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Harvard Forest Symposium Abstract 2007

  • Title: Woody Species Phenology, Prospect Hill Tract, Harvard Forest - 2006
  • Primary Author: John O'Keefe (Harvard Forest)
  • Abstract:

    2006 was the seventeenth year in our ongoing investigation of the timing of woody vegetation development during the growing season. However in 2002 the scope of the study was changed significantly. For the first twelve years we observed bud break, leaf development, flowering, and fruit development on three or more individuals of 33 woody species at 3-7 day intervals from April through June. These observations documented substantial (up to three weeks difference) interannual variation in the timing of spring development, but good relative consistency among species and among individuals within species during these twelve years.

    Therefore, starting in 2002 we maintained the same observation schedule, but reduced the number of species observed to eight, including red maple (Acer rubrum), sugar maple (A. saccharum), striped maple (A. pensylvanicum), yellow birch (Betula alleghaniensis), beech (Fagus grandifolia), white ash (Fraxinus americana), witch hazel (Hamamelis virginiana), red oak (Quercus rubra), and white oak (Q. alba). This subset of important, representative species should allow us to continue to characterize leaf development each spring, and document inter-annual variability while reducing the resources required for the study significantly.

    We have also recorded fall phenology since 1991, with the exception of 1992. Weekly observations of leaf coloration and leaf fall begin in September and continue through leaf fall. All individuals are located within 1.5 km of the Harvard Forest headquarters at elevations between 335 and 365 m, in habitats ranging from closed forest, through forest-swamp margins, to dry, open fields.

    The winter of 2005-2006 was quite variable. December was cool and wet. January was very mild and February was cold and snowy. Spring started mild and dry in March and April, but turned cloudy and wet in May and June. Summer was generally mild and somewhat drier than normal. September was mild and dry and October stayed mild but turned wet. The first frost at Harvard Forest didn’t occur until October 13th, twelve days earlier than the latest first frost date (October 25th) in 2005, but still eleven days earlier than the mean first frost date since 1990.

    For most species initial bud break in 2006 was slightly later than the mean (Table 1/Figure 1), putting 2006 in the group of neither early nor late years. Leaf development then proceeded normally during May with 75% leaf development also occurring slightly later than the mean. Despite the generally mild fall and late first frost, fall coloration and leaf fall in 2006 were among the earliest yet observed. This earliness, not directly related to severe drought or early cold, points out how poorly the factors controlling leaf senescence are understood.

    The extreme lateness observed in 2002 and 2005 has expanded the variability observed in leaf senescence significantly, so that it more closely resembles the variability observed in leaf emergence over the course of this study, and called into question our previous assumption of much less variability in the timing of fall events. In fact, despite the earliness in 2006, fall appears to be occurring later over the course of this study while spring shows great variability but no trend. These observations continue to point out the variation in the timing of these events and emphasize the need for long-term data sets.

  • Research Category:

  • Figures:
  • symp07abs-jok-phen table.pdf
    symp2007-color graph 1990-2006.pdf