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Harvard Forest Symposium Abstract 2006
- Title: Woody Species Phenology, Prospect Hill Tract, Harvard Forest - 2005
- Primary Author: John O'Keefe (Harvard Forest)
- Additional Authors: John O'Keefe (Harvard Forest)
- Abstract:
2005 was the sixteenth 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), 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 2004-2005 was colder than normal with a cold and snowy March. April was milder but May turned very cold and cloudy. By summer the pattern was milder and dry. September was wet and mild. The first frost at Harvard Forest didn’t occur until October 25th, ten days later than the prior, latest first frost date in 2002, and 25 days later than the mean first frost date since 1990.
For most species initial bud break in 2005 was much later than the mean (Table 1/Figure 1), putting 2005 in the group of very late years. Leaf development then proceeded slowly during the cold May with 75% leaf development also occurring much later than the mean. As might be expected given the mild fall and very late frost, fall coloration and leaf fall in 2005 were also much later than the mean. However, combining all species, 50% leaf fall still occurred two days ahead of the extremely late timing of 50% leaf fall in 2002.
The extreme lateness observed in 2002 and now 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 considerably less variability in the timing of fall events. In fact, fall appears to be occurring later over the course of this study while spring shows great variability but no trend. These observations point out the need for long-term data sets and emphasize the importance of temperature in regulating these events.
- Research Category: Forest-Atmosphere Exchange
Physiological Ecology, Population Dynamics, and Species Interactions
