“The oak tree and me,” said Carl Sagan, “we’re made of the same stuff.” Sagan’s work was focused on the cosmos, but he understood that here on earth, the lives of animals and plants are as intertwined as strands of the double helix. The artist Giuseppe Penone expresses much the same belief in his sculptures. A year-long installation of two monumental Penone cast-bronze trees—Ideas of Stone (2004) and The Logic of the Vegetal (2012)—graces Fort Mason, the historic site within Golden Gate National Recreation area in San Francisco. —L.J.