Why Phenology

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Why Phenology?

• Sensitive indicator of terrestrial vegetation
  responses to climatic variability
• Important component of global models
• Growing season in northern latitudes appears to
  be lengthening
• Educational value

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1. Developing a Phenological Model
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Growing Season Variability in Global Carbon
Models

• Simulated growing season length varies from five
  to ten months
• Need to establish realistic and consistent
  methods of regulating the timing and length of
  the growing season

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Step One

• Satellite Observations

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Data Set

• U.S. Advanced Very High Resolution Radiometer
• 1990-1992 daily observations
• 20 km x 20 km contiguous land cover sites
• Extracted deciduous broadleaf forest and
  grassland sites

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Step Two

• Meteorological Interpolation

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Weather Station Distribution
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1990
1990 1991 1992
deg C
deg C
gt32
lt-2
gt2
lt5
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1990 1991 1992
cm
cm
gt300
lt5
lt-30
gt30
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Step Three

• Model Development and Results

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Development Method

• Select a meteorological model that best predicts
  the satellite observations
• Traditional phenological models thermal
  summations, daylength, and drought stress
• Parameter selection based on iterative
  cross-validation procedure

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Phenology Model Summary
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DBF Onset
DBF Offset
Grassland Onset
Grassland Offset
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2. Growing Season Influences on Ecosystem
models
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SITE DISTRIBUTION
Mean Ann Temp
7.8
C
9.4C
11.8C
16.3C
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Growing Season Length vs. Mean Annual Temperature
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Charleston, SC
Burlington, VT
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3. The Need for Field Data
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Ground Measurements

• Hubbard Brook and Harvard Forest LTER phenology
• Onset 30 leaf expansion
• Offset initial canopy senescence
• Inconsistent methodologies

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Comparison of Observed and Modeled Phenology
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Ground monitoringmethods at the Jornada LTER
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Jornada Transitional Site
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Site of Near-death Experience
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Effects of Increased Sample Size on sample
standard deviation
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Instrument Intercomparison
FT FG PAI LAI
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Science Education (creative data-gathering)

• Global Learning and Observations to Benefit the
  Environment (GLOBE)
• Students measure budburst of local dominant
  species
• Useful for interpretation of satellite data
• Easily observable demonstration of
  climate-vegetation connection

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Conclusions

• Phenology is one of the most important topics in
  climate change research
• Next generation of satellites - MODIS - will
  bring unprecedented ability to monitor growing
  season dynamics
• Future topics include health and economic
  implications
• Excellent field for internet-based student
  involvement

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