Newsletter

Volume 4, Number 5
September - October 1987

At the Arboretum ...

This summer the Cary Pines Trail was
extended. The new loop trail winds
through a lovely hemlock forest over-
looking the East Branch of the
Wappinger Creek.

[Ed. note; Due to storm damage,
Arboretum trails are temporarily
closed.]

Sign up now for special landscape design
workshops.

Sunday Ecology Programs are held on
the first and third Sunday of each month
(except holiday weekends).

^ ^ ^

See the Fall Calendar on the last page of
this Newsletter for information on all of
our current public programs.

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
Design and Printing: Central Press

INSTITUTE OF
ECOSYSTEM STUDIES
The New York Botanical Garden
Mary Flagler Cary Arboretum
Box AB

Millbrook, NY 12545
(914) 677-5343

Cary Summer Fellowship:
Plant Invasion of Old Fields

When a field is abandoned - no longer
needed for crops or as pasture - it will be
invaded by woody plants. This replace-
ment of herbaceous plants by shrubs and
trees happens at different speeds in
different parts of a field. Succession -- one
of the most important processes in ecol-
ogy “ is the way in which this woody
invasion occurs. Dr. Juan Armesto was
awarded a 1987 Cary Summer Fellowship
to study the process of succession in
collaboration with lES Plant Ecologist Dr.
Steward Pickett.

Dr. Armesto is a professor of botany and
plant ecology at the University of Chile in
Santiago. His research into the dynamics
of plant communities usually takes him to
the temperate rain forests of Chiloe, a
mountainous island off the southern coast
of Chile where the climate is much like
that of the U.S. Pacific Northwest. There
he looks at the changing forest structure -
more advanced stages of succession - to
understand the dynamics of a forest. The
data from his observations are useful in
making predictions of how forests develop
and change, and these predictions in turn
help managers and the public understand
how forests can be utilized without being
destroyed forever.

Dr. Armesto received his Ph.D. at Rutgers
University, where he began to study the
process of woody species invasion into
abandoned agricultural fields. His
research colleagues were Dr. Pickett and
Dr. Mark McDonnell, a terrestrial
ecologist at lES. The Cary Summer
Fellowship provided an exciting
opportunity to examine different aspects
of the invasion process using existing
information on the history of Arboretum
Oldfields. For three months this summer
Dr. Armesto devoted his time to studying

the upland fields near the Greenhouse. He
was concerned with the question of what
factors might influence the spatial
distribution of “hot spots" for plant
invasion in those fields.

To learn the answer to that question he set
up plots within two areas, one a recently
abandoned hay field (mowed until 1982)
and the other a former pasture abandoned
since the late 1930’s. In each area he put
transect lines from reference features,
such as the edge of the woods, to the
middle of the field, and randomly selected
0.5m X 2.0m sampling plots along those
lines. Wearing a long-sleeved shirt and
gloves to ward off poison ivy, brambles
and similar hazards, he counted the
number of species in each plot. (Much to
the surprise of any casual observer, a total
of 65 different species of higher plants was
found in the research plots of what
appeared to be a homogeneous hay field!)

Dr. Armesto also calculated the area of
ground cover in each research plot, listed
the species, and ranked them by
abundance. The information on the
number of species per plot (i.e. the species
richness) was used to generate a map of
the hay field on a computer. The result,
below, looks like a topographic map, and
shows the distribution of species richness
in the field as contour lines which connect
points with the same richness. More
species were found in areas of the field
that were close to the wood’s edge,
indicating that this edge is a major feature
affecting species invasion.

Contour Lines of Species Richness

Number of plant species in a recently abandoned
hay field, illustrated by contour lines. Figures on
the sides are distance in meters.

Data from the field abandoned in the
1930’s showed two influences on the
process of succession there. One was ‘the
forest edge effect’, as described in the
preceding paragraph. This resulted in
rapid establishment of woody patches due
to seed dispersal and root sprouting from

continued on page 4

Autumn’s Strategy: Senescence and Abscision

by Kerry Bauman, Summer Project Assistant

The season is turning: a hint of coolness,
shadows stretch long in the late
afternoon, sky darkening earlier each
night. These subtle, almost
imperceptible changes are sufficient to
spur a myriad of alterations and activities
in preparation for winter. Perhaps the
most conspicuous of these alterations in
mixed-deciduous forests of the
Northeast is autumnal leaf-fall. This
process involves leaf senescence and
abscision.

The term abscision is derived from the
Latin and means, literally, to separate a
member from the whole using an
external force. While abscission in plants
is considered an internal, physiological
action of the plant, the surrounding
environment is involved. Shorter day
lengths and lower temperatures affect
the relative balances of chemicals within
a leaf. These alterations initiate
processes that cause senescence (aging)
and, ultimately, abscision.

The most visible symptom of leaf
senescence is changing leaf color. A
healthy leaf contains several kinds of
pigments that are essential for
photosynthesis, the process by which
plants use light energy to convert carbon
dioxide and water into carbohydrates.
Chlorophylls a and b are two of these
pigments, as are carotenoids and
anthocyanins. Each pigment absorbs
light of particular wavelengths in the
visible spectrum, and reflects those
wavelengths of light which it cannot
absorb. It is this reflected light that we
see as color.

Healthy leaves appear green because
they have an abundance of chlorophyll.
Chlorophyll absorbs violet, blue, orange,
and red wavelengths of light, and reflects
green and yellow wavelengths. During
senescence, chlorophyll production
decreases dramatically, while the normal
breakdown, or catabolism, of chlorophyll
does not decrease. Thus there is a net
loss of chlorophyll from the senescing
leaf. In the absence of chlorophyll, other
pigments become visible. It is the
yellows and oranges reflected by
carotenoids and reds reflected by
anthocyanins that we recognize in the
brilliant foliage of deciduous trees in
autumn.

One of the important functions of
senescence is the mobilization of
materials within a leaf. Some of the
catabolites, breakdown products which

are primarily nutrients, are transported
from the senescing leaf to areas of the
plant where they are needed or stored.
Nutrients that remain in the leaf when it
falls are not all lost, either. Some are
liberated to the soil during leaf
decomposition and can be taken up, with
water, by the plant’s roots. In this way,
senescence and abscision enable a plant
to effectively “recycle” available
nutrients.

The abscision zone of a leaf is an area of
undifferentiated cells typically located at
the point where a leaf’s stem joins the
branch. In a healthy leaf these cells
appear to be in a state of arrested
development ... they have weaker cell
walls and lack many of the specialized
components of regular plant cells. When
the leaf begins to senesce, chemical
changes occur which cause cells of the
abscision zone to differentiate, resulting
in leaf abscision.

The mechanism of leaf abscision varies
between plant species, but a generalized
version can be described. The actual
physiological processes of separation
occur in a narrow band of cells within the
abscision zone, called the separation
layer. A thin membrane, called the
middle lamella, cements adjoining cells
together. During abscision the cells of
the separation layer secrete enzymes
that cause the middle lamella to swell,
weaken, and eventually disintegrate,
leaving adjacent cells free. Protective
cells grow next to the separation layer;
quick development of this leaf scar is
beneficial to the plant because it
prevents invasion by insects and disease-
causing organisms.

In some plant species, instead of
separation occurring as a result of the
dissolution of the middle lamella, the
cells of the separation layer appear to
simply dissolve and the leaf falls. In still
others, the cells of the abscision zone
become suberized (transformed into
cork), cutting off water movement. The
leaf then dies and is left to twist in the
wind until it breaks off.

Leaf scars on tree branches provide clues
to the different processes of abscision.
When separation involves a rapid,
complete, chemical dissolution of the
middle lamella, the resulting scar is
smooth in appearance. When separation
occurs primarily as a physical breaking
away, the scar appears relatively rough.

Why does abscision occur? A plant
produces only as many fruits and flowers
as can be supported by its leaves, and
only as many leaves as can be supported
by its roots. In this manner, a plant
achieves a homeostasis, or balance, with
the resources available in its
environment. Numerous factors affect
this balance, including temperature
extremes, moisture stress (characterized
by low soil moisture and low atmospheric
humidity), wind, infection by disease or
pests, and pollution stress. If the
environment changes suddenly, it is to
the plant’s advantage to change
accordingly. Abscising leaves is one
means of maintaining homeostasis.

In the seasonal climate of the Northeast,
it is advantageous for some plants to
drop their leaves when winter brings
unfavorable growing conditions. In this
way they conserve resources until
favorable conditions return in the spring
and summer months. The brilliance of a
mixed-deciduous forest in autumn is a
dramatic manifestation of this abscision
strategy.

ILLUSTRATIONS BY LISA H. BANDAZIAN

New Staff

LAURY ZICARI, research displays
coordinator, joined the lES Education
Program staff at the beginning of
September. She is developing display
materials to accompany research demon-
strations at the Arboretum, and will be
coordinating public education programs
related to these demonstrations. Ms.

Zicari has a master’s degree in forest
ecology from the SUNY College of
Environmental Science and Forestry at
Syracuse. Among her previous accom-
plishments was the design of an “Eco-Van”
for the Environmental Education Outreach
Facility at the Schuylkill Nature Center in
Philadelphia.

Promotion

JOHN OLSON has been promoted to
senior gardener. Mr. Olson began
permanent employment as a gardener at
the Mary Flagler Cary Arboretum in
January, 1973, and currently works with
Manager of Display Gardens Bradley
Roeller in grounds maintenance and
horticulture.

Summer Staff at the Institute

During the summer months high school and college
students are hired to assist on research projects and to
work with operations and display garden staff. In
addition, graduate students and scientists from other
institutions come to our labs to advance their own
studies. This summer’s staff were;

Top:

Front row (left to right): Karen Souza (horticulture);
Beth Schroeder (horticulture); Claes Thelemarck
(vegetation dynamics/zooplankton); Diane Borden
(opossums/Lyme tick/coyote predation); Eileen
Geagan (air pollution effects on white pine)

Second row: Marc Steininger (gypsy moths); Lauren
Parmalee (acid rain study ponds); Karl Schoeberl
(invertebrates in Tivoli South Bay)

Third row: Paul Ode (interactions on utility rights-of-
way): Harold Fraleigh (interactions on utility r-o-w);
Rob Hossler (opossums in S.E. New York); Laura
Sices (nutrient uptake by pine seedlings); Amanda
Hiller (environmental chemistry)

Back row: Helen Cyr (aquatic ecosystems); Kerry
Bauman (pollution garden); Steve Baines (dissolved
organic matter in lakes); Dave Behrens (operations);
Dorothy Ansley (horticulture); Heather Henter (gypsy
moths)

Bottom:

Front row: Erik McCarron (algae in Wappinger
Creek); Alan Zytowski (operations); Richard
Lounsbury (Greenhouse); Geoff Lloyd (interactions on
utility r-o-w)

Back row: Judy Koch (interactions on utility r-o-w);
Mark Vose (precipitation & soil moisture); Keith Elliot
(operations); Hannah Morgan (Business Office);
Richard Pouyat (history, ecology of urban natural
areas)

Missing from photographs: Juan Armesto (old field
structure); Lauren Atherly (Business Office); Matthew
Eaton (air pollution effects on white pine); Amie Frind
(permanent vegetation plots, NYBG Forest); Jane
(jerlach (acid rain study ponds); Alan Goldhammer
(fluxes in Tivoli South Bay); William Gonzalez
(permanent vegetation plots, NYBG Forest); Jerry
Griffin (horticulture): Cheryl Hayashi (nutrient
budgets in Mirror Lake, NH); Lars Hedin (organic
matter in natural stream ecosystems); Andrea Kirn
(interactions on utility r-o-w); Greg Likens (computer-
ization of reprint collection); Leslie Likens (computer-
ization of reprint collection); Karin Limburg (feeding
ecology of river herring); Mark Mattson (Mirror Lake

sediments): Andrew McLaughlin (trail maintenance,
NYBG Forest); Cliff Ochs (bacterial production in
Mirror Lake); Chris Peterson (vegetation recovery,
Tionesta Natural Area); Cathy Snygg (scenic overlook,
NYBG Forest); Richard Spalding (meadow
management & trail displays); Sue Tipton (air

pollution garden & nature trails); Rachael Warner
(horticulture); Kathleen Weathers (cloud water
deposition; Todd Webber (vegetation sampling,
Tionesta Natural Area); Carl White (mineralization in
the NYBG Forest soils)

Invasion ... from page 1

the nearby woods. The second influence
was a stone wall separating the area from
an adjacent field. Scattered trees were
present along this wall at the time that the
field was abandoned. Those trees not only
produced seeds themselves but also
provided perches for fruit-eating birds that
dispersed seeds from different plant
species into the field. This led to the
growth of dense thickets of cedars,
dogwoods and sumac along the wall. Other
areas in the field, located away from the
forest edge and the stone wall, were still
dominated by grasses, 50 years after
abandonment.

Dr. Armesto is interested in regional
comparisions and will use data resulting
from this summer’s study to compare the
effects of land use between the eastern
United States, where fields have been
used for the past 200 to 300 years, and
southern Chile, where fields date from no
more than 100 years. In addition, he is
leaving his research plots at lES until next
year when he hopes that soil tests will
provide data on how nutrient levels and
other soil characteristics relate to the “hot
spots” for species invasion within old
fields.

9|( 9(( 9)c 9|(

The Cary Summer Fellowship is an annual
award enabling one or more scientists to
do research at the Institute. Funds for the
award are provided by the Mary Flagler
Cary Charitable Trust. Cary Fellows are
typically at an early stage in their scientific
careers, and the research position at lES
gives them the opportunity to pursue
intensive, uninterrupted research. Results
from these short-term projects contribute
to the scientists’ long-term teaching and
research programs at their home
institutions.

Fall Calendar

ADULT EDUCATION PROGRAM

Landscape Design Workshops

Oct. 31st: Landscape Site Plans: Interpretation
and Review

Nov. 14th: Landscape Preservation: Ecological
and Social Issues

Holiday Workshops

Nov. 7th and 21st: Large Wired Pinecone Wreath

Dec. 5th: Stenciled Tree Skirt

Dec. 5th: Berry Bowl Workshop

Dec. 12th: Williamsburg Centerpiece

Dec. 12th: Holiday Arrangement

For registration information, or to be put on the
mailing list for the Adult Education Program
catalogue, call the Gifford House at the number
below.

SUNDAY ECOLOGY PROGRAMS

Free public programs are offered on the first and
third Sunday of each month. All programs are from
one to two hours long, and begin at 2:00 pm at the
Gifford House unless otherwise noted.

Tentative schedule (please call (914) 677-5358 to
confirm the day’s topic):

Oct. 18: The secret life of soils (Alan Berkowitz) -
Walk

Nov. 1st: Return to the rain forest: Ecuador
expedition ’87 (Jill Cadwallader) - Talk
Nov. 15th: Air pollution and the forest (Gary
Lovett) - Walk

Dec. 6th: Unusual flora and fauna in Australia
(Gene Likens) - Talk

For ecology walks, wear long pants and sturdy
footwear with socks; long-sleeved shirts or jackets
are also recommended. In case of inclement
weather, call (914) 677-5358 after 1 pm to learn the
status of the day’s program.

Ecology talks are slide presentations held indoors at
the Gifford House.

RESEARCH DISPLAYS

lES is setting up displays to introduce Arboretum
visitors to the methods and thinking behind ongoing
ecological research projects. The first of these to be
completed is “Acid Rain Study Ponds”, behind the
Gifford House. Here, tanks simulating natural ponds
(complete with plants and animals) are exposed to
different chemical treatments and the results
recorded twice a week. This free demonstration is

open to the public during Arboretum hours through
October; children must be accompanied by an adult.
An lES staff scientist will give special programs to
groups that call the number below for an
appointment.

GREENHOUSE

The lES Greenhouse performs double-duty: it is a
year-round tropical-plant paradise as well as a site
for controlled environmental research. The public is
invited to explore both aspects during Arboretum
hours. There is no admission fee, but visitors should
first stop at the Gifford House for a free permit.

SCIENTIFIC SEMINARS

The Institute’s weekly program of scientific
seminars features presentations by visiting scientists
or Institute staff. All seminars take place in the Plant
Science Building on Fridays at 3:30 p.m. Admission
is free. For a schedule, contact Julie Morgan at
(914)677-5343.

ART EXHIBIT

“Whispering Spheres”, a series of oil paintings by
former Poughkeepsie resident Catherine Rutgers
Sand, is on display in the lobby of the Plant Science
Building. This exhibit is open on weekdays from
8:30 to 4:30 until December 11th (closed on public
holidays). Admission is free.

ARBORETUM HOURS

Monday through Saturday, 9 a.m. to 4 p.m.; Sunday,
1 - 4 p.m. The Gift and Plant Shops are open
Tuesday through Saturday 11 a.m. to 4 p.m.;

Sunday 1 - 4 p.m. Closed on public holidays and
during the deer hunting season. All visitors must
obtain a free permit at the Gifford House for access
to the Arboretum.

MEMBERSHIP

Take out a membership in the Mary Flagler Cary
Arboretum. Benefits include a special member’s rate
for lES courses and excursions, a 10% discount on
purchases from the Gift Shop, six issues of the lES
Newsletter each year, free subscription to Garden
(the beautifully illustrated magazine for the
enterprising and inquisitive gardener), and parking
privileges and free admission to the Enid A. Haupt
Conservatory at The New York Botanical Garden in
the Bronx. Individual membership is $25; family
membership is $35. For information on
memberships, contact Janice Claiborne at
(914) 677-5343.

For more information, call (914) 677-5358 weekdays from 8:30-4:30.

INSTITUTE OF
ECOSYSTEM STUDIES
The New York Botanical Garden
Mary Flagler Cary Arboretum
Box AB, Millbrook, New York 12545

Newsletter

Volume 4, Number 5
September - October 1987

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