D:
Deserts - Information on the effects of global warming on deserts [Environmental Protection Agency (EPA)]

H:
Habitats - Resources related to Earth is host to desert, forest, marine, montane, prairie, tundra and wetland habitats, each of which supports its own specialized plant, animal, and microbial species assemblages. [Department of the Interior, U.S. Geological Survey (USGS), National Biological Information Infrastructure]

O:
Our dynamic desert landscape - Overview of studies of fragile and active landscape of the American Southwest deserts, including projects on geologic mapping, surface processes, remote sensing research, ecological processes, and earthquake hazard applications. [Department of the Interior, U.S. Geological Survey (USGS), Geologic Division, Western Region Earth Surface Processes Team]