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Seeing Forests Through the
Trees
By Gabrielle J. Corcoran
and A. Mark Dalessandro
James
B. McGraw, the Eberly Family Professor of Biology at WVU, was conducting
research on plant species in the Appalachian Mountains when he decided there
had to be a better way. McGraw, interested in tracking individual trees over
time in order to predict the future of forests, wanted to increase the number
of trees he could examine.
Dr. Timothy Warner and Dr. James McGraw
In
the past, a plant biologist like McGraw or a forester would need to walk
through a forest, using tape measures and other low-tech tools to collect
information. The scientist collected samples from a limited area, then drew
conclusions about the entire forest based on the sample.
Although still very useful, these methods allow only for examination of trees
by the hundreds. McGraw wanted to examine millions.
"In our profession, population biology, we tend to work with a few
hundred trees or a thousand trees because that is all we can do from the
ground," McGraw says. "The real question is: What are a million
trees doing? You can't extrapolate to a very large area from 500 trees."
Remote sensing, an often highly technical scientific approach to collecting
and interpreting specific information without actual contact with the object
being examined, has become a widely used method for obtaining information
about the earth's surface. Images of the earth are taken from satellites or
by using other technologies. Then, a computer processes the data and isolates
the desired information.
Using remote sensing to examine trees enables the researcher to assess the
resources of an entire forest and collect information about varieties, sizes,
and total numbers of species in the forest.
Researchers in many different fields and industries use remote sensing of
data to obtain information they were not able to acquire in the past. The
Robert Mondavi Winery in California's Napa Valley, for example, is
collaborating with NASA to use digital remote sensing to help winemakers
harvest their grapes at the peak of ripeness.
McGraw thought he could use a similar approach to increase his sample from
hundreds of trees to millions, and as a result more accurately draw
conclusions about environmental change.
"Applying remote sensing to my research would be particularly helpful
when you have environmental problems like global climate change and you
expect the changes to be pretty subtle. If you predict only a one percent
change in mortality, detecting that on 500 trees is very difficult because
you only expect five trees to die," explains McGraw. "But if you
look at five million trees, it becomes much easier to detect."
Applications of this technology include the detection of rare or endangered
species, which can lead to their conservation and restoration. Identifying
the presence of pests before a fatal attack is another valuable function.
Computer programs capable of analyzing an image of a forest and singling out
particular characteristics about a species in that image have been under
development for more than 20 years. But these programs are designed for
northern forests where the species are primarily coniferous and contain fewer
varieties. Forests in the southern Appalachians, such as those under
observation by McGraw, contain many more varieties of coniferous and
deciduous tree species, making differentiation between individual species
much more difficult.
This fact did not deter McGraw. If a program capable of analyzing an image of
more complex forests did not exist, he and his fellow scientists would create
one.
Unaware of the complexity of developing such a program, McGraw approached
Timothy Warner, a WVU associate professor of geology and geography, for help.
Warner, a native of Zimbabwe, is an expert in the spatial analysis of
remotely sensed data. He told McGraw the project was not viable.
He was wrong.
"I had only worked on much coarser scales where you can't differentiate
between trees, and therefore I was biased," says Warner. "McGraw
was limited in his knowledge of remote sensing, but not in his
thinking."
Despite his doubts, Warner did not completely close his mind to the
challenge. He assigned Thomas Key, a geography graduate student, to
investigate the project further. Key's research indicated that there were
ways to identify individual species. So, Warner and McGraw decided to seek
funding to develop the required technology.
NSF-EPSCoR (National Science Foundation Experimental Program to Stimulate
Competitive Research), a program to enhance federal funding to states in
need, approved their proposal and provided them with $50,000 to begin work on
the project. Because the project was viewed as risky, they would need to make
substantial progress before seeking further funding.
Now, after five years of research, including a three-year, $332,000 grant
from the NSF, the WVU project has made breakthrough advances in remote
sensing.
"We are taking a new perspective on plant population biology,"
McGraw says. "Instead of walking through the forest, we are looking at a
complex forest from above and collecting data that was previously only
possible from the ground."
Writing a computer program capable of identifying individual species located
in forests as diverse as those of the southern Appalachians might have been
impossible without the help of Tomas Brandtberg, who earned his doctorate at
the Swedish University for Agricultural Sciences in Uppsala.
Brandtberg had just completed his dissertation on high-spatial resolution
remote sensing and was looking for work. The timing could not have been
better for Warner and McGraw, who were searching for someone with the
expertise Brandtberg displayed in his dissertation, which received an award
from the Royal Society of Sciences in Uppsala. In addition, Brandtberg's
extensive knowledge of forestry enabled him to appreciate the difficulties he
would face in developing software to analyze a complex forest.
Warner hired Brandtberg as a post-doctoral research associate and research
assistant professor of geography. "We are extremely fortunate to have
him here because he is on the cutting-edge of high resolution remote sensing
research," McGraw says. "His work is some of the best in the
world."
With Brandtberg hard at work writing computer algorithms, Warner and McGraw
have developed methods to identify individual species once the computer
program makes the distinction between the different plants. One method, based
on tree phrenology—the timing of leafing out and the coloration of tree
foliage—can be used to recognize specific species during a particular time of
year.
"Dr. Brandtberg is making considerable progress delineating the edges of
individual trees and then using these color patterns to distinguish
species," McGraw says.
 
Aerial view of a plot in Cooper’s Rock, WV, in late fall, and the same
plot with mapped canopy trees.
Studying
the leafing-out of trees has proven to be effective, but it assesses only the
forest's top layer. So, a LIDAR (light detection and ranging) instrument that
detects plants beneath the forest's canopy has been incorporated in the
investigation. McGraw explains that, by using signals that travel through the
leaves, LIDAR can detect both the location and amount of vegetation.
"The LIDAR method is very significant because it will also construct the
three-dimensional shape and height of the tree," Warner explains.
"It can do this by measuring the tree at several points in order to
reconstruct its actual shape and potentially reveal what lies beneath."
Aerotec,
a remote sensing company that specializes in LIDAR and digital image surveys,
provided the data used for this research free of charge through a procedure
that typically costs about $50,000. Aerotec, which was experiencing similar
struggles in devising methods to identify particular trees from LIDAR data,
sees potential profits in a commercial spin-off that could come from its
collaboration with the WVU researchers.
Forestry companies, for example, may be able to use the technology to
inventory their resources and plan selective cutting to maximize long-term
forest health. McGraw explains that land managers will be able to classify
forest communities in greater detail than previously possible, know where
rare species are found, assess changes in forest composition, and use the
detailed canopy maps to guide management plans.
"The hope is that we both benefit," Warner says. "For us,
access to data from a state-of-the-art system, acquired by professionals who
have tremendous expertise in capturing this data, is invaluable. For Aerotec,
there is the possibility that our work will improve an aspect of their work
and open new markets in forest mapping."
McGraw and Warner are excited about the potential applications of their work,
including the possible restoration of the American chestnut tree. This
species, once one of the most valuable of the eastern deciduous trees, was
eradicated by the chestnut blight in the early part of the 20th century.
However, a few adult trees may have survived, and could potentially be
located through remote sensing.
Hickory trees, another valuable species found in the Appalachian forests, are
also declining in numbers, but only in particular regions. By examining
environmental factors of the different regions, researchers could possibly
identify which factors are causing the decline of this species.
Rick Landenberger, a post-doctoral research associate and a research
assistant professor of biology, has been working on the tree delineation
project and another project McGraw and Warner began last fall involving
censusing natural populations of silversword in Hawaii's Haleakala Crater.
Remote sensing, in conjunction with on-the-ground monitoring of this unique,
long-lived plant species, may allow for a more accurate and complete census
of the federally protected silverswords. Landenberger has coordinated the
data acquisition and processing on the silversword project, which McGraw
plans to continue working on during a sabbatical this fall.
Haleakala Crater, Haleakala National Park, Maui, Hawaii
M.
Duane Nellis, dean of WVU's Eberly College of Arts and Sciences and a
professor of geography, has also been collaborating with Warner and McGraw on
vegetation inventorying and monitoring projects.
"We are especially pleased to be working with Duane," Warner says.
"He has an incredible reputation in the discipline of remote sensing,
and brings a great deal of knowledge and expertise to the project."
Although Warner and McGraw have begun to employ their research in a number of
projects, their work is nowhere near complete. They are uncertain if each
species has a unique color signature, which will be necessary for the
leafing-out method to be effective. They have begun examining the
possibilities of using other attributes, such as branching patterns, to
identify species. Continuing to refine the technologies used to locate
individual trees in the images and identifying them by species is their
primary research focus for the next several years.
"These problems are not completely solved at this point," says
McGraw. "Another area in development is taking images in different years
and determining whether we can pick out the death and birth of canopy trees.
This kind of information could lead to predictive models of forest
change."
"There are all these different aspects that need to be examined
here," Warner says. "There is the issue of the rare and endangered
species, the examination of subtle changes in population of common species,
the LIDAR and structuring the three-dimensional shapes of the trees, as well
as the color patterning. Even though we have a very focused number of
questions that we are working on at this moment, it really is a huge research
agenda."
WVU
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