Pasture Foliage Changes over the Years, Harvard Forest
The photographs in the following presentation document the changes in forest trees at the margin of the pasture, adjacent to the headquarters of the Harvard Forest. These photographs were taken starting Autumn, 2005 by John O'Keefe, and show the timing of both autumn leaf colors and leaf fall and the the leaf out in individual trees in a typical year.
In, 2006, despite the very mild and dry winter, leaf out (leaves emerged from 50% of the buds) occurred at the end of the first week in May, about two days later than the average date for the previous 16 years. This date is determined by averaging the date of leaf out of six species, including: red maple, red oak, yellow birch, white oak, striped maple and witch hazel. Due to cool, wet weather in the middle of May, leaf expansion proceeded rather slowly until the last week of May which was very warm. Learn more about this study of woody species leaf phenology.
Despite a relatively mild fall and no frosts until the first week of October, leaf drop in 2006 was the earliest yet observed by a day: compare the Oct 17, 2005 picture with the October 15, 2006 one. There are obviously many factors involved in fall phenology that are not yet well understood.
| October 17, 2005 | October 15, 2006 |
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