Bridging aerobiological and floristic assessments: evaluating allergenic mismatches in an urban green space

Urban green spaces are vital components of green infrastructure, providing a wide range of ecosystem services; however, they may also generate disservices such as increased airborne pollen allergenicity. Climate change is amplifying these effects by lengthening pollen seasons, making it essential to assess the allergenic potential of urban vegetation for informed urban planning and public health. This study evaluated the floristic composition and allergenic potential of a major urban garden in Tetouan, Morocco. A comprehensive floristic inventory was conducted to identify plant species, count individual plants, and determine surface coverage, while species diversity was assessed using the Shannon index. The potential allergenicity value (PAV) was applied to calculate the index of urban green zone allergenicity (I_UGZA). In total, 75 plant species from 36 families, comprising 1285 individual plants, were recorded, covering approximately 44% of the garden's surface. The garden exhibited high botanical diversity (H' = 3.73), yet the allergenic risk was low (I_UGZA = 0.048), primarily due to regular maintenance, a dominance of entomophilous species, and minimal presence of highly allergenic taxa such as Cupressus sempervirens and Casuarina equisetifolia, which together covered less than 1% of the area. While citywide airborne pollen monitoring indicates substantial pollen diversity and load, the localized allergenic potential within the garden remains limited. Therefore, site-specific assessments are critical to complement broader aerobiological data, and enhancing plant diversity while avoiding invasive allergenic species, along with sound maintenance practices, can help mitigate allergy-related impacts and improve the resilience of urban green spaces in the context of climate change.