate within a characteristic range), as a function of the nature of the disturbance-succession process in that system. Linking the scale dependence of landscape dynamics to thermodynamic constraints across different ecosystem types would be central to generalizing the application of entropy in landscape ecology.

6) The linkage of the second law of thermodynamics and the entropy principle with the concepts of resistance, resilience and recovery seems important, as is linkage to ideas of dynamic equilibrium and dissipative structures.

7) There are more ways to be broken than to be fixed, more ways to be dead than alive, more ways to be disordered than to be ordered, and thus thermodynamic changes always lead to less predictability in the future state than the current state. All increases in entropy result in increasing disorder and lower potential energy in the closed system. This by definition decreases predictability, as there are more ways to be disordered than ordered and more ways to have dissipated energy than ‘‘concentrated’’ energy. This is always the case, and increase in entropy always leads to decrease in predictability in the closed system. However, landscapes are open stems and understanding the flow of energy and resulting patterns of order and disorder may result in increase or decrease in system predictability over time depending on whether the energy flow results in net decrease in entropy of the landscape or a net increase.

8) Fractal dimension seems directly related to entropy. Fractal dimension is a measure of a pattern-process scaling law and the relationships of such scaling laws to the thermodynamics of dissipative structures is a topic that should be explored. One may conjecture that the reason there are fractal scaling laws at all is because of the thermodynamic behavior of dissipative structures.

9) The scale challenges in landscape ecology are not a source of “departure” from thermodynamics, but rather are products of the action of dissipative structures organized across a range of scales or hierarchical levels. Attention should be given to entropy, complexity theory and the organization of ecological systems as a multilevel or multi-scale system of dissipative structures.

10) Thermodynamic irreversibility is a fundamental attribute of the universe and all things in it, including landscapes. If landscapes appear to not follow irreversibility laws then it is an indication of an insufficiency of how landscape ecological analysis reflects the reality of the universe. When ecological systems are properly viewed as multiscale and hierarchically organized dissipative structures then it is clear that thermodynamic irreversibility does apply.

11) The application of thermodynamic entropy concepts in landscape ecology has not addressed the true thermodynamic nature of the actions of dissipative structures across scales, and this has been limited by failure to measure energy transformations, changes in free energy, changes in configurational entropy of landscape mosaics. As a result, there has been a nebulous and inconsistent application and interpretation of these ideas in the field.

Prof. Dr. Samuel A. Cushman
Guest Editor

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• Entropy in Landscape Ecology II in Entropy (7 articles)
• Entropy in Landscape Ecology III in Entropy (3 articles)