The potential effects of tree planting on allergenic pollen production in New York City

Tree selection decisions affect urban pollen production but the overall importance of tree planting to airborne pollen concentrations remains poorly understood. A synthesis of existing data and available literature could inform tree -planting decisions and potentially help reduce future airborne pollen concentrations. This is especially relevant for the many cities that are considering tree planting campaigns, such as New York City. Here, I examine which allergenically -important tree taxa could be most influenced by municipal tree selectio n decisions in New York City by comparing tree species abundance from a representative plot-based city-wide tree survey with a street tree inventory. I then estimate pollen production from several allergenic tree taxa by combining these tree datasets with allometric equations of pollen production as a function of tree size. Pollen production is also compared to several years of airborne pollen measurements. The potential effect of a proposed planting campaign is estimated over time by combining growth rate equations with pollen production equations. Several tree genera are especially important producers of allergenic pollen in New York City, including Quercus, Platanus, Morus , and Betula ; these taxa also comprise 71% of airborne pollen measured and 93% of estimated pollen production (107 quadrillion pollen grains ; however pollen production could not be estimated for all taxa). Platanus × acerifolia is predominantly a street tree, indicating that previous municipal planting decisions have resulted in its current abundance (it accounts for 34% of total street tree basal area and has an estimated annual pollen production of almost 30 quadrillion grains) and will determine its future abundance. In contrast, Morus and Betula are uncommon as street trees, indicating that municipal tree planting campaigns are unlikely to substantially affect their pollen production rates in NYC. Quercus was the largest estimated producer of pollen in NYC (62 quadrillion pollen grains) and accounted for almost 25% of airborne pollen co llected, but its very high abundance outside of street trees suggest that the relative effect of planting trees in this genus will be relatively small. Overall, this study demonstrates how tree planting decisions can have important and long-lasting consequences for allergenic pollen production in certain circumstances, suggesting that pollen allergenicity should be considered in future tree selection decisions. ### Competing Interest Statement This study was funded by Bayer Health