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Southwest Texas State U. Creates a Digital Map of Trees on Campus

Chronicle of Higher Education (02/14/02)
By Vyacheslav Kandyba


The military uses it to guide munitions. Its signals help drivers navigate with detailed directions. Now Southwest Texas State University is among several colleges that have found a new use for the Global Positioning System -- conducting a tree census.

Many of the campus’s oaks and cypresses are giant and old, and some are historic. The grove includes a cypress planted by Lady Bird Johnson in memory of her husband, Lyndon B. Johnson, who was an alumnus of Southwest Texas State.

“We’ve got a good number of memorial trees, but we don’t know the exact number or where they are because we’ve lost track of the records,” said Bradley M. Smith, director of grounds operations.

“People will call and say, ‘My uncle donated a tree 20 years ago in memory of his wife, and we’d like to come visit it,’” Mr. Smith said. “We scratch our heads because we don’t want to tell them we don’t know where it is.”

Taking a cue from Stephen F. Austin State University and Texas A&M University at College Station, which have undertaken similar projects, Southwest Texas State put to use its own GPS equipment.

The system, operated by the U.S. Air Force, comprises 24 satellites that continually broadcast navigational signals.

A receiver on the ground can use the signals to determine its own location with high precision.

Scholars have used GPS for a variety of scientific purposes, like measuring continental drift.

To count a tree using the system, a student walks up to it, selects the corresponding species on the GPS-unit computer, and is given the tree’s precise geographical coordinates. That information is then sent to a cartographer, who digitally places the tree on an aerial-photo map.

About 2,100 trees at Southwest Texas State, in San Marcos, have been mapped using the process. Several geography students were recruited to help compile the inventory. “It’s normally used in sewer systems, deciding where to place utility poles, so it makes sense to use it for this as well,” said Leah Jane Adams, a recent graduate in geography who helped gather data for the project.

Yvette Gonzales, a sophomore studying geography who also worked on the census, said she had never used GPS but quickly became comfortable with it.

The project is expected to be completed by the end of the spring, about a year after it started.

It is taking that long, Ms. Adams said, because weather conditions sometimes do not allow GPS to function correctly.

When complete, the aerial-photo maps will enable university officials to quickly pinpoint memorial trees as well as allow groundskeepers to better maintain aging trees and monitor those that are at risk.