Trees and entire forests worldwide are threatened by increasing climate extremes and ensuing insect infestations. As sessile organisms, trees cannot escape threatening environmental conditions and must adapt their metabolic processes to confront the threats. Crucially important for plants is the production of energy-rich sugar molecules (carbohydrates) by photosynthesis. These compounds serve as both energy sources and basic building blocks for all metabolic processes. During climate extremes such as prolonged drought or heat, photosynthesis is impaired and trees produce fewer carbohydrates because CO2 uptake declines and water is scarce. The demand for energy-rich sugars is then not met and plants have to rely on stored reserves to maintain vital metabolic processes. When reserves become depleted, plants may starve to death or become vulnerable to disease and insect attacks as the defense system fails.
