Landscape diversity and productivity

A loose global network of free market economies is the backdrop against which much of today's science is being done. Utility of system components is therefore usually a strong motivation for conservation. In the case of biodiversity, landscapes which offer a stable mosaic of opportunity for human exploitation are considered desirable and worthy of conservation, in the Mediterranean basin, humans have for hundreds of years derived sustained benefit from functional attributes of ecosystems, and have been responsible for the maintenance of biodiversity for this reason. Blondel and Aronson (1995) refer to the long tradition of mixed agricultural production where rural communities historically combined cultivation with animal husbandry and the harvesting of products from natural forests in what the ancient Romans called the ager-saltus-siha (field-pasture-forest) system. These integrated systems relied on the diversity of terrains and climates which could support them. Such stable systems existed from the Middle Ages until the mid-18th century in southern France (Blondel and Aronson, 1995), and until more recently in southern Spain and Portugal as the "dehesa" or "montado"' systems (Joffre et al. 1988). The apparent stability and sustainability of these systems appears to have been linked to the ecological diversity they comprised. Nevertheless, specialized forms of land-used have become more common, and selected aspects of system productivity has altered landscapes quite radically. With regard to forest products particularly, these range from the selective elimination of deciduous oaks for charcoal used in the French glass-blowing industry prior to the 1789 revolution, to the decimation of forests for shipbuilding during Roman times (Thirgood 1981). Other landscape transformations have included clearing of littoral zones for cereal crops, with later conversion to vineyards, and more recently to the concrete of urban and suburban environments. In all these instances, biodiversity has been altered to manipulate system function in terms of productivity for human utility. What still needs to be assessed is: (i) the degree to which these transformations have affected the stability of those systems; (ii) to what extent input of energy is required for maintenance of the new system slates; (iii) what degree of degradation and loss of potential function has been incurred by changes in diversity; (iv) whether or not system shifts are reversible.

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