Do Botanical Gardens Pose a Pollen Allergenicity Risk? A Multi-Method Assessment Integrating Species-Specific Values of Potential Allergenicity and Pollen Concentration Monitoring

Botanical gardens serve dual functions of species conservation and public education. In these open-air recreational environments, the pollen allergy risk associated with the garden’s structure may impose considerable impacts on public health, yet this risk is often overlooked in landscape design. In this study, we conducted a comprehensive assessment of pollen allergy risk posed by landscape trees in the Chengdu Botanical Garden through landscape tree species composition surveys, flowering phenology observations, potential allergenicity values (VPA) estimation, and year-round pollen concentration monitoring. Six functional zones with decreasing disturbance intensity were designated in the garden. A total of 114 species (42 families, 84 genera) and 1582 individual trees were recorded, of which 76.32% are native to China. The diversity of the garden is moderately high (richness 44.8, Shannon–Wiener 3.13, evenness 0.82). A low VPA profile was observed in the garden. Low-VPA species accounted for 71.93% of species and 75.60% of individuals, while medium-VPA species represented 21.93% of species and 18.65% of individuals. High-VPA species comprised only 6.14% of species and 5.75% of individuals. Despite this low-VPA composition, pollen concentration remained unexpectedly high. Pollen monitoring showed that mean spring pollen concentrations in March and April reached 207.47 and 243.56 grains/cm2, respectively, corresponding to an extremely high risk level (Level 5). Moreover, an early peak appeared in late February (104.90 grains/cm2, Level 3). These elevated concentrations were primarily attributed to a highly concentrated flowering phenology, with 91.22% of landscape tree species flowering from February to May, among which 50.87% bloomed in March and April. Furthermore, sunshine duration exhibited the strongest negative association with spring pollen concentration, while mean wind speed exerted an independent positive effect after controlling for confounders, indicating that meteorological conditions significantly modulate actual exposure risk. These findings indicate that pollen allergy risk assessment should integrate both pollen concentration monitoring and tree VPA classification. Based on a risk framework coupling these two dimensions, the ecological conservation area (habitat protection, no public access) was identified as a high-risk core zone, the themed specialized garden area (specialist taxa display) and ecological recreation area (nature recreation, limited public access) as concentration-dominated secondary risk zones, and the educational leisure area (exhibitions and leisure), as a year-round safe zone. Given its dual mission, management should balance conservation and health through visitor guidance, physical barriers, and phenological regulation, rather than by removing allergenic species.