The number of dead trees in California’s drought-stricken forests has risen dramatically to more than 102 million in what officials described as an unparalleled ecological disaster that heightens the danger of massive wildfires and damaging erosion. Officials said they were alarmed by the increase in dead trees, which they estimated to have risen by 36 million since the government’s last survey in May. The U.S. Forest Service, which performs such surveys of forest land, said Friday that 62 million trees have died this year alone.