A group of University officials is researching disease-resistant tree species, searching for a plan to replace the Yard's dwindling American elm tree population.

The committee, which is comprised of botanists, architects and University building officials, hopes to conclude its planning by next spring, said committee member Peter J. Del Tredici, assistant director of living collections at the Arnold Arboretum.

Its main objective, Del Tredici said, will be to develop a long-range plan that will keep the Yard's atmosphere intact.

"The trees are going to continue to die," he said. "Rather than just replace trees one by one, we'd like to have some control over the situation."

According to Del Tredici, every American elm on Harvard's property--about 65 trees in all--will eventually die from Dutch Elm disease. The ailment has forced the University to cut down many trees already, most recently two in front of Holworthy Hall.

Until now, the University has been treating each tree separately, a process which Del Tredici said is very expensive. He said the group would instead like to replace several trees at once.

"Some of those specimens [in the Yard]...are in really pathetic shape," he said. "Let's put in four nice replacement trees as a group where they'll have more space."

The committee is looking for species that will reproduce the Yard's present shadiness. "We've drawn up a list of species that have the same effect--tall bare stems, a high canopy," Del Tredici said. "[It] leaves the view open."

To ensure that a disease cannot decimate all ofthe trees at once, the committee has decided thatno single species should make up more than 20percent of the Yard tree population.

"When one species is susceptible to [adisease], you've got a problem," Del Tredici said."There's going to be much more botanicaldiversity."

American elms currently make up 75 percent ofthe tree population in the Yard.

Liberty Elms

The Elm Research Institute of Harrisville, N.H.has already sold the University 150 Liberty elms,some of which may occupy empty spaces left byfallen American elms, according to Yvonne A.Spalthofs, the institute's assistant director.

According to Spalthofs, the Liberty elms in 80percent resistant to Dutch Elm disease