|
Frontiers
Swingin' in the Rain Life in Forest Treetops
December 1997
How many people would be delighted if they
had an ant named after them, and by their intended at that?
If they're biologist Nalini Nadkarni of Evergreen State College in Olympia,
Washington, they would.
Nadkarni, whose research is funded by NSF's Biological Directorate's
Divisions of Environmental Biology and Biological Infrastructure, met
her husband-to-be while playing Jane to his Tarzan: both study the tippy-tippy-tops
of trees, called tree canopies. Jack Longino, now Nadkarni's husband,
is an entomologist who fell in love when Nadkarni taught him to climb
trees so he could study ants. Her reward? A species of tree canopy ant
named after her: Procryptocerus nalini.
Treetop Explorations
Until recently, the forest canopy was considered one of the last frontiers
of natural science-so close, yet impossible to reach unless your scientific
prowess happened to include rope-swinging. But now researchers ascend
to the treetops in such T.rex-tall contrivances as canopy cranes, an extension
of the telephone repairperson's cherry-picker bucket device. As chair
of the scientific committee for the Wind River Canopy Crane, one such
crane currently in use in the Pacific Northwest, Nadkarni helps decide
which experiments should be done from the crane. But, she says, she still
enjoys tree-climbing inch-by-wormlike-inch.
"Another continent of life remains to be discovered, not upon the earth,
but one to two hundred feet above it," wrote naturalist and explorer William
Beebe almost 80 years ago. "There awaits a rich harvest for the naturalist
who overcomes the obstacles-gravitation, ants, thorns, rotten trunks-and
mounts to the summits."
Nalini Nadkarni has certainly overcome those obstacles. She's now president
of a group of scientists known as the International Canopy Network (ICAN).
ICAN, created in 1994, facilitates communication among individuals and
institutions concerned with research, education and conservation of tree
crowns and forest canopies.
The tree canopy is defined by ecologists as the aggregate, including
air space, of every tree crown in a forest: foliage, twigs, fine branches
and epiphytes-plants like bromeliads that grow on other plants. Until
quite recently, says Nadkarni, the canopy had not been studied in situ.
The treetops remained an unexplored world.
"Then in the early 1970s, a small group of scientists penetrated the
canopy and began documenting the organisms and interactions of the treetop
world," explains Nadkarni. "Their findings fundamentally altered the notion
of what a forest is."
Getting Up There
Initial work on tree canopies was focused almost exclusively on access.
Researchers first modified caving and mountain-climbing techniques for
use in trees to study natural cycles in old-growth Douglas fir forests.
It's no longer necessary to don climbing boots to reach the tree canopy;
cranes, cables and hot-air balloons extend a biologist's reach well into
the treetops.
But when Nadkarni started 20 years ago, things were more free-swinging. "I
can still recall my first day in a tropical rainforest canopy, where low-hanging
clouds and lush trees rarely allow the sun to penetrate. Every surface
of every branch and trunk was covered with mosses and flowering plants,
but my eyes were drawn to the treetops. I wanted to climb up, out of the
damp stillness of the forest floor."
A month later, in a Costa Rican forest, Nadkarni got her wish. With a
powerful crossbow, she launched a weighted fishing line over a branch
some 125 feet up. Then, with techniques similar to those used by rock-climbers,
Nadkarni began to scale her first tropical rainforest tree. "I climbed
that tree much like an inchworm." Once in the canopy, Nadkarni had entered
another world, one with its own weather, smells, sounds and life. Far
below were the dampness and gloom of the forest. "Around me were wheeling
birds, brightly colored insects and sky. From my perch I could see for
miles around."
Questions bloomed in Nadkarni's mind: How do plants survive in this environment?
Without root connections to the earth, where do their nutrients and water
come from? What role do the organisms of the canopy play in the larger
environment of the forest? No textbook had ever addressed such questions. "I
knew," says Nadkarni, "that I'd be back, and very soon."
Canopy Life
Tree-climbing, she says, felt like too much fun to be real science. Nonetheless,
Nadkarni embarked on a study of epiphytes in rainforest canopies. Although
epiphytes grow on other plants, they don't rely on their hosts for water
or nutrients. Epiphytes merely perch on trees; even if pulled off their
hosts, they will often survive. If a canopy epiphyte falls to the forest
floor, however, it will eventually die, likely from lack of sunlight.
Nadkarni discovered that in temperate rainforests the amount of plant
material embodied in epiphytes is four times greater than that of their
host trees. In tropical cloud forests, the epiphyte nutrients make up
about half the nutrients of the tree foliage. About 80 percent of the
organic material that makes up the thick mats in the tree crowns of the
rainforest is dead; it becomes "crown humus," or true soil, formed when
epiphytes die and decompose in place. That organic matter, supports self-contained
mini-ecosystems high above the forest floor, "complete with arboreal earthworms,
beetles, ants, plants and pollinating birds. But because that soil is
nearly 10 times as acidic as the soil on the ground, much of the life
it supports is quite different from the life on the forest floor." Nadkarni
carried out her dissertation research doing a comparative study of canopy
plant communities in a temperate rainforest (Olympic Peninsula, Wash.)
and a tropical cloud forest (Monteverde, Costa Rica).
As interest in forest canopies grew over the next 10 or more years, means
of access also developed. Antenna tower systems were erected to study
meteorology from the forest floor to above the canopy. And now the use
of large construction cranes has enabled biologists to collect data from
nearly any treetop location while sitting comfortably in a gondola chair. "The
old slingshot method of canopy access has all but been replaced," says
Nadkarni, with some regret.
With data flowing in on tropical, temperate and boreal forest canopies,
now the dilemma of tree canopy research, Nadkarni contends, is one of
information management. "Data from the canopy is valuable to geographers
and land-use managers, and information from those fields can in turn aid
canopy ecologists. But such reciprocal use of information demands that
one think in advance about how the data should be organized, to ensure
that it will be usable."
To address that very issue, Nadkarni and scientist Geoffrey Parker of
the Smithsonian Environmental Research Center in Edgewater, Maryland,
received a planning grant to bring together forest canopy researchers
and scientists from other fields. They are developing methods of dealing
with what Nadkarni calls three-dimensional data. Canopy research and its
results are fragmented, she says, and in dire need of standardization. "But
shifting research activities from forest to computer may not come easily
to those accustomed to long days hanging hundreds of feet above the earth."
And Structure
Although Nalini Nadkarni speaks with vigor of the need for scientists
to commingle their data and find a common voice, one has the feeling that
her true passion lies outside her Olympia office windows, among the silver
firs, white pines, cedars and hemlocks of NSF's H. J. Andrews Long-Term
Ecological Research (LTER) site, one of 18 such NSF sites in North America
and Antarctica. Here Nadkarni is involved in a project to collect rainfall
to develop a picture of canopy structure and how the amount of rainfall
affects it.
Nadkarni's current project involves collecting forest function data by
putting rainfall gauges beneath the canopy on the forest floor. Other
researchers are collecting information on the trees above and around her,
documenting characteristics such as tree crown projection area, canopy
volume, and leaf area index. She hopes to use this data to understand,
and eventually predict, the amount of variability of rainfall hitting
the ground. "This project presents not only the normal joys and challenges
of canopy field research," she says, "but also the obstacles and triumphs
that come with collaborating with researchers from completely different
fields. Here we have hard-core rope-ascenders plunking away at computer
terminals, and computer nerds riding high on the crane gondola-it's an
unlikely but terrific way to push forward one frontier of science."
These days, says Nadkarni, to ask good questions about the forest canopy,
you have to see beyond your own field of science and think like a bird,
an ant, a raindrop or a strand of moss, as all are interconnected. From
her background as a dancer (she chose a career in biology over dance,
but just barely), she's learned to see tree canopies and research on them
as the music of the trees: wind rustling through pine cones and mosses,
which, in an ideal world, would mingle with harmonies on the ground of
canopy ecologists singing in one key, making music on a set of instruments
all can interchangeably play.
|
