Mediterranean ecosystems

On disturbance I diversity ¬°functioning It has been well documented that disturbance, at a moderate level, can promote diversity. In the Mediterranean basin, human-induced landscape variation - fields, pastures, scrublands and forests -- leads to high diversity at all levels as well as to multiple services to humankind. Even complex manipulation of ecosystems, such as in the "dehesa" agro-ecosystem in southern Spain, has provided a diversity of organisms and services and has been sustainable, at least until recently. Contrast this with the recent dramatic massive conversion of the native vegetation of western Australia to wheat fields, resulting in large alterations of ecosystem functioning, particularly related to water balance. This conversion has resulted in salinization of soils and losses of many services, including nutrient supply, and pest and erosion control. There are now efforts to repair the damage by reintroducing perennial systems. In the Mediterranean case, in a sense, there has been adaptive management practices through the centuries - with any management experiment being small-scale because of the lack of the mechanical means to do otherwise, as well as the complex land tenure system which also led to small-scale, and patchy, alterations. In western Australia the recent development of this region was rapid and extensive, aided by fully mechanized conversion of vast areas. By the time the problems were recognized, extensive damage had already been done.

The lesson is that even in a world that is increasingly impacted by human activities, we can manage landscapes to produce sustainable ecosystems that provide ample services, but there is a considerable challenge in doing so. The examples are there: we need to learn from them.

17.3.2 The open ocean

Managing in the dark We lack details on the ecological structure and function of the open-ocean ecosystem, and for good reasons. This system is vast and difficult to study. We are only now learning of the rich diversity of the benthic system. In general, we have very little understanding of the interactions of the components of the open oceans. This lack of knowledge has put us all at peril, as evidenced by the sudden and dramatic decline of the oceans fisheries. The drivers of this demise are no doubt complex, but most certainly includes the overfishing made possible by "industrial" harvesting. There is little understanding of the ecosystem consequences of the demise of specific fisheries, since research has generally been more commodity-based (a particular fish) rather than system-based. It could be that total ocean productivity has not declined, but that there has only been a shift in the abundances of various species. We do not know. It is stated in this volume that there may not be as much functional equivalency in the oceans as there is on the land, and thus the possibilities for functional replacement are low, for functions other than production. This is an important proposition that needs further study. We are already seeing a great interest in a new approach to fisheries management. It is quite clear that this new approach will, for the first time, be imbedded in an ecosystem paradigm, where functions and services are considered, and where humans are considered an increasingly dominant element in this ecosystem.

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