Bees are critical to the survival of myriad ecosystems around the world, and their pollination is worth billions of dollars every year in the U.S. and abroad. Their populations have been declining for decades due to climate change and habitat loss, posing a threat to global food security.
Agricultural yields can be threatened by a simple decrease in bee populations, as well as by changes to the crops' growing seasons and the bees' flight and pollination seasons. If the crops are ready to be pollinated but the bees aren't around to do the job — no luck.
While changes to bee species' abundances and diversity have been well-studied, biologists don't yet know how in sync bees are with crops from region to region, or how that's changed over time. A new study in Global Change Biology examined how wild bee populations in Belgium have shifted when and how long they're active — their "flight period" — over the past 70 years.
The study found that 61 percent of Belgium's wild bees declined over that time span, but not all bee species had the same response to climate and land-use changes. There are "winners" and "losers": southern bees adapt more readily to warmer temperatures, and bees with bigger ranges can cope better with land-use change. That makes generalizing predictions about future changes tricky.
Additionally, two of the bees' behaviors, flight period and occupancy (range), varied by species. Those behaviors are affected by temperature changes and agricultural expansion, both of which increased over 70 years. As a result, the bees' pollination season was 9-15 days shorter and started a few days earlier.
With an estimated 11 percent of crops in Belgium depending on pollination for success, that's a significant shift. The timing of crops' growing season and bees' pollination is a delicate balance. While wild bees' pollinating can be supplemented with domestic hives, it can be less efficient than wild pollination and, because wild bees are free, it's always more expensive.
Bees' critical role in agriculture isn't new, but scientists are just beginning to understand their complex responses to climate change and agriculture, and what that means for pollination seasons. Until more research is done, changes to pollination seasons will remain up in the air.