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Stability (some prefer to use ‘constancy’) is often invoked by those interested inestablishing whether conditions will remain steady or will return via a predictable pathto something similar to the initial steady state after disturbance. It is widely held thatecosystem stability is related to biological diversity: the greater the variety of organismsthere is, the less likely there is to be change in biomass production, althoughpopulation fluctuations of various species may still occur (Tilman, 1996). However, itis quite possible that a change in some parameter could have an effect on all organisms.Thus, diversity may help ensure stability, but does not guarantee it. An ecosystemmay not have become stabilised when disturbed: it may be close to a starting point, orit could be undergoing cyclic, more or less constant or erratic change. An ecosystemmay return to stability after several disturbances but fail to return after a subsequentupset for various reasons (Holling, 1973). Some ecosystems are in constant non-equilibriumor frequent flux, rather than in a stable state at or near carrying capacity. Returnto a pre-disturbance state is therefore uncertain.Resilience is displayed by many things; for example: organisms, ecosystems,communities, regions, individuals, societies, institutions, and nations. Resilience maybe defined in many ways:● The ability to return to maintain a steady-state ecosystem.● The facilitation of adaptive behaviour.● The speed of recovery of a disturbed ecosystem.● The number of times a recovery may occur if disturbance is repeated.The concept of resilience has been applied by human ecologists: some societiesabsorb or resist social change and continue with traditional skills and land uses ordevelop satisfactory new ones; other societies fail, and their resource use and livelihoodstrategies degenerate. In humans, resilience and vulnerability are not fixed or predetermined;they vary as a consequence of environmental factors, institutions, attitudes,innovation and so on. In particular, poverty can make people more vulnerable and lessresilient.Referring to sensitivity and resilience, Blaikie and Brookfield (1987: 11) suggesteda simple classification of land, which may be modified to apply to ecosystems in general:1 Ecosystems of low sensitivity and high resilience – These suffer degradation onlyunder conditions of poor management or natural catastrophe. Generally these arethe best ecosystems to stretch to improve production of food or other commodities.2 Ecosystems of high sensitivity and high resilience – These suffer degradation easilybut respond well to management and rehabilitation efforts.3 Ecosystems of low sensitivity and low resilience – These initially resist degradationbut, once a threshold is passed, it is difficult for any management and restoration
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