Herbarium Specimens Predict Flowering Times of Grasses that Contribute to Pollen Allergies

 By Richard B. Primack

 

“The old naturalists were so sensitive and sympathetic to nature that they could be surprised by the ordinary events of life.” Henry David Thoreau in his Journal.

 

The grass family is responsible for many pollen allergies, which are predicted to increase with global climate change. Unfortunately, since standard airborne pollen monitoring techniques don’t provide species-specific pollen identification, these methods end up grouping all grass species together which undermines their usefulness.

Figure 1.  Locations of airborne pollen monitoring stations in Denmark.

 

As reported in a recent article, we obtained flowering data for 12 allergenic grass species using thousands of herbarium specimens collected across Denmark over 190 years. We then compared these data to pollen monitoring data. 

Figure 2.  Herbarium specimen of velvet grass (Holcus lanatus) collected in Denmark on July 1, 1870.

Seven of the grass species included in the data are major contributors to airborne pollen based on their relative abundance in the wild and the overlap of their flowering times, determined based on herbarium collections, with when maximum airborne pollen loads are detected. In addition, many grass species are also flowering earlier in response to warmer spring temperatures.

Figure 3. Velvet grass herbarium specimens with flowers have the same seasonal distribution as the pollen density at airborne monitoring stations. (DOY=Day of Year) 

Figure 4.  Creeping velvet grass (Holcus mollis) herbarium specimens with flowers do not have the same distribution as the pollen density at airborne monitoring stations. (DOY=Day of Year)  

This type of data derived from natural history collections can contribute to the advancement of pollen forecasting for asthma and allergy patients both under current conditions and in the coming decades as climate change continues.

 

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