Each year seems to offer variation in Spring flowering times. Over a long period of time, however, phenology of blooming plants provides a strikingly different result–uniformity.
This conclusion was corroborated by a 30 year Minnesota study.1 Phenology is “the study of the relationship between climate and periodic biological phenomena.” In the Minnesota case, the specific definition was “…leaf bud development and the flowering of a select group of trees and shrubs located on or in the vicinity of the University of Minnesota St. Paul campus.” It’s of special significance that the data were recorded by the same observer throughout the 30 years.
The results showed great differences between years. But when looked at in 10-year increments, little variation was seen. According to the study, “The small and inconsistent shift in average dates from decade to decade provides evidence…that these events have not been occurring consistently earlier or later in recent years.” Another set of data compiled over a sixty three year period showed the average date for “Pink Bud Stage” was May 7, almost exactly the same as the four-decade average date, May 7 and 8. The same was true for “Apple Petal Fall.” Both sets of figures show May 22 or 23.
These data are more than just passing interest. They have been used by entomologists to schedule field work, to apply pesticide, and to educate students. And beekeepers can also average their observations over many years, learning to predict when critical management techniques might be necessary.
Although photoperiod is important in temperate areas, in the subtropics and tropics, moisture availability becomes more critical than hours of daylight which don’t vary significantly throughout the year. Thus, the apicultural calendar differs in subtropical Florida from that found in the temperate mid west, as does a typical one from tropical Latin America.
An important conclusion drawn from the Minnesota study described above is the value of extended observation. Without information like this it would be impossible to develop an apicultural calendar. The same is true for other aspects of the beekeeping operation.
Unfortunately, accelerated climate change appears to reveal that the conventional wisdom of the apicultural calendar as being invariate can no longer be relied on. It is at risk of being overturned because the average bloom time is no longer the same, but appears to be moving much more radically than in the past. The could spells bad news for many plants and the animals that depend of them. See the honey bee net project for more insight into this phenomenon.
1 “Minnesota Springs–A Thirty-Year Record,” Minnesota Horticulturist, March, 1971.