AIRSPORA OF JOHANNESBURG AND PRETORIA, SOUTH-AFRICA, 1987/88 .1. POLLEN CALENDARS

Two Burkard seven-day recording traps have been in operation in the cities of Johannesburg and Pretoria since 1987. Pollen calendars average data for 1987 and 1988. Grass pollen is the most significant contributor in absolute and relative terms. This taxon comprises 52% of total regional pollen for the study period. Pollen of alien northern hemisphere trees is abundant, relative to that of native trees. This is attributed partly to the paucity of trees in the natural vegetation, and partly to their entomophilous nature. The flowering season for exotics is very short, possibly due to the short spring season. The greatest proportion of pollen, 58,8%, is nonseasonal. Species in this category flower throughout the year. 28.4% of taxa are spring-flowering. Annual variability is marked for most taxa.