Kim, J., Kim, K. R., Han, M. J., Cho, Y., & Jeong, S.* (2025). Decreasing annual pollen loads in evergreen needleleaf species (Pinaceae) by the earlier end of the spring pollen season. Agricultural and Forest Meteorology, 373, 110753. https://doi.org/10.1016/j.agrformet.2025.110753

Abstract:

Globally, the annual pollen integral (APIn) of allergenic plant species has increased owing to climate-induced ecosystem changes; however, the role of phenology in APIn changes remains underexplored. This study examined the direct and indirect effects of climate variables and pollen phenology on APIn in Korean Pinus spp. using 23 years of ground-based data from seven stations. Phenological stages—start (SPS), end (EPS), and length (LPS) of the pollen season—were estimated using two different methods: percentage-based and threshold-based. At the same time, various meteorological indicators related to temperature and precipitation were calculated from daily observation data. Despite interannual warming, APIn significantly declined at most stations by about 2 % per year, independent of temperature trends. Path analysis revealed that temperature sequentially influenced pollen phenology: higher seasonal temperatures advanced SPS (β = –1.19, p < 0.01) and EPS (β = –0.73, p < 0.05), leading to significant indirect reductions in APIn. Bootstrapped mediation models confirmed adverse indirect effects through EPS (β = –204.21) and multi-step paths involving SPS and LPS.
In contrast, early-season rainfall showed limited influence, with a single significant path through EPS (β = 110.90). These findings reveal that phenological advancement can suppress pollen production under favorable climatic conditions. Climate-pollen interactions in coniferous forests are thus better understood through a phenological mediation framework, which captures the cascading effects of shifting seasonal timing. Monitoring phenological change offers a critical tool for predicting ecosystem-level responses to climate change and informing forest management in temperate regions.