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Harvard Forest Symposium Abstract 2008

  • Title: Woody Species Phenology, Prospect Hill Tract, Harvard Forest - 2007
  • Primary Author: John O'Keefe (Harvard Forest)
  • Abstract:

    2007 was the eighteenth 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 nine, 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. In 2002 the number of species observed in the fall was reduced to fourteen, including including red maple (Acer rubrum), sugar maple (A. saccharum), striped maple (A. pensylvanicum), shadbush (Amelanchier laevis), yellow birch (Betula alleghaniensis), black birch (B. lenta), paper birch (B. papyrifera), beech (Fagus grandifolia), white ash (Fraxinus americana), black gum (Nyssa sylvatica), black cherry (Prunus serotina), white oak (Quercus alba), (Q. rubra) and black oak (Q. velutina).

    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 2006-2007 proved variable. December and much of January were very mild and drier than normal. Late January and February were cold and snowy. Spring started cold and snowy in March and cold and very wet in April, but turned cloudy and then turned warm and drier than normal in May and June. Summer was generally mild and drier than normal, especially in August. September and October stayed mild and quite dry. The first frost at Harvard Forest didn’t occur until October 28th, the latest first frost observed since 1990 and more than three weeks later than the mean first frost date observed 1990-2006. The prior latest first frost date was October 25th in 2005.

    For most species initial bud break in 2007 was slightly later than the mean (Table 1/Figure 1), putting 2007 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 extremely late first frost, fall coloration and leaf fall in 2007 were only slightly later than the mean, perhaps influenced by the very dry late summer and fall, again pointing out how poorly the factors controlling leaf senescence are understood.

    The extreme lateness observed in 2002 and 2005 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 slightly 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 our poor understanding of the factors controlling them, and to emphasize the need for long-term data sets.

  • Research Category: Forest-Atmosphere Exchange

  • Figures:
  • phengraph 2007.pdf
    JOK phenology table 2007 font8.pdf