woodlands on the UC Santa Cruz campus could alter U.S. trade
policies. Madolyn Bowman Rogers hikes in to find
out how. Illustrated by Jon
Gregory Gilbert doesnt look
like a classic adventurer. A soft-spoken, slender man with glasses
and a neatly trimmed beard, he would look more at home in a lab.
But on this chilly January morning hes striding through a sodden
forest in boots and a black leather jacket, wielding a trowel and
a 5-gallon pail. I struggle to keep up, jumping over rivulets and
clambering over tangles of fallen branches crusted with gray-green
lichens. Mud sucks at my boots, and an incautious step into a
puddle sends water squelching through my toes.
Gilbert, an ecologist at UC Santa Cruz, is oblivious
to the soaking ground. Hes gazing through the jumbled maze of
Douglas fir, oak, and thickets in search of one particular tree.
Dappled sunlight dances over a patchwork world of green and brown,
gleaming on great oak trunks cloaked in emerald moss like wet velvet.
The only sounds are a faint twitter of birdsong and the rush of
cars from a distant road. I stare where Gilbert does, but I know
were not seeing the same things.
this California forest is no maze, but a laboratory where his team
knows the location of every last tree and shrub down to a few
centimeters. Every woody plant for acres wears an aluminum ID tag,
and a grid of yellow flags spots the forest floor. Its part of the
powerful new way modern ecologists like Gilbert are studying natural
ecosytems, gathering data in exhaustive detail.
Gilbert finds his target, a Shreve oak tree. He
kneels beside its trunk, scrapes leaf litter aside with his trowel,
and ladles thick black muck into a labeled baggie. His fingers are
dark with dirt, but hes got his prize. The soil is a treasure trove
of microorganisms, which Gilbert will take back to the lab for
Gilbert studies disease ecology,
or the way natural plant diseases shape forests and other ecosystems.
His discipline is only two decades old, and wide open with opportunities
for an enterprising pioneer. Just last year Gilbert completed a
ground-breaking and massive study in the jungles of Panama suggesting
that individual plant diseases can infect a broader range of species
than was thought. Now hes repeating the study in the temperate
coastal forests of California. If his results hold true here, it
will mean U.S. forests are more vulnerable to an invasion by foreign
diseases than was hoped. His results could alter U.S. Department of Agriculture
plant quarantine rules and have far-reaching consequences on
global trade and plant imports.
A new way
to study forests
Scientists have studied
plant disease for more than 150 years, but they paid attention
mostly to its effects on agriculture. Not until the 1980s did they
begin to consider the role that plant disease plays in shaping
ecosystems. They found that disease in forests is not a destructive
force, but a natural check and balance that prevents any one species
from dominating the woods. Diseases actually may help maintain the
dizzying diversity of tropical rain forests. Although plant diseases,
or pathogens, come in many forms, the most numerous, diverse, and
powerful ones by far are fungi.
fell in love with the weird world of fungi as an undergraduate at
the College of
Environmental Science and Forestry in Syracuse, New York. Each
person in his mycology lab was given a glass bowl full of horse
dung and told to identify the fungus that grew from it. Dung can
sprout Pilobolus fungi that look like little eyes on stalks,
or the twisting white tubes of Coprinus, but Gilberts bowl
grew a fuzz he couldnt identify. His professor was just as stumped.
It took a fungus expert to explain it: Gilbert had discovered a new
I thought that was a really cool
thing as an undergraduate to take a pile of horse dung and discover
something nobody had ever seen before, Gilbert says.
His fascination with fungi led him to study plant
pathology as a graduate student, but his interest was in how fungi
affected natural communities. When he graduated in 1991, only five
or six researchers in the world studied plant diseases in natural
ecosystems. Gilbert traveled to the Panama rain forest to collaborate
with a leading plant ecologist, Stephen Hubbell. The event
would shape the rest of Gilberts career.
then a professor at Princeton University, and his colleague Robin
Foster, a scientist at the Smithsonian Tropical Research Institute, had
recently set up the first large mapped research plot in the world.
The plot spanned 50 hectaresabout 124 acresin the rain forest of
Barro Colorado Island, a vibrant green jewel in Gatun Lake along
the Panama Canal waterway. Hubbells team had slaved for two years
to tag, identify, and map every tree and shrub in the plotabout
200,000 plants representing hundreds of species.
mapped plot allows ecologists to collect rigorous data. Scientists
examine the spatial distributions of plants to look for patterns,
and they track individual trees for years to see whether they thrive
or die. Chaotic forest is transformed into laboratory. When Hubbell
and Foster did their first plot in 1981, it revolutionized thinking
about tropical forests, Gilbert says.
in the jungle
Gilbert continues to work
on mapped plots in Panama, spending two to three months a year
there, usually in the summer. In a side project, hes helped a local
Indian population deal with a mysterious palm disease (see sidebar). He has a house in Gamboa,
a former canal town that has become an enclave of scientists. The
town has no stores or gas stations, and only one restaurant. Gamboa,
Gilbert says, is the end of the road. Theres nothing beyond but
forest. Gilbert and his team bicycle out a mud road every morning
into the hot, muggy jungle, where they decipher the arcane rules
of pathogen and plant interactions.
pathogens prey on specific plants. No pathogen can eat everything,
Gilbert says, but some have broader host ranges than others. In
2006, Gilbert and his team decided to find out just how broad a
range pathogens could have. Everybody knows that more closely
related plants are more likely to have a common plant pathogen than
two plants that are not closely related, he says. But until we
published a paper last March, nobody had ever actually measured
this or done the testing to say, How different do the plants have
To answer this, Gilberts team gathered
53 fungal species that grow on leaves in the Panama forest. The
fungi normally spread by airborne spores. The scientists clamped
small cultures of each fungus on leaves of other tree species that
grow in the same area. Each fungus was tested on about 15 tree or
shrub species, for almost 1000 total pairings of plant and fungus.
After a week, the team returned and plucked the infected leaves.
Taking them back to the lab, they looked for signs that the new
trees were succumbing to infection.
results surprised them, Gilbert says. The assumption in the field
has always been that a pathogen might attack plants in the same genus or family
as its normal host, but nothing more distantly related. In other
words, a pathogen that feeds on one species of palm would attack
only other types of palms. Some quarantine policies in the U.S.
are based on this assumption.
Gilberts work, published March 2007 in the Proceedings
of the National Academy of Sciences, confirmed that closely
related plant species are most likely to share pathogens. Yet it
also showed that fungal pathogens could attack a much broader range
of plants than anyone had guessed. Even among plants in different
orderstwo levels of classification beyond plants in the same
familyfully one-quarter of them could share pathogens. That would
be like a palm sharing a disease with a pea plant, Gilbert saystwo
species as distantly related as an elephant and a mouse. Thats
something we were not expecting at all.
data sparked great interest among his colleagues. Keith Clay at Indiana University,
one of the founders of the field of disease ecology, calls Gilberts
paper a really massive effort with important practical implications
for quarantine policy. The kind of exhaustive, detailed study they
did here has never been done before. I give him a very high rating
for taking on such a large project and providing definitive data
supporting what traditionally has just been assumed, Clay says.
|Slideshow: Author Madolyn Rogers assembles images
from the team's field research in Panama. (Click
image to launch show.) |
Matteo Garbelotto, a
mycologist at UC Berkeley, says of Gilbert, His biggest contribution
to the field is to provide these large data sets that prove or
disprove scientific theories. The proven theory of plant-pathogen
interactions will allow scientists to build better predictive models
of disease susceptibility, Garbelotto says. Invasive organisms are
a big issue right now. So to have this tool so solidly laid out
for us in the paper is quite important.
the northern forest
Panama experiment was limited to tropical forests and tropical
diseases. To find out if the results reflect a general rule in
biology, Gilberts lab is repeating the experiment in temperate
coastal forest on the UC Santa Cruz campus. In late 2006 the team
laid out a six-hectare plotabout the size
of 12 football fieldsin the northern hills of the 2000-acre campus.
Over the next year, teams of undergraduate interns, graduate students,
and technicians mapped and identified every tree and shrub on the
plot, creating only the worlds third mapped plot of this size in
Project coordinator Beth
Howard describes how every morning the team would assemble at the
lab, grab their gear and venture into the woods. Half an hours
hike up a steep fire road, in the green depths of the forest, they
would begin their days work.
To turn wild
woods into precision laboratory, the team first mapped out a grid,
dividing the plot into 150 squares each 20 meters by 20 meters,
then dividing each of these into four squares 10 meters on a side.
Every line on the grid had to be straight and accurate to the
centimeter. The team used a compass to measure direction, but
instead of measuring distance with an old-fashioned tape measure,
they used a hypsometer, a fist-sized black box that looks like a
tiny video camera. It emits a laser beam that travels to a transponder
unit several meters away, which chirps and sends back a signal.
The signals transit time reveals the distance. The students marked
the grid by driving small yellow flags into the forest floor.
Once the grid was in, the team went back to
each small square to map every woody plant in it, starting
systematically in the southwest corner of the square and circling
clockwise around it. Every tree and shrub was identified, measured
and located on the grid, again using the hypsometer. The 8,175
woody plants on the plot included only 31 species, less than one-tenth
the diversity of the Panama rain forest.
of the most common plants on the plot is poison oak, and the team
had to wade straight into it to measure and map it. Although they
wore protective suits, it wasnt enough to prevent several nasty
cases of the rash. Probably everybody had it at a low level the
whole time they worked on the project, Howard says. The team also
worked through pouring rain, cold, and sweltering heat. Yet Howard
and graduate student Barbara Ayala say the camaraderie of the team
more than made up for these discomforts.
youre in the poison oak, you can complain together, and when it
rains on you, you can huddle together under a tree and eat trail
mix. You get past any barriers with each other pretty quickly,
Ayala and Howard also speak
with passion about gaining a deeper understanding of the forest.
Its like when I first started using glasses, Ayala says of her new
ability to see details. In the beginning the forest is just green.
Its all blurry and you have no idea what is what. And then suddenly
you can see the layers of vegetation and the different species and
For todays ecologists,
this old-fashioned connection to the land is now married to the
most modern techniques of biology.
A new way
to regulate plants?
Gilberts lab rooms are
a clutter of machines, microscopes, and sterile plastics, like any
modern microbiology lab. Here the team is seeking to repeat Gilberts
results from Panama. They place infected leaves from the UC Santa
Cruz plot into Petri dishes to cultivate the fungi inside them.
Rows of tiny dishes line a cart, each one covered in a fungal fuzz
of slate-blue, black, or tan. The fungi will be identified not by
microscope as in the old days, but by DNA fingerprinting. The team
will then take the native fungi back to the field and spread them
on new tree leaves to track which species succumb to infection.
Gilberts team will collect the data within the
next few months, and by fall 2008 will have the answer he seeks.
Was the broad infectiousness of fungal diseases unique to the rain
forest, or a general rule that applies to U.S. forests as well?
The U.S. tries to seal its borders to any plant
that might harbor a pest capable of attacking native plants or
crops. The regulations on what can come into the country are based
on data from other countries that show damage to particular species
of plants, says Larry Hawkins, California spokesman for the USDAs
Animal and Plant
Health Inspection Service. The agency frequently updates its
regulations as it receives new data, Hawkins says. But if the data
dont exist, mistakes can be made, with devastating consequences.
For instance, Sudden Oak Death invaded
California about 12 years ago. It almost certainly escaped from a
foreign plant in a nursery, ecologists believe. This aggressive
disease already has infected billions of trees and threatens the
survival of oaks over much of the state. It probably escaped
quarantine because it can feed on more than 120 different plant
species, making it even more voracious than the multipurpose fungi
Gilbert documented in Panama.
work shows that distantly related temperate plants can share diseases
too, the result might be both worrisome and empowering to the USDA.
Although the risk of invasive diseases might be higher than was
thought, Gilbert thinks ecologists will have enough data within two
years to create a predictive model of which pathogens will attack
which plants, providing an important tool to help prevent another
crisis like Sudden Oak Death.
envisions a web-based program that would examine the known pathogens
of any plant being considered for importation and provide a short
list of native plants that might be affected by the diseases. Those
plants could then be tested for susceptibility. I dont see it as
a way to stop movement of plant material. Its more a way of making
those decisions on an informed basis, which are currently made based
on rough guesses, he says.
thinks his findings may change the way disease ecologists study
plant and pathogen interactions. This is not what we thought it
was five years ago or two years ago, Gilbert says. A lot of people
are excited about being able to use this quantitative model as a
way of shaping ecological research. Yet as Gilbert and his team
have shown, no matter how modern the research methods get, theres
still no substitute for getting out in the field, wading through
the poison oak, and getting dirt on your hands.
Invisible Killer Sweeps In an era of global trade, nations struggle to
fence out new diseases. They know epidemics come mainly when
pathogens invade new territory, as dramatically demonstrated by a
disease ravaging the coconut palms of Panama. It appeared without
warning in 1994, sweeping through groves of swaying palms. One by
one the great plants succumbed, their leaves withering, leaving
behind dead trunks like headless sentinels.
The effect was alarming to the Kuna Indians, who dwell on the islands and coast
of Panama and still follow the old ways. Coconuts are the basis
of the Indians diet and economy. Their culture could not survive
But there was little response
to the Kunas plight until a young plant pathologist working at the
Smithsonian Tropical Research Institute in Panama, Gregory Gilbert,
volunteered to study the epidemic on his own time in 1998. Gilbert
and his colleagueand future wifeIngrid Parker met with tribal chiefs and explained
the work they wanted to do. Eventually the Kuna helped them map
the spread of the disease and seek clues to its origin.
The disease, called Porroca by the Kuna, had
migrated from Colombia. Its cause baffled the researchers. It
took four years and the help of another disease specialist to finally
pinpoint the organism. Porroca was caused by a phytoplasmaa
tiny, wall-less bacteria that can only live inside the body of its
host. Since it cant be grown in a dish, scientists can only identify
the insidious killer by analyzing its DNA.
after the microbe was known, Gilbert and Parker had no easy answers.
Phytoplasmas are spread by tiny insects that fly from palm to palm.
Among the thousands of insects in Panama, the hunt for the culprit
could be long. Efforts to contain the disease by cutting down
infected palms met with only mixed success.
showed that the easy solutions wont work, Gilbert says.
Fortunately for the Kuna, the spread of Porroca
seemed to peak in 2000. A few areas have since recovered, following
the death of infected palms. Gilbert and Parker continue to study
Porroca, seeking to prevent future outbreaks. But for now, fortune
has spared the Kunas culture.
Madolyn Bowman Rogers
B.S. (Spanish) University of
B.S. (biology) University of South Florida
Ph.D. (developmental biology) Stanford University
Joint Genome Institute news office (Walnut Creek, CA)
As a child I idolized Mr. Spock, the brilliant
science officer who sought out endlessly fascinating new worlds.
He ignited my imagination with the desire to discover. I entered
graduate school with dreams of solving the brain's mysteries and
finding cures for devastating diseases. But after a few years,
these bold visions narrowed to a microscope field crammed with
colored cells. I endured countless sunny Saturdays entombed in the
dark, tallying tens of thousands of cells until my mind went numb
and my fires died.
My passion rekindled
only when I looked up from my microscope to be dazzled again by the
vast expanse of science. I realized I loved the variety and adventure
of the field, not its narrow focus. When I became a science writer,
I could at last explore the infinite universe.
. . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . .
. . . . . .
Jon Wagner (08)
Earlham College, Indiana, 2004
Internship: Sonora Desert
Museum, Tucson, AZ.
up in southeastern Kentucky, where I spent much of my time drawing
pictures, playing outside, and watching cartoons. I liked to draw
more than I like to read or write, so I used art to tell stories
about the characters I saw and imagined. There were comics about
the family of bullfrogs that lived in the creek beside my house and
a new series of ninja turtles that included a samurai flying squirrel
and a Rambo snapping turtle. My style has changed over the years,
but I continue to make art about the lives of natural characters.
My goal is to accurately describe plants and animals in a way that
is engaging and thought provoking for a large audience. This summer,
I'm doing an internship at the Sonora Desert Museum in Tucson,
Arizona. For more about my work, visit http://www.jonstreehouse.com