You are here

Harvard Forest >

Harvard Forest Symposium Abstract 2017

  • Title: Woody Species Phenology, Prospect Hill Tract, Harvard Forest - 2016
  • Primary Author: John O'Keefe (Harvard Forest)
  • Abstract:

    Woody Species Phenology, Prospect Hill Tract, Harvard Forest - 2016

    J. O'Keefe

    2016 was the twenty-seventh 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 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 2015-16 featured record warmth with very little snowfall. Spring began warm, but turned cool and cloudy in April with below normal precipitation. May was dry with near normal temperatures. June, July and August were warm and much drier than normal. The fall remained quite warm and September was dry, October rather wet and November drier than normal again. The first frost at Harvard Forest occurred on October 25th, more than three weeks later than the mean first frost date observed from 1990-2015, continuing the pattern of much later first frost dates over the past decade.
    Despite the record mild winter, bud break in 2016 was much later than the long-term mean thanks to the cool April (Figure 1(Table 1)/Figures 2&3). This very late leaf emergence despite a very warm winter through March points out the importance of the weather in April in determining the timing of leaf emergence. This late leaf emergence also served to compress the leaf emergence period, with some typically early species leafing out in early May within about a week of typically late species. Leaf development then progressed steadily, with 75% leaf development occurring just slightly later than the 26-year mean. The mild fall and very late first frost date led to 50% leaf fall in 2016 being the latest so far observed (Figure 4). 2016’s very late leaf emergence coupled with the latest leaf senescence resulted in a slightly longer growing season than the long-term mean, maintaining the trend toward a somewhat lengthened growing season over the period of our observations (Figure 5).
    The very earliness of leaf emergence in 2010 and 2012, and lateness in 2014 and 2016, along with the extreme lateness of leaf senescence and fall in 2002, 2015 and 2016, 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_Table 1-2017-abstract.doc
    Phenology_JOK_Figure 2-2016.pdf
    Phenology_JOK_Figure 3-2016.pdf
    Phenology_JOK_Figure 4-2016.pdf
    Phenology_JOK_Figure 5-2016.pdf