The Phenology Handbook - USA National Phenology Network

visit a natural landscape can track green-up on a daily or weekly basis.
By identifying which habitats and plant species are leafing out, we can
identify the phenological events and species that contribute most to the
infrared reflectance values observed from space (this process is called
“ground-truthing”).
At an even finer spatial scale (e.g., from square miles to square meters),
biogeochemical sensors can measure daily and seasonal fluctuations in
temperature, precipitation, atmospheric gasses, sunlight, soil nutrients,
stream flow, and other components of the abiotic environment that
plants and animals require for growth. With these data on hand, scientists
can determine the influence of environmental factors on phenological
patterns.
The longest known phenological
monitoring record comes from
the Royal Court of Kyoto in Japan,
where the onset of flowering for
cherry trees has been recorded
since 705 AD. Some wine-producing
regions in Europe also boast
records of blooming and harvest
dates that extend back hundreds
of years.
SUMMARY
Over the long-term, the timing and duration of green-up can be compared from year to year and from decade to
decade to detect whether climatic variation affects the productivity or geographic distribution of natural plant
communities. Scientific disciplines can be combined to investigate phenological patterns across both biological
and geographical levels of organization. This integrated phenological research can provide layers of information
across space and time that reveal when and how different communities and biomes change as a function of climate
change and other environmental conditions. Although remotely-sensed data can provide broad measures
of global phenological patterns, ground truthing and biogeochemical monitoring are essential for identifying the
factors that drive phenological patterns within and among communities and biomes. Synthesizing information
from multiple levels of biological and geographical scales is the best way to discover broad ecological patterns
and the processes that drive them.
In the following sections of this handbook, we will help you to develop the botanical tools and record-keeping
methods needed to become an independent Phenology Steward who can contribute to the National Phenology
Network’s growing community of ground-truthers.
Green-up refers to the progressive increase in plant growth at the beginning of spring. Springtime increases
in plant growth can be tracked with great sensitivity by satellites, detecting and measuring the rate at which
the earth’s vegetation produces its annual flush of leaves. From a weekly series of satellite images covering
the Northern Hemisphere during the spring months, scientists can see that spring starts earlier at southerly
latitudes and progresses northwards, and spring starts earlier at lower elevations and progresses upward in
elevation. Intuitively this should make sense to many people – spring comes earlier in Southern California
than it does in Northern California, and spring comes earlier in the valleys than it does in the mountains. Of
course the intricate details of this pattern depend on the topography of the land as well as many physical,
chemical, and biological factors, but the broad geographic patterns are simply remarkable: when reviewing
the series of satellite images, it appears to scientists as though a green wave is progressing northward in
latitude and upward in elevation! (In the Southern Hemisphere, the green wave progresses southward in
latitude and upward in elevation).
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