Vernal pools have been a real sore spot between ranchers and environmentalists in recent years, but it turns out there may be more common ground there than either group realizes. These shallow, ephemeral ponds scattered throughout much of the state's low-lying rangeland put on a colorful display of native wildflowers each spring and are home to several species of threatened and endangered fairy shrimp. One of the biggest threats to vernal pools -- apart from urban development -- is invasion by exotic weeds such as medussahead, perennial ryegrass and devil's claw. These unwelcome invaders, if left unchecked, will choke out native plants such as meadowfoam, tidy tips and downingia. Recently published research by Sheila Barry, UC livestock and natural resources advisor for the northern Sacramento Valley, shows that grazing is the key factor keeping these delicate ecosystems in balance. Barry's peer-reviewed research was published last fall in Rangelands, a journal for scientists and managers of grazing lands. She has also prepared a four-color leaflet, "Rangeland Oasis," that describes the biodiversity and ecology of vernal pools and the role of livestock grazing in them.