An aeropalynological study of metropolitan Toronto |
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Authors: | Christine A Rogers |
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Institution: | (1) Life Science, Scarborough College, University of Toronto, 1265 Military Trail, M1C 1A4 Scarborough, Ontario, Canada;(2) Present address: Biological Science, University of Tulsa, 600 S. College Ave., 74104 Tulsa, OK, USA |
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Abstract: | This study uses 6 years of atmospheric pollen data to examine temporal variability of airborne pollen concentrations at various
scales. Airborne pollen was collected from 1985 to 1990 with a Burkard trap, located 18 m above ground at Scarborough College,
Toronto, Canada. Pollen season parameters are defined and summarized for all taxa in preparation for developing forecasting
models. Annual totals of pollen concentration show great interannual variability. The highest coefficient of variation occurs
inTsuga, Fraxinus, Betula andFagus, while the lowest inQuercus andAmbrosia. Some taxa show periodic cycles consistent with mast reproductive behaviour. In many studies, the start of the pollen season
is defined as an arbitrary percentage of the annual sum. As a result, the start of the season cannot be identified until the
season has passed. As well, due to large fluctuations in annual sum, start dates are more variable. This is not practical
for the purposes of forecasting. In this study, the start of the pollen season is defined by a critical concentration threshold
which signals the onset of the main pollen season in all years. These critical levels ranged from 2 to 60 grains/m3 for the abundant taxa. Interannual variation in the start of the season is approximately 20 days for tree taxa, 5 days for
Poaceae, and 2 days forAmbrosia. For many plants, dehiscence is triggered at a critical level of accumulated degree-days. Since annual rates of temperature
increase show great variation, there is also interannual variability in the onset of pollen release. Multi-year average pollen
curves incorporate these differences in onset and may give an inaccurate representation of the pollen season in a typical
year. This paper presents a method of aligning yearly pollen curves to reduce seasonal variation and more accurately represent
both the average timing and magnitude of the pollen season. For some types, such asBetula and Poaceae, the resulting curves are positively skewed. Tree taxa, in general, exhibit a more symmetric pollen concentration
curve. Aligned average pollen concentration curves are presented for Toronto in the form of a pollen calendar. In addition,
phenological data for all common taxa are summarized. |
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Keywords: | Phenology Start date Pollen calendar Alignment Aerobiology |
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