May Phenology 1: First Flowering Dates

by Carl Strang

The end of May brings the next opportunity to compare seasonal timings between 2013 and the previous years. There’s nothing special in this choice, except that months are a familiar common language and they provide a sensible number of comparisons each year. The data I collect are limited to Mayslake Forest Preserve, because I am out in that property most regularly and so can make the most consistent comparisons. Today I’ll share the first flower dates, which provide the soundest results.

As expected, flowering phenology this May was much later than last year, a median 24 days later for 73 species. This is 10 days less than the April difference, but it is typical for the first flower dates to converge as the season progresses.

The broad-leaved woolly sedge, Carex pellita, was the median species this time.

The broad-leaved woolly sedge, Carex pellita, was the median species this time.

If we jump to the other early year, 2010, the difference also is less. The median first flower date was 12 day later in 2013 than in 2010 (54 species). The corresponding difference in April was 17 days.

Yellow sweet clover fell on the 12-day median difference.

Yellow sweet clover fell on the 12-day median difference.

The surprise came from the comparison between 2013 and the other late years, 2011 and 2009. The median difference was exactly 0 days for 2011 (67 species), and 2013 was only one day later than 2009 (53 species; the respective differences were 4.5 and 5 days in April).

Common spiderwort first bloomed one day later in 2013 than it did in 2009.

Common spiderwort first bloomed one day later in 2013 than it did in 2009.

All of this continues to underline how unusual last year was.

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