The report, States of the Union: Ranking America's Biodiversity, offers a striking picture of where wild plants and animals are found, and how they are faring. Based on an analysis of more than 21,000 species, the report was prepared for The Nature Conservancy by NatureServe, a non-profit organization that is the leading source of scientific information about rare and endangered species and threatened ecosystems. Drawing on ongoing species inventories conducted by state natural heritage programs, the report ranks all 50 states and the District of Columbia on several key biological characteristics including diversity of species; distinctiveness of the flora and fauna (endemism); levels of rarity and risk; and species already lost to extinction.

"This report holds both hope and peril," said Steve McCormick, president of The Nature Conservancy. "As an important snapshot of the biological health of our nation, it shows the extraordinary richness of the flora and fauna across all 50 states. But it also serves as a stark reminder that too many of these species are at risk of vanishing forever."

The top-ranking states in each of the four categories are:

Dr. Bruce A. Stein, the author of the report and a senior scientist with NatureServe, said, "the report highlights the interplay between the nation's natural history and human history, and provides insights into the scale of the nation's conservation challenges and opportunities." He notes that areas with the greatest species diversity are found in the topographically and climatically diverse Southwest, with California (6,717 species) and Texas (6,273 species) leading the nation. This is due in part, he said, to the enormous size of these two states, their ecological complexity and their location along the country's southern border.

Risk patterns among states -- as reflected by the proportion of a state's species considered imperiled or vulnerable -- also highlight Hawaii (where 63% of species are at risk) and California (with 29% of species at risk). Secondary centers of rarity are found in several other western and southeastern states including Nevada (16%), Alabama (15%), Utah (15%) and Florida (14%).

McCormick noted that 12 states -- or almost a quarter of the country - have more than 10 percent of their species classified as rare or at risk of extinction.

"This demonstrates that we will never be successful at protecting biodiversity if we concentrate our conservation efforts in small patches here and there," McCormick said. "We must protect large landscapes and work collaboratively with a wide array of interests. That means working with federal, state and local governments as well as private property owners so that land is managed in a manner that helps, not hurts biodiversity."

Although extinctions have touched every state in the nation, the report shows that certain regions have lost disproportionate numbers of species. Stein notes that states with a large number of extinctions tend to have either high overall species numbers, an inherently fragile flora and fauna, or intense human alteration of the landscape. Hawaii has suffered the gravest losses, with 217 presumed or possibly extinct species. On the mainland, Alabama tops the list of extinction-prone states with 90 species, many of which existed in freshwater systems. Many of the state's waterways have been dammed, dredged, or diverted, leading to the loss of numerous snails, mussels and fishes. California ranks third in the nation with 53 extinctions. Stein said the intensive conversion of the state's land and waters for agriculture, urbanization and other uses has had a severe impact on the many rare and narrowly restricted species that have evolved in this ecologically unique state.

California, with 1,295 species endemic, or unique, to the state, leads the nation in this category, according to the report. This is a result of its large size and the complexity of natural habitats in the Golden State. Stein says Hawaii also stands out for the distinctiveness of its flora and fauna. Because of the island chain's extreme isolation, most plants and animals native to the archipelago are descended from a relatively few colonists.

The report also looked at species diversity broken down by species categories, which revealed distinctive, and at times strikingly different patterns.

Diversity: Top-Ranking States by Species Category

Diversity for plants and mammals is highest in the Southwest, where many of the states are large and have numerous specialized habitat types. In contrast, amphibians and freshwater fishes reach their highest levels of diversity in the southeastern United States. Indeed, with its combination of Appalachian highlands and humid coastal lowlands, this region is a global center for freshwater diversity. Bird and reptile diversity are more geographically mixed with both eastern and western states represented in the top tier. Texas, which straddles both east and west, leads all other states for both groups.

Risk: Top-Ranking States by Species Category

Risk rankings highlight the significance of Hawaii, which is tops for most taxonomic groups (with the major exception of amphibians, which do not naturally occur in Hawaii). Risk patterns for amphibians and freshwater fishes, however, display an interesting contrast to diversity patterns in those same groups. Whereas southeastern states have the most species, the highest percentage of rare and at-risk fishes and amphibians are found in western states. Arizona, for example, an arid state more commonly associated with cacti, ranks highest for at-risk freshwater fishes.

The Nature Conservancy works in all 50 states and throughout Latin America, the Caribbean and the Pacific to protect biodiversity. Conservancy scientists, using data from organizations like NatureServe, undertake a detailed planning process called ecoregional planning in which they identify threats to species and determine what conservation activities need to be undertaken to protect them. The Conservancy then works in partnership with communities, government, business and property owners to implement conservation strategies to protect species.

"Ecoregional planning and the protection of whole functional landscapes provide us with the ability to reduce the number of species at risk," McCormick said. "This will not be an easy task, but future generations will judge us on our ability to succeed."

The Nature Conservancy is a private, international, non-profit organization that preserves plants, animals and natural communities representing the diversity of life on Earth by protecting the lands and waters they need to survive. To date, the Conservancy and its more than one million members have been responsible for the protection of more than 12 million acres in the United States and have helped preserve more than 80 million acres in Latin America, the Caribbean, Asia and the Pacific. On the Web at http://www.nature.org/.