Experimental branch warming alters tall tree leaf phenology and acorn production

An increasing number of field experiments have been initiated worldwide to study simulated effects of global warming. To experimentally determine how tall, mature trees respond to warming, we developed a new technique that heated canopy-level branches with electric heating cables. Using a canopy crane, we attached electric cables to top canopy branches of tall, mature Quercus crispula Blume (18–20 m in height) trees; shoot temperature was elevated 5 °C above ambient. Branch warming extended the length of the growing season of canopy leaves by later leaf fall. Moreover, branch warming increased acorn production. Application of this technique should lead to a better understanding of how tall, mature trees respond to global warming.