FROM BALANCE OF NATURE TO HIERARCHICAL PATCH DYNAMICS - A PARADIGM SHIFT IN ECOLOGY

A common assumption historically in ecology is evident in the term Bal ance of nature. '' The phrase usually implies that undisturbed nature is ordered and harmonious, and that ecological systems return to a pre vious equilibrium after disturbances. The more recent concepts of poin t equilibrium and static stability, which characterize the classical e quilibrium paradigm in ecology, are traceable to the assumptions impli cit in ''balance of nature. '' The classical equilibrium view, however , has failed not only because equilibrium conditions are ran in nature , but also because of our part inability to incorporate heterogeneity and scale multiplicity into our quantitative expressions for stability . The theories and models built around these equilibrium and stability principles have misrepresented the foundations of resource management , nature conservation, and environmental protection. In this paper, we synthesize recent developments that advance our understandings of equ ilibrium vs. nonequilibrium, homogeneity vs. heterogeneity, determinis m vs. stochasticity, and single-scale phenomenon vs. hierarchical link ages in ecological systems. The integration of patch dynamics with hie rarchy theory has led to new perspectives in spatial and temporal dyna mics, with explicit linkage between scale and heterogeneity. The major elements of the hierarchical patch dynamics paradigm include the idea of nested hierarchies of patch mosaics, ecosystem dynamics as a compo site of patch changes in time and space, the pattern-process-scale per spective, the nonequilibrium perspective, and the concepts of incorpor ation and metastability. Both environmental stochacticities and biotic feedback interactions can cause instability and contribute to the dyn amics observed at various scales. Stabilizing mechanisms that dampen t hese destabilizing forces include spatial incorporation, environmental disturbances, biological compensatory mechanisms, and heterogeneity a bsorption. Hierarchical patch dynamics incorporates certain ''emergent properties'' of ecological systems, such as metastability or persiste nce at the meta-scale, as opposed to the transient dynamics that usual ly characterize local phenomena. In contrast to the stability that der ives from an assumed self-regulation in a closed system, the concepts of incorporation and metastability deal explicitly with multiple-scale processes and the consequences of heterogeneity. The mob important co ntribution of hierarchical patch dynamics lies in the framework provid ed for explicitly incorporating heterogeneity and scale, and for integ rating equilibrium, multiple equilibrium, and nonequilibrium perspecti ves.