Climate drives variability in pollen emission and tree growth: Linking aerobiology and dendrochronology in urban forests

Climate variability influences reproductive effort and radial growth leading to apparent trade-offs in trees. However, these relationships have not been investigated considering two major carbon sinks, namely pollen and wood production. This research gap is particularly important in urban forests subjected to rapid warming and increasing pollen-related health risks. We quantified and related climate variables, airborne pollen production (1993–2024) and tree-ring data in Ourense, northwestern Spain, at the transition between Mediterranean and temperate climates. Four tree species were studied, two were sampled in lowland riparian forests ( Alnus glutinosa , Fraxinus angustifolia ) and other two in upland montane forests ( Quercus robur , Pinus pinaster ). The cumulative pollen concentration during the main pollen season (Seasonal Pollen Integral, SPIn) showed the importance of antecedent climate during reproductive development. A positive relationship of SPIn with previous-year October maximum temperature was detected in all species. Radial growth of riparian species responded positively to winter–spring moisture and temperature, whereas growth of upland species was enhanced by warmer spring conditions. Negative relationships between pollen production and tree growth were detected only in Quercus , The current-year pollen–growth association was driven by climatic variability, whereas the negative association between current-year SPIn and previous-year growth remained significant after accounting for climatic conditions. These patterns suggest that carry-over effects may contribute to the coupling between prior growth and subsequent pollen emission. Pollen emission and growth respond to distinct climatic drivers depending on phenological timing, with carry-over effects contributing to pollen production during the subsequent flowering season.