IEEE Spectrum - North American - March 2015 - 38

World
of Woven

tree s
Harvard Forest hosts scores
of research projects, some
of which go on for decades

phenocams
Six cameras shoot images at
30-minute intervals during
daylight hours. The hundreds of
thousands of photos captured
are used to create a "greenness
index" of the forest. The cameras
can determine the precise
biological beginning of spring
and autumn to within a day.
eddy flux tower
Installed in 1989, the tower is
30 meters high and located
1.7 kilometers from forest
headquarters. It provides the
world's longest continuous
record of net ecosystem carbon
dioxide exchange, evaporation,
and energy flux between the
atmosphere and the forest.
Individual sensors measure the
air multiple times a second, and
the gas exchanges are recorded
at hourly intervals.

weather station
The station measures air
temperature, relative humidity,
precipitation, incoming and net
radiation, barometric pressure,
wind speed and direction, and soil
temperature every 15 minutes.
Hydrological stations record
stream discharge and water
temperature at four stream
sites, and water level and water
temperature at two wetland sites.
A pressure-sensitive "snow pillow"
measures the rate of snowfall and
the water content of the snow pack
over the winter.

ant warming
An open-top chamber simulates
warming from a change in climate
of between 0.5 °C and 5.5 °C. The
annual heating and electricity costs
are $50,000. Ants are sampled
every month to see which species
thrive and which leave or die off.

One of the very first LTER experiments used underground
cables to heat a few hundred square meters of the forest floor
to five degrees centigrade above ambient (a temperature gain
that we may face late this century). The goal was to study how
the heat affected the amount of carbon dioxide released by the
microbes. Understanding this process matters hugely because
soil microbes already release nearly 10 times as much carbon dioxide each year as human activity does. The researchers discovered that the microbes in the soil at first released
more carbon dioxide than before. But as the years passed,
emissions fell again as the microbes adjusted to the warmth.
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acoustic mapping system
Three $100 devices monitor audio
in the forest: bird, animal, and
insect life, as well as tree falls
and human activity. Devices use
Raspberry Pi hardware running
Linux and include Wi-Fi and a
microphone that samples audio
at 24 kilohertz. Data is streamed
continuously to remote hard drives.
Future plans include algorithmic
identification of individual bird and
insect species.
hurricane-manipulation
experiment
In 1990, the experiment simulated
a large hurricane in a 0.8-hectare
(2-acre) forested area by pulling
down trees with a large winch.
Researchers have studied the
regrowth of tree species since
then, as well as the response of the
forest ecosystem to a catastrophic
storm. Such hurricanes have
traditionally occurred only every
50 to 200 years, but that could
happen more frequently with
climate change.

megaplot
This 35-hectare plot of the forest
precisely maps woody stems
over 1 centimeter in diameter-
more than 116,000 stems in
total. It is part of the Forest Global

Earth Observatories, a project
of the Smithsonian that tracks
the function and diversity of over
6 million trees in 24 countries
around the world. Harvard Forest
is one of the first temperate forests
in the project. It will remeasure the
trees every five years.
hemlock removal
Researchers simulated the arrival
of the invasive Asian woolly adelgid
bug by deliberately killing hemlock
trees in 6.5 hectares of the forest.
Within the next 10 years, wild
hemlock trees are predicted to die
off completely in the United States.
The study monitors the impact
on native wildlife by regularly
assessing each woody stem that's
at least 30 cm long, for browsing
by moose, porcupine, and deer.
predicting ragweedallergy hot spots
A three-year field survey gathered
data on pollen from 1,250
specimens of common ragweed,
a species that causes hay fever.
Expected outcomes include better
predictive tools and maps for
forecasting allergy hot spots, as well
as models of how climate change
affects human exposure to pollen.

detritus input and
removal treatments (dirt)
Researchers study forest soil by
measuring respiration, nutrient
leaching, and various chemical
properties. Results last year
suggest that sequestering carbon
in forest litter (to offset burning
fossil fuel) is probably not practical.

Tall trees are harder to heat up. Pamela Templer, an associate professor at Boston University, decided to start at the
roots, in a project that's testing the counterintuitive notion
that a warming environment might mean colder soils. The
U.S. Northeast's famous winter storms deposit a blanket of
snow early in the winter that insulates the ground from frigid
air later on. As temperatures rise in years to come, climate
models predict less snow but still freezing temperatures.
To simulate this, Templer's team shoveled away the first
snows from beneath 12 red oak and 12 red maple trees at
the Harvard Forest. They then fitted | co nti n u e d o n pag e 59
illustrations by

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