The timing of leaf damage affects future herbivory in mountain sagebrush (Artemisia tridentata).

Many plants respond to herbivory by increasing expression of defensive traits. The defensive response of plants can vary depending on plant condition, seasonality, and time of day. Due to a lack of field-based studies, it is unclear how temporal variability in defensive response may alter future rates of herbivory within ecological communities. In a series of simulated herbivory experiments, I quantified how the timing of leaf damage in mountain sagebrush (Artemisia tridentata ssp. vaseyana) affects future herbivory. An identical leaf damage treatment was applied across 12 time windows to test how the effectiveness of response to herbivore damage changes along three interacting temporal scales: diel, seasonal, and annual. In contrast to several studies demonstrating induced resistance to herbivory in sagebrush, prevention of future herbivory was only detected following summer afternoon leaf damage in one of three years. These findings suggest that the timing of experimental leaf damage is one of many factors contributing to variability in field-based plant defensive induction studies.