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Harvard Forest Symposium Abstract 2009

  • Title: Woody Species Phenology, Prospect Hill Tract, Harvard Forest - 2008
  • Primary Author: John O'Keefe (Harvard Forest)
  • Abstract:

    2008 was the nineteenth 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 2007-2008 proved somewhat variable. December was rather cold, but in January it turned much warmer than normal and remained mild through April. January was rather dry, but February through April were much wetter than normal. May was cool and drier than normal. Summer was generally mild and quite wet, especially July. September and October stayed mild and September was very wet. The first frost at Harvard Forest didnít occur until October 8th, nearly two weeks later than the mean first frost date observed 1990-2007. This continues the pattern of quite late first frosts in the past several years.



    For most species initial bud break in 2008 was slightly earlier than the mean (Table 1/Figure 1), putting 2008 in the group of neither very early nor very late years. However, red oak did have the second earliest bud break observed to date. Leaf development then proceeded a bit slowly during May with 75% leaf development also occurring slightly later than the mean. The generally mild fall and rather late first frost, led to fall coloration and leaf fall in 2008 that were later than the mean and the fifth latest observed over 17 years of observation.



    The extreme lateness in leaf fall 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 early senescence in 2006, fall appears to be occurring slightly later over the course of this study while spring shows great variability but no real trend, resulting in a slightly lengthened growing season. 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:
  • JO'K's Phenology Font 8-1990-2008.pdf
    Fig 1-phengraph 2008.jpg