In 1996, The Nature Conservancy adopted Conservation by Design: A Framework for Mission Success. TNC’s goal at that time was “the long-term survival of all viable native species and communities through the design and conservation of portfolios of sites within ecoregions.” From the late 1990s through the late 2000s, TNC developed “portfolios” of conservation areas in 68 U.S. ecoregions.
TNC’s total U.S. ecoregional portfolio includes 8,261 conservation areas.
Site sizes ranged from less than 1 acre (e.g. Jerry Smith Farm Park near Kansas City) to over 12.0 million acres (Sandhills Prairie in Nebraska); the next largest site was Crown of the Continent at ~4.3 million acres. Sandhills Prairie site was excluded from the Last Great Places analysis as an outlier, in that 11 other large sites – several individually larger than 100,000 acres – were contained within the Sandhills Prairie “megasite.”
TNC’s portfolio, excluding Sandhills Prairie, totaled 618,138,530 acres. Approximately 1% of the TNC sites comprise approximately 23% of the total TNCs area. 571 sites were smaller than 1 sq. km (247 acres).
Click here for links to ecoregional plans in the eastern U.S. or here for links to ecoregional assessments for the southwest U.S. Other ecoregional plans can be found by search on TNC’s Conservation Gateway.
Several TNC ecoregions extend across the U.S. borders; cross-border sites were included in the assessment of America’s Last Great Places if their center fell in the United States.
The evaluation factors to select Last Great Places were analyzed for 4,122 TNC sites over 10,000 acres.