Landscape Diversity

A landscape is "a mosaic of heterogeneous land forms, vegetation types, and land uses"

(Urban et al., 1987). Therefore, assemblages of different ecosystems (the physical habitats and the species that inhabit them, including humans) create the landscapes on earth. The scale of a landscape varies from about 100 square kilometers—about the size of a national park—to more than 1 million square kilome-ters—the size of a large physiographic region such as a river basin. Species composition and population viability are controlled by a landscape's structure (patch size and connectivity of habitats within the landscape; perimeter-area ratio) and function (nutrient cycling rates; hydrologic processes) (Noss, 1990). Certain animals and plants, including endangered species such as jaguars, wolves, and quetzals, range widely across several different ecosystems. Therefore, conservation management should be directed at whole landscapes to ensure that these species survive.

Landscape diversity depends on local and regional variations in environmental conditions, and the species supported by those environments. Landscapes are significantly affected by the activity of the species present. For example, although bacteria are some of the smallest organisms on earth, many species that live in rocks are thought to be important in the process of erosion, which shapes landscapes. The activity of modern humans has been one of the most significant factors affecting the appearance of landscapes in the past few thousand years, and substantially so in the past few centuries. More than half of all accessible surface freshwater is put to use (Vitousek et al., 1997). Industrial agriculture around the Aral Sea in the last thirty years has approximately halved that lake's surface area and depth, and tripled its salinity; and only two of Japan's 30,000 rivers are neither dammed nor modified (for references, see Harrison and Stiassny, 1999). Landscape diversity is often incorporated into descriptions of so-called ecoregions, which are geographically defined areas that integrate environmental conditions such as climate and geology, and support distinct assemblages of species and communities (Stein et al., 2000).

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