Nature journal is filled with peak dates for season of transition
Its the time of the illuminated woods, but beautiful fall foliage colors are seen along city boulevards, in yards and gardens, and even on the sides of some buildings where Boston ivy or Virginia creeper vines display handsome red leaves.
Millions of people travel countless miles on autumn weekends to see New Englands concentrated palate of fall foliage. Thats great, but people in Minnesota and Wisconsin, China and Japan, Iceland, Germany and other locations in the Northern Hemisphere can also enjoy the foliage color season that often runs from September to November.
There is a date for each area when it hits peak. That special date is when the foliage colors are spectacular, considering the many trees, shrubs ad vines that give us the show. Oct. 7 was the average color overall peak date from 1969 to 2013 in the Waconia (where I live) and the metro area. My field notebook shows Oct. 14 last year as the overall peak of fall colors for the Twin Cities and larger area.
The striking color changes that take place, as deciduous woody plants prepare to drop their leaves, are triggered by shortening days and cooler weather. Then the food-making process and the making of chlorophyll ceases. As the green colors fades, two underlying pigments called carotene and xanthophyll are unmasked, leaving yellow.
Red coloration appears only in those leaves that have certain sugars or tannins that combine with other substances to produce the red pigment (anthocyanin) that gives the woody plants their glorious crimson.
Jim Gilbert taught and worked as a naturalist for 50 years.