Like humans cooling themselves through sweat, trees regulate temperature through a process called transpiration. The once-majestic oak tree is all but dead: battered by repeated heat waves, it has shut down vital functions to conserve water and is slowly dying in a French forest. It is one of countless trees across Europe's forests adopting drastic—and often fatal—strategies to survive worsening heat and drought linked to climate change. As France endures a record-breaking early season heat wave, scientists warn that many of Europe's forests are already bearing the scars of years of rising temperatures and intense drought. Like humans cooling themselves through sweat, trees regulate temperature through transpiration, drawing water from the soil and releasing it as vapor through tiny pores in their leaves. As temperatures rise, water loss from leaves and soils accelerates, forcing trees into dire straits to conserve moisture.…