Newsletter

Volume 9, Number 6
November-December 1992

Director’s Note

When the Institute of Ecosystem Studies was
created in 1983, one of its principal goals was
“to establish and maintain long-term,
experimental and reference studies of
ecosystems”. The worth of long-term
ecological research already was recognized
from a number of investigations, including
the Hubbard Brook Ecosystem Study that had
been gathering data on air-land-water
interactions since 1963 (and continues to do
so). With the formation of the Institute of
Ecosystem Studies, sites in forests, fields and
streams across the Mary Flagler Cary
Arboretum were established as long-term
research plots.

Now, almost a decade later, data continue to
be collected, baseline information against
which scientists and educators will be able to
measure change for years to come. Some of
these data now are being incorporated into a
new long-term project. Forest Responses to
Stress and Damage, described in the cover
story of this issue of the lES Newsletter.

The lES Newsletter is published by the
Institute of Ecosystem Studies at the Mary
Flagler Cary Arboretum. Located in
Millbrook, New York, the Institute is a
division of The New York Botanical
Garden. All newsletter correspondence
should be addressed to the Editor.

Gene E. Likens, Director
Joseph S. Warner, Administrator
Alan R. Berkowitz, Head of Education

Editor: Jill Cadwallader
Printing: Central Press

INSTITUTE OF ECOSYSTEM STUDIES
The New York Botanical Garden
Mary Flagler Cary Arboretum
Education Program
Box R

Millbrook, NY 12545
(914)677-5359

Stresses and Change
Forests

The composition of our forests is changing.
Flowering dogwood trees in wooded areas
have experienced a 96% decline over the
past decade because of a fungal infection.

The wooly adelgid, a tiny sucking insect, is
slowly killing hemlocks. Chestnut oaks are
dying, probably from repeated attacks by
the gypsy moth, while data from long-term
research plots at the Arboretum show that
the densities of some species, for example
the chestnut, are increasing.

Natural changes occur constantly in
ecosystems. In these times of increasing
human impact on the environment,
however, changes may be accelerated, and
they are not always natural. In order to
know when changes are occurring, to try to
understand the reasons for these changes
and to make predictions regarding the
future status of ecosystems, routine
monitoring is essential.

Recognizing the need for an integrated
approach to monitoring Hudson Valley
forests. Institute ecologists Drs. Gary M.
Lovett, Charles C. Canham, Clive G. Jones
and Richard S. Ostfeld developed
FORSTAD — Forest Responses to Stress
and Damage. This long-term monitoring
program was in the planning stage for
several years before field sampling began in
March 1991. With a number of potential
agents of environmental stress to consider,
the ecologists chose to focus their attention
on the forest’s responses to insect out-
breaks, air pollution and climate change.

The FORSTAD team is interested espe-
cially in linking ecosystem components to
the whole system, to learn what stress or
damage to individual trees might do to the
entire forest. For example, when an oak tree
is damaged by gypsy moths, are forest
functions such as nutrient cycling affected?
Then, if that oak dies, does the same
species take its place or do new species
move in, and how does the forest change as
a consequence?

While the goal of FORSTAD scientists is to
establish forest monitoring sites throughout
the Hudson Valley, the early focus of the
project is the development and refining of
sampling methods and the establishment of
research plots at the Arboretum. Monitoring
sites are located primarily along the sides of
the Cannoo Hills, in typical upland forest
dominated by oak, hickory and maple trees.
Some of the plots are part of previously
established long-term research projects, so
more than 10 years of vegetation and gypsy
moth population data are already available
for integration with new FORSTAD
measurements. In the vegetation plots, data

in Hudson Valley

on species of trees, their size, which
individuals have died and what new ones
are growing will continue to be recorded at
regular intervals. Against this background,
other measurements also will be made.

FORSTAD research assistants Christopher Borg
(left) and Michael Miller measure and perma-
nently mark trees in the long-term vegetation
plots on the Arboretum. (The white coveralls
help Institute staff find any deer ticks that they
might pick up.)

Understanding Forest Stress

The gypsy moth is an introduced pest that
has become a major cause of forest stress
and damage in the Northeast. To date, there
is neither a clear understanding of what
causes gypsy moth outbreaks nor a reliable
means of predicting defoliation. Data on
egg mass densities and episodes of defolia-
tion have been collected at 20 Arboretum
sites since 1981. Observations will continue
at the existing long-term sites, and data also
will be collected across all other
FORSTAD plots, on numbers of egg
masses, larval instars (stages of develop-
ment between molts) and pupae, as well as
on degrees of defoliation.

In the course of the Institute’s long-term
gypsy moth studies, it was found that
increases in the population density of these
insects coincided with declines in small
mammal populations, suggesting that
animals such as the white-footed mouse
may be important predators of moth larvae
and pupae. As part of FORSTAD’s

continued on page 2

FORSTAD, from page 1

monitoring program, live-traps are set out
for short periods during spring, summer and
fall to estimate population sizes of white-
footed mice, chipmunks and other small
forest mammals. Data will be used to
confirm the correlation between small
mammal and gypsy moth populations as
well as for other studies. Small mammals
have an impact on tree reproduction, for
example — their diet is primarily seeds, so
an increase in their numbers can lead to a
decrease in seed survival and eventually to
a reduction in numbers of new trees.

Gaseous nitrogen, N^, is converted to usable
compounds by natural processes occurring
in the atmosphere or soil. Ths “fixed”
nitrogen may be used over and over again
by plants, animals and microbes in cycles
of growth, death and decomposition.
Combustion of fossil fuels (for instance, in
automobiles or power plants) increases the
rate at which nitrogen gas is converted to
usable forms and deposited to the bio-
sphere. The nitrogen occurs as nitrogen
dioxide (NO^) or nitric acid gases, as
particles, or dissolved in raindrops (as one
of the acids in “acid rain”). Deposition of

10,000

— o—

Unbanded Teahouse

Banded Cannoo

- D ^

Unbanded Cannoo

CARY ARBORETUM, NY

1 1 —

1981 1982 1983

1984

1985 1986

YEAR

1987 1988 1989 1990 1991

One example of long-term cycling in a forest ecosystem is illustrated by this graph of numbers of gypsy
moth egg masses. Data collected from forested sites on the Arboretum’ s Cannoo Hill and Teahouse
Hill show peak levels in 1981 and in 1990. The downward part of the cycle now has begun again.
(‘Banded” and ‘Unbanded’ refer to a sampling method in which burlap bands are tied around some
trees.) Graph prepared by research assistant Michele P. Richard

Data gathered on small mammals also will
contribute to lES studies on the ecology of
the deer tick, the carrier of Lyme disease.
Numbers of white-footed mice are of
particular relevance because these animals
are reservoirs for the disease-causing
bacterium. The ticks themselves will be
identified and counted before host mam-
mals are tagged and released. To comple-
ment these data, FORSTAD scientists are
using a technique known as “tick drag-
ging”: questing ticks will be collected on a
square of white cloth dragged along
transects in the research plots. Taken to the
lES laboratory, the tiny arthropods then can
be examined microscopically for the
presence of the Lyme disease bacterium.

There are also climatic and air pollution
stresses to the forest, and one way in which
these stresses may affect the ecosystem is
by altering the nitrogen cycle. Nitrogen (N)
is a nutrient, an element that is essential for
the growth and development of all living
organisms. Like other nutrients, nitrogen
recycles constantly through the biosphere

nitrogen in our area has increased approxi-
mately tenfold since pre-industrial times.
This has increased the amount of nitrogen
cycling in forest ecosystems, but the effect
of this increase on forest health is still a
matter of research and debate.

To learn how increases in nitrogen deposi-
tion have changed nitrogen cycling and the
health of our forests, the FORSTAD team
has established two nitrogen cycling plots
to monitor levels of nitrogen in water, soil
and trees. The chemistry of throughfall, or
the water dripping from the trees, and of
water in the soil (collected by a suction
device) as well as of leaves is being
analyzed. The rate of cycling of nitrogen
from the plants to the soil is measured by
collecting and analyzing the annual leaf
fall. The rate of nitrogen mineralization, or
how fast the element becomes available for
uptake and use by plants, is determined by
incubating a sample of the forest floor in
the laboratory and measuring the change in
available nitrogen over a two-week interval.

In addition, FORSTAD ecologists have
access to a long-term database from the
Institute’s Meteorology and Air Quality
Station, a facility that provides continuous
measurements of precipitation chemistry
(e.g., acid rain) and amount, air tempera-
ture, wind speed, wind direction, relative
humidity, solar radiation, and atmospheric
concentrations of ozone, sulfur dioxide,
nitric acid vapor and fine aerosols. The
scientists currently are developing and
testing methods for nitrogen dioxide
measurement as well.

Some might expect that with increased
nitrogen deposition from the atmosphere
there would be a corresponding increase in
plant growth, due to a “fertilizer effect”.
This generally has not been observed in
Hudson Valley forests, for reasons that are
not yet clear. Normally almost all the
nitrogen deposited in a forest is used up in
normal plant or microbial growth processes,
or is tied up in non-decomposing com-
pounds in the soil. It is possible that trees
that have evolved over the millennia in an
environment where nitrogen is a scarce
resource cannot deal with sudden nitrogen
excesses. The consequences for the trees
may be nutritional imbalances for individu-
als or shifts in competition between species.
If the trees or microbes cannot use all the
nitrogen being deposited, the excess may
leach out into streams, lakes and groundwa-
ter. By monitoring nitrogen levels and
observing forest health over time,
FORSTAD ecologists hope to learn what
might be happening. (It has been discovered
recently that nitrate — another nitrogenous
compound — is leaching out of forest
watersheds in the Catskill and Adirondack
Mountains. Since nitrates in drinking water
pose a potential health threat [see story on
page 3] this is a question that Dr. Lovett is
pursuing in another ongoing lES project.)

By correlating their observations of
atmospheric deposition, forest chemistry,
tree populations and insect and mammal
species, Drs. Lovett, Canham, Jones and
Ostfeld will develop ecosystem “models”

— mathematical formulations of essential
relationships between components of the
forest ecosystem. These computer simula-
tions will help the ecologists understand
how the ecosystem works and make
predictions about the effects of continued
stresses to forests.

This research is funded through a grant to
the Institute of Ecosystem Studies from the
General Reinsurance Corporation.

Dr. Boyer Studies Path of Groundwater Pollutant

A casual observer might guess that Dr.
Joseph Boyer is a geologist rather than the
microbial ecologist that he is. Soil maps of
the Arboretum and surrounding areas are
spread out on his desk in the post-doctoral
scientists’ laboratory, and when he
identifies likely sites he packs his soil auger
and sets out to take core samples. The
information he is looking for with these
geologist’s tools, however, will help to
answer important ecological questions
about why nitrate (NO3 ) collects in soil and
how it can be prevented from contaminat-
ing groundwater.

As described in this issue’s cover story,
nitrogen is an important part of the global
ecosystem. Nitrogen gas makes up nearly
80% of the Earth’s atmosphere and
combines naturally with oxygen or
hydrogen to make other chemical com-
pounds. While these compounds are used
by living organisms in the growth process,
at high levels they can have detrimental
effects. Nitrate, for example, becomes a
potential problem when present in high
concentrations in drinking water — upon
entering the gastrointestinal tract, it is
converted to nitrite, which enters the
bloodstream and competes with oxygen for
binding sites in hemoglobin molecules.

This condition, called methemoglobinemia,
can lead eventually to suffocation; infants
who suffer from it are called “blue babies’’.

Major sources of nitrate in agricultural
areas are commercial fertilizers and animal
wastes. Dr. Boyer and another microbial
ecologist at the Institute, Dr. Peter
Groffman, are particularly interested in the
nitrate that rain washes down through the
soil into aquifers ... underground water in
rock, sand or gravel. Dr. Boyer hopes to
develop ways to keep nitrate out of the
groundwater, thereby not only assuring
better quality drinking water but also
minimizing the loss of valuable nitrogen
from agricultural fields.

Once nitrate is in groundwater, engineering
options for clean-up are limited and costly.
Dr. Boyer is investigating another ap-
proach, denitrification — a naturally
occurring process in which nitrogenous
compounds are converted to harmless
nitrogen gas — as a solution to the problem
of nitrate build-up in groundwater.

5C + 4NO3 + 2Hp = 2N3 + CO2 + 4HCO3

carbon + nitrate + water =

nitrogen gas + carbon dioxide gas + bicarbonate

Denitrification (represented chemically
above) is the work of bacteria living in the
soil, and because it is an anaerobic process
— one that occurs in the absence of oxygen

— it can occur deep underground. Under
normal conditions, almost all excess soil
nitrate is converted by this process.
However, when nitrate levels are high due
to the effects of agriculture or other causes,
denitrification does not happen fast enough
and some nitrate escapes from the soil into
the groundwater.

therefore is carried rapidly to deeper soils.
How does the amount of carbon in the soil
relate to current and historical land use?
Whereas forest soils receive nutrients from
decomposing plant material, agricultural
soils often do not because much of the plant
material is removed during harvest. Is there
a difference in available carbon levels
between forest and agricultural soils?

Dr. Joseph Boyer uses a soil auger to collect soil samples in
different land use areas. He is comparing forested and agricultural
sites to learn what factors affect denitrification.

While some forms of carbon
are easy to use (like the
sugar, glucose) others are
not. During the degradation
of plant litter, the easy-to-
use forms are used first, and
the remaining humic acids
end up in soils and are
broken down at an as-yet-
unknown rate. Dr. Boyer
will be investigating carbon
sources in the soil to learn
how they affect the
denitrification process.

Where does the carbon used
by denitrifying bacteria
come from? Is it material that has been in
the ground for years? Or is it from recently
decomposed organic matter, washed down
through the soil by the rains? How is it
distributed through the soil column? Is it
concentrated at the surface and therefore
not available at the groundwater level?

This is of potential relevance because
nitrate dissolves easily in water and

* On the logarithmic pH scale ofO - 14,
very acidic materials have a value at the
low end of the scale — the pH of lemon
juice is approximately 2 — while very basic
ones are at the high end of the
scale — ammonia has a pH of 11.)

historical land use and taking samples to
identify similar soil types in different land
use areas; by selecting present and former
forest and farm sites with the same
geological origins, he will eliminate soil as
a variable in his investigations. The soil
type that he seeks is glacial outwash, whose
well-sorted material provides good drainage
with water percolating in a relatively
straight path to the groundwater. He will
analyze soil cores taken from surface to
water table to determine the carbon source
for the groundwater denitrification process.

Fortunately for Dr. Boyer, certain plant
materials have distinctive carbon isotope

continued on page 4

What factors control denitrification? As
stated, the process requires low oxygen
levels and thus cannot occur
near the soil surface. The
pH, or the level of acidity or
alkalinity, must be neutral

— approximately 7 or 8*.

Soil temperature is a factor
too, with the rate of
denitrification doubling for ,

every increase of 10°C (just J'

less than 20° F). Nutrients
and trace metals are
required for the bacteria to
grow, while the presence of
some chemical compounds

— sulfide, for example —
may inhibit denitrification.

Finally, and of particular
interest to Dr. Boyer, is the
source of the carbon
required for the chemical
reaction to occur.

Dr. Boyer is consulting soil maps, studying

Groundwater, from page 3

ratios (isotopes are atoms of the same
element with different weights). Most forest
plants in this area — deciduous trees,
shrubs and pines — have one ratio, while
certain agricultural plants such as com have
another. Since “you are what you eat”, by
analyzing the carbon isotope ratios of
denitrifying bacteria and the COj produced
by their respiration. Dr. Boyer will be able
to determine which sort of plant was the
major food source for the bacteria. In sites
where the source of new soil carbon differs
from historical sources (e.g., forests
growing on old com fields), the carbon
isotope ratio will help him distinguish
whether the bacteria are using new or old
carbon. This, in turn, will help him
understand how carbon availability might
limit microbial activity in soil, knowledge
that is key for developing strategies to
increase pollutant removal from groundwa-
ter.

Dr. Joseph N. Boyer joined the Institute’ s
scientific staff in October. With a doctorate
in marine science from the Virginia
Institute of Marine Science, College of
William and Mary, he has taught at East
Carolina University in North Carolina, has
been involved in the design and implemen-
tation of water reuse systems for aquacul-
ture, and has been an environmental
consultant. Dr. Boyer is at the Institute on a
two-year postdoctoral appointment funded
by a U.S. Department of Agriculture grant
awarded to Dr. Peter M. Grojfman.

INSTITUTE OF
ECOSYSTEM STUDIES
The New York Botanical Garden
Mary Flagler Cary Arboretum
Education Program
BoxR

Millbrook, New York 12.545-0178

Newsletter

Winter Calendar

CONTINUING EDUCATION PROGRAM
Winter and Spring Semesters

The winter semester begins in mid-January.

Free catalogues describing classes, workshops
and ecological excursions offered during winter
and spring are available from the Gifford House.
Call the number below for information.

SUNDAY ECOLOGY PROGRAMS
Free public programs are held on the first and
third Sunday of each month, except over holiday
weekends. Programs begin at 2 p.m. at the Gifford
House on Route 44A unless otherwise noted. Call
(914) 677-5359 to confirm the day’s topic.

Jan. 17: Earthworm Investigations, an indoor
program for young people, ages 6-12, and their
parents, led by Kass Hogan
Feb. 7; Diatoms: Microscopic Jewels in Aquatic
Food Webs, a walk and demonstration led by
Dr. R. Jan Stevenson

Feb. 21: Update on Zebra Mussels in the Hudson
River, a slide presentation by Dr. David Strayer
Mar. 7: Gaia Theory: Wake-up Call for
Humanity!, a slide presentation by Dr. William
Shaw

• In case of inclement weather, call (914) 677-
5358 after I p.m. to learn the status of the day’ s
program. For outdoor programs, dress for the
weather conditions, with sturdy waterproof shoes.

lES SEMINARS

The Institute’s program of scientific seminars
features presentations by visiting scientists. Free
seminars are held at the Plant Science Building on
Fridays at 3:30 p.m.

Jan. 15: Remote Sensing of Ecosystem Processes
in Grasslands, by Dr. Clarence Turner, Kentucky
State Univ.

Jan. 22: The Application of a Geographic
Information System to Watershed Modeling, by
Dr. Paul Barten, Yale Univ. School of Forestry
Jan. 29: Elevated Atmospheric COj and
Feedbacks Between Carbon and Nitrogen
Cycling in Terrestrial Ecosystems, by Dr. Don
Zak, Univ. of Michigan

For more information, call (914)

Feb. 5: The Socioecology of Density-Dependent
Competition, Infanticide and Dispersal in a
Fluctuating Environment, by Dr. Jerry Wulff,

U.S. Environmental Protection Agency, Corvallis,
Ore.

Feb. 12: Intra- and Inter-ecosystem Comparisons
of Nitrogen Cycling Using Network Analysis, by
Dr. Robert Christian, East Carolina Univ.

GREENHOUSE

The lES greenhouse is a year-round tropical plant
paradise as well as a site for controlled environmen-
tal research. The greenhouse is open during
Arboretum hours. Admission is by free permit from
the Gifford House.

GIFT SHOP

Senior Citizens Days: On Wednesdays, senior
citizens receive a 10% discount (except sale items).
January Sale: Most holiday items and calendars
half price; 20% off most gifts, 10% off most books.

ARBORETUM HOURS
(Winter hours: October I - April 30;
closed on public holidays)

Arboretum grounds are open Mon. - Sat.,

9 a.m. - 4 p.m.; Sun. 1 - 4 p.m. (Trails and internal
roads may be closed when snow-covered or icy.)
The Gift and Plant Shop is open Tues. - Sat.,

1 1 a.m. - 4 p.m. and Sun. 1 - 4 p.m.

(Closed weekdays from 1 - 1:30 p.m.)

• All visitors must obtain a free permit at the
Gifford House Visitor and Education Center on
Route 44 A for access to the Arboretum. Permits are
available until 3:00 p.m. daily.

MEMBERSHIP

Become a member of the Mary Flagler Cary
Arboretum. Benefits include a member's rate for
lES courses and excursions, a 10% discount on
purchases from the Gift Shop and a free subscrip-
tion to the lES NEWSLETTER. Individual
membership is $30; family membership is $40. For
information on memberships, contact Janice
Claiborne at (914) 677-5343.

677-5359 weekdays from 8:30-4:30.

Nonprofit Org.
U.S. Postage
PAID

Millbrook, N.Y.
Permit No. 16

Volume 9, Number 6
November-December 1992

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