LAUSR

Plant reproduction has broad implications for ecology and society (e.g., production of allergenic pollen), and a number of processes that affect flowering are affected by climate. In this study, we tested for variation in traits related to pollen production by the allergenic plant, common ragweed, across a climate gradient in Massachusetts. We tested whether traits that are easily-measured in the field could be used to predict differences in spike length, a known proxy for allergenic pollen production, and the timing and duration of flowering. We also tested whether flowering time and allometric estimates of spike length varied across the climate gradient, to better understand climate effects on future pollen production. We found that height predicts inflorescence length, but the slope of the relationship between the two traits is steeper in cooler climates, suggesting ragweed growing in cool climates produces more pollen per unit of vegetative height than ragweed in warm climates. Cool climates were also associated with larger and higher numbers of flowers and earlier and longer periods of flowering. Thus, we provide improved estimates of local pollen exposure by establishing variation in timing and output of flowering across a regional climate gradient, and at a spatial scale that may be useful for developing management strategies for allergenic plants.