© The Nature Conservancy
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The biodiversity of the Great Plains evolved under three dominant, large-scale ecological processes: fire, grazing and climate. Over the past 150 years, however, the conversion of the Plains landscape for agriculture has resulted in a reduction in the areal extent of natural ecological systems (largely prairie) and a loss or significant reduction numbers of many associated species. Relatively few prairie systems of sufficient size remain within the region to maintain the full array of historic ecological processes and species interactions.
As a means of tracking the loss of natural landscapes in the Plains and assessing the potential for maintaining the biodiversity of the region over the long term, landscape-scale areas (> 38 km?) with largely intact natural or semi-natural vegetation were identified through an interpretation of early 1990's Landsat Thematic Mapper (TM) satellite imagery. Landsat TM scenes were visually interpreted to delineate untilled landscape-scale areas, with landscape areas subsequently digitized and assembled into a GIS data layer for use in ecoregional conservation planning.
It is within these largely intact natural landscapes that the historic suite of ecological processes (regional to local scale) still likely operate (or can be restored) at or near their natural scale, and provide the basis for long-term viability of most native species occurring in the region. Because of this role, landscapes have been used as the principle framework for constructing ecoregional conservation plans. Analyses of completed ecoregional conservation plans of four Plains ecoregions have clearly illustrated that landscapes (as potential conservation areas) capture an inordinately large percentage of species and communities of conservation concern. As a result, most sites deemed to be of highest conservation priority in these ecoregions are large, relatively intact landscapes.
Analyses of this landscape coverage shows that approximately 33% of the historic natural vegetation of the Plains region still remains within landscape-scale areas. These large landscapes, however, are not uniformly distributed across the Plains: 52% of the total area of shortgrass ecoregions still falls within landscapes, 39% of mixed-grass, 9% of tallgrass, 40% of Acacia-Shrub Savanna, and 85% of Black Hills. This regional pattern illustrates a precipitous decline from west to east that reflects the arability of the region.
||Brian Schreurs, Jonathan Haferman