With the reopening of Yosemite National Park, thousands of tourists are eagerly returning to enjoy the spring splendor. But few are aware that all is not well in this spectacular ecosystem -- or that they can help to learn why.

High in the snow packed meadows above Half Dome, researchers have found serious declines in most of the amphibian populations, which are sensitive indicators of environmental change.

With the aid of the University of California Research Expeditions Program, Walt Sadinski of UCSF will lead three teams of volunteers this summer to investigate what is causing the decline. Three sessions run from June 7 through July 20. Cost is $1,095.

In another of the UREP environmental programs, Berkeley faculty members Ignacio Chapela and Laurie Osher with the College of Natural Resources will explore the forests and fungi of Ecuador in part to determine if commercial mushroom growing can improve the local community's economic stability.

It turns out production of mushrooms grown in pine forest plantations on the lower slopes of two extinct volcanoes is 1,000 times greater than typical mushroom production. The expedition will run from July 26 through Aug. 9. The cost is $1,285, with the group assembling in Quito, Ecuador.

These projects are among more than a dozen environmentally oriented research projects in which members of the public join UC researchers and scientists.

Expeditions are offered around the globe.

In all UREP expeditions, volunteers join professional researchers and provide support for the work by paying the cost of their own meals and lodging, ground transportation and research equipment.

The contributions qualify as tax-deductible charitable donations.