Region
United States
50
West (U.S.)
17
Tropics
9
Southern States
6
Northeastern States
5
Rocky Mountains
5
Developing countries
3
Europe
3
Africa, Sub-Saharan
2
Antarctica
2
British Columbia
2
Canada
2
Mexico
2
Middle East
2
Northwest, Pacific
2
Polar regions
2
Southwest, New
2
Southwestern States
2
Arctic regions
1
Arizona
1
Asia
1
Asia, Central
1
Australia
1
Balkan Peninsula
1
Belize
1
California
1
Colorado
1
Colorado Plateau
1
Fort Valley Experimental Forest (Ariz.)
1
Fraser Experimental Forest (Colo.)
1
Great Plains
1
Guadalupe Mountains (N.M. and Tex.)
1
Guatemala
1
Gulf Coast (U.S.)
1
Hawaii
1
High Plains (U.S.)
1
Japan
1
Latin America
1
Louisiana
1
Madrean Archipelago
1
Marsh-Billings-Rockefeller National Historical Park (Vt.)
1
Mediterranean Region
1
Mexican-American Border Region
1
Middle West
1
New Orleans
1
North America
1
Pacific Ocean
1
Persian Gulf States
1
Rocky Mountains Region
1
South Africa
1
more ...