pine forests

Four years of too little water is killing millions of trees in the Sierra, yet some giant sequoias still thrive. Tree-climbing scientists are exploring sequoias branch by branch to find their secret.

Earth is home to more than 3 trillion trees, a new map of forest density shows. That's more than anyone realized. But the total is also down about 46 percent since the first humans arrived.

An expensive delicacy among nuts, pine nuts are foraged — not farmed — from distant forests. In some places, the delicate ecosystems that produce the nuts are disappearing.