Previously, various attempts have been made to present an ecosystem theory that could be applied to quantitatively explain ecosystem processes and their responses to disturbance and changing impacts. While we cannot cover all the attempts here, we focus on those based on systems perspectives and thermodynamics.
One of the early pioneers in Systems Ecology, Ken Watt, proposed his theory in the important work Ecology and resource management in 1968, which opened the way for greater systems thinking in ecology. In the 1970s B.C. Patten edited four volumes with the title Systems Analysis and Simulation in Ecology. These four volumes gave the state-of-the-art of systems ecology at that time and was a useful reference in systems ecology. All the volumes formed in a sense an early attempt to develop an ecosystem theory. During the 1980s a number of scientists contributed to an ecosystem theory: H.T. Odum, R. Ulanowicz, B.C. Patten, R. Margalef, and S.E. Jorgensen to mention a few. For example, H.T. Odum's book from this period, Systems Ecology: An Introduction, is probably one of the best attempts to make a comprehensive ecosystem theory. The discussion of hierarchy theory, allometry, and scaling problems in the 1980s should also be mentioned. T.F.H. Allen and T.B. Starr in their book Hierarchy, Perspectives for Ecological Complexity (1982) and R. O'Neill, D.L. De Angelis, J.B. Waide, and T.F.H. Allen in the book A Hierarchical Concept of Ecosystems (1986) presented hierarchy theory and made it an almost fully accepted part of ecosystem theory already 20 years ago. Peters (1983) publication of many allometric principles should also be mentioned in this context. Polunin (1986) edited a book titled Ecosystem Theory and Application, which was an early attempt to apply ecological theory to address some of the global environmental issues of the day. The 1980s and early 1990s saw a lot of interest in the Stream Ecosystem Theory (e.g. Cummins et al., 1984; Minshall et al., 1985; Minshall, 1988; Wiley et al., 1990) which focused on streams as open systems, controlled primarily by their allochthonous riparian input.
In 1992, S.E. Jorgensen gave an overview of these contributions in his book Integration of Ecosystem Theories: A Pattern. The various contributions to an ecosystem theory were very different, but a closer study of the proposed theories revealed that they actually were different angles and covering different aspects, but largely were consistent, complementary, and formed as the title of the book indicates a pattern. H.T. Odum's theoretical contributions to systems ecology were summarized by C.A.S. Hall (1995) in the book Maximum Power—the Ideas and Applications of H.T. Odum. R. Margalef's (1997) book Our Biosphere summarized his contributions to systems ecology. It was based on a well-balanced cocktail of thermodynamics and ecology. Macroecology by J.H. Brown (1995) presents from this period a quantitative ecological attempt to explain particularly bio-geophaphical observations and Reynolds (1997) expands his ideas on theory describing aquatic habitats.
Patten and Jorgensen (1995) edited the book Complex Ecology—The Part-Whole Relation in Ecosystems in which 31 systems ecologists contributed, presenting a wide overview of many different approaches and viewpoints, from quantum mechanic considerations (see herein, Chapter 3), to modeling theory, to network theory (Chapter 5), to feedback mechanisms (Chapters 4 and 7), to cybernetics (Chapters 4 and 7), and thermo-dynamics (Chapters 2 and 6). Furthermore, Jorgensen, Patten, and Straskraba have published a series of papers in the journal Ecological Modelling under the title "Ecosystems Emerging". The paper subtitles to date are: (1) Introduction, (2) Conservation, (3) Dissipation, (4) Openness, and (5) Growth. The remaining papers include: (6) Constraints, (7) Differentiation, (8) Adaptation, (9) Coherence, and (10) Applications. Similar to this book, these papers are rooted in thermodynamic laws and basic properties of ecosystems.
Coming from a more biogeochemical perspective, Agren and Bosatta (1996) published Theoretical Ecosystem Ecology—Understanding Element Cycles, which put emphasis on the importance of carbon and nitrogen cycling in ecosystems and is a commonly used textbook in this field.
In 2001, Jorgensen and Marques published "Thermodynamics and systems theory, case studies from hydrobiology" (Hydrobiologia, 445: 1-10). The paper claimed that we could develop ecosystem laws and apply them similarly to the application of physical laws in physics. Similarly, the December 2002 issue of the journal Ecological Modelling (158: 3) was based on nine papers by different authors invited to show that we could explain theoretically many papers published in ecology, which themselves were presented as observations or rules without any theoretical basis. The nine papers showed successfully that it is possible to explain theoretically much more in ecology than is generally presumed.
In 2004, Jorgensen and Svirezhev published Towards a Thermodynamic Theory for Ecosystems. The book covers a major part of the ecosystem theory because thermodynamics is the foundation for understanding many ecosystem processes. Thermodynamics is, however, a difficult scientific discipline to understand, which unfortunately prevents wider application. The presented theory is, however, coherent and is able to explain many ecological observations.
To claim that we have laws providing precise predictive capacity is a simplification in the sense that ecosystem laws inevitably will be different from physical laws due to the complexity of ecosystems compared with physical systems. Expressed differently, it will be much harder to formulate causality in ecology than in physics, but there seems no doubt that ecosystems have some general properties that can be applied to make predictions and understand ecosystems' response to perturbations. The focus has, therefore, in this book been on general processes, properties, and patterns.
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