How much pollen is out there floating around, anyway?

As a botanist, North Carolina resident and seasonal allergy sufferer, I experience a triple whammy of acute awareness when spring begins. This week marks the start of a curious natural phenomenon: the time of year when one puzzles over the greenish-yellow waft of particles covering everything, necessitating the use of windshield wipers to allow driving despite the onslaught of plant reproductive material (see right).

Indeed, North Carolina flora are spreading their gametes with a vengeance this time of year. Never before have I experienced such a visual demonstration of the prolific nature of pollen before, so I took the opportunity to perform a few "back of the envelope" calculations. How much pollen is actually being produced, anyway? I was pleased that forestry researchers have actually done enough of the hard work collecting empirical data about this topic to make discussion possible.

Loblolly pine (Pinus taeda) is the predominant species in most areas of the southeast and are widely planted for commercial timber. An adult tree (16 m) produces 81 grams of pollen a day for 2-4 weeks. Let's assume that means ~1 kg of pollen per tree per season (my sinuses are already saying "CRAP"). An estimated 3.3 million acres in North Carolina alone are planted stands of loblolly pine (although it's dominant on an estimated 29 million acres). I will assume density of planted stands is only 100 trees per acre. This is dramatically lowballing the number of trees, but this is allowing for a few considerations: 1) trees don't start producing pollen until they are 10-15 years old, and 2) stands of trees are sometimes planted at high density and later thinned to remove diseased/damaged/crowded trees.

So 3.3 million acres of trees, with 100 trees per acre, that's over 300 million trees. That means loblolly pines in North Carolina are producing 300 million kilograms of pollen each year. That's a level of scale my brain is having a tough time processing. The population of North Carolina is a little less than 10 million people. That means we each get 30 kg of loblolly pine pollen a year! Think of a large adult German shepherd. That's how much pollen. Per person.

But wait! It gets better! Because loblolly pines also occur in natural populations, and they're not the only plants producing pollen. They're not even the only pine trees producing pollen. And guess what? Pollen can travel over 41 kilometers in the air. And each gram of pollen contains over a million grains. I'm still having a tough time comprehending this level of scale, and am half hoping someone will say I've grossly miscalculated by an order of magnitude (the other scientist half of me, of course, wants to be right). Well, now that I've thoroughly discouraged myself, I think I'll get back to work.

Literature referenced:
Baker, James B. and O. Gordon Langdon. Loblolly pine. Silvics of North America. Agriculture Handbook 654. USDA Forest Service.

Biofuels Center of North Carolina. 2011. Loblolly Pine Trees. Biofuels Wiki.

Williams, Claire G. 2009. Conifer Reproductive Biology. Springer: New York. 169 pages.

Williams, Claire G. 2010. Long-distance pollen still germinates after mess-scale dispersal. American Journal of Botany 97(5): 846-855. doi: 10.3732/ajb.0900255 (research supported by NESCent!)