Ecological and allergenic significance of atmospheric pollen spectra from a Grassland-Savanna ecotone in North West province, South Africa

Southern Africa’s floral, topographic and climatic diversity manifests in distinctive bioregions where aerobiology studies are needed to manage allergenic health problems, especially in urban areas. Previous studies underline different seasonal pollen fluctuations for the biomes, encouraging regional studies. These studies have been previously restricted to large cities such as Cape Town, Johannesburg and Pretoria whereas small cities such as Potchefstroom in the North-West province are understudied. The South African Pollen Monitoring Network (SAPNET) seeks to fill this lacuna, enhancing ecological and health-related knowledge, with regard to the allergenicity of the recorded pollen. Here, we investigate plant phenology and resulting pollen production within the Grassland and Savanna biomes around Potchefstroom, a fast-growing city in the North West province, comparing it with other SAPNET sites. As a SAPNET initiative, pollen monitoring in Potchefstroom involved monthly collections using a Lanzoni 7-day spore trap over 13 months from December 2022 to 2023. This facilitated the development of a preliminary pollen calendar and a pollen atlas, detailing pollen types’ morphology, ecology, pollination modes, and allergenicity. Initial findings revealed Potchefstroom’s pollen calendar, with tree pollen (60% of the Annual Pollen Index (API)) mainly from northern hemisphere species such as Cupressus (c. 11% of API) and Platanus (c. 18%), which released pollen in spring. Grass pollen was predominant from November to April (c. 18% of API). Potchefstroom recorded South Africa’s highest levels of Ambrosia pollen (c. 7% of API), a major allergen, in March and April. Noteworthy is the unusual abundance of pollen of the neophyte Ulmus (c. 14%) in December. This study highlights the pollen patterns of the Grassland and Savanna biomes around Potchefstroom. The region, with its mosaic of urban spaces, natural grass-/woodland, and agricultural land, exhibits distinct characteristics when contrasted with major, more densely populated cities such as Bloemfontein, Pretoria, and Johannesburg.