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Harvard Forest Symposium Abstract 2020

  • Title: Woody Species Phenology, Prospect Hill Tract, Harvard Forest - 2019
  • Primary Author: John O'Keefe (Harvard Forest)
  • Abstract:

    Woody Species Phenology, Prospect Hill Tract, Harvard Forest - 2019

    J. O'Keefe

    2019 was the thirtieth year in our ongoing investigation of the timing of woody vegetation development (phenology) during the growing season (Data are available at - 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) inter-annual variation in the timing of spring development, but good relative rank-order 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 through full development 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). An additional seven species, including shadbush (Amelanchier sp.), black birch (B. lenta), paper birch (B. papyrifera), alternate-leaved dogwood (Cornus alternifolia), hawthorn (Crataegus sp.), black cherry (Prunus serotina), and black oak (Q. velutina), continue to be observed through bud break. This subset of important, representative species has allowed 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. Approximately 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 red maple (Acer rubrum), sugar maple (A. saccharum), striped maple (A. pensylvanicum), shadbush (Amelanchier sp.), 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), red oak,(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 2018-19 featured a warm, wet December followed by a near normal, but wet January and then a near normal February. Spring began cool and dry in March, turned warm and very wet in April, and then turned cooler and drier in May. June was near normal in both temperature and precipitation, July was very warm and a bit wet, and August was mild with near normal precipitation. September was mild and rather wet, October was warm and wet, and November turned cold and dry. The first frost at Harvard Forest occurred on October 5th, close to the mean first frost date observed from 1990-2018, but that was the only frost in October.
    Bud break in 2019 averaged several days later than the long-term mean (Figure 1(Table 1)/Figures 2&3). However, red oak, the dominant tree species at Harvard Forest, maintained a trend toward earlier leaf emergence. Leaf development then progressed a bit slowly, but steadily, with 75% leaf development occurring almost a week later than the 29-year mean. Despite the mild early fall, 50% leaf fall in 2019 was close to the long-term mean (Figure 4). 2019’s somewhat late leaf emergence date coupled with near normal leaf senescence resulted in a somewhat shorter growing season than the long-term mean (Figure 5).
    The very earliness of leaf emergence in 1993, 1998, 2010 and 2012, and lateness in 1992, 1997, 2003, 2014 and 2016, along with the extreme earliness of leaf senescence and fall in 1994, 1995, 2006 and 2013 and lateness in 2002, 2015, 2016 and 2017, continue to point out the extreme variability in the timing of these events and the complexity of the factors controlling them. These observations emphasize the need to continue these long-term studies and data sets.

  • Research Category: Forest-Atmosphere Exchange

  • Figures:
  • Phenology_JOK_Figure 1_Table 1-2019-abstract.pdf
    JOK phenology abs-2019 Figure 2.pdf
    JOK Phenology abs-2019 Figure 3.pdf
    JOK Phenology abs-2019 Figure 4.pdf
    JOK Phenolgy abs-2019 Figure 5.pdf