by Carl Strang
April was a cooler, more seasonable month than March, which had remarkably early flowering dates for the early plants (recap: March had medians of 32 days earlier than in 2009, 21 days earlier than 2010, and 31.5 days earlier than last year). Since flowering is related to cumulative soil warming, I expected April to show a continuation of the early season, though not necessarily as dramatic. Such was indeed the case.
The plants that bloomed in April this year at Mayslake Forest Preserve were a median 24 days earlier than in 2009 (25 species, range 14 to 55 days earlier), 13 days earlier than in 2010 (25 species, range 3 to 47 days earlier), and 27 days earlier than last year (31 species, range 12 to 37 days earlier).
I don’t find every plant every year, but the sample size is large enough to be representative.
So, plants continue to bloom 2-4 weeks early this year. The difference should decline each month, as soil heat approaches its effective maximum while later-season plants come into play.