Ask Dartmouth has an article on campus trees, a popular topic; this one mentions that the elm in front of Wilson Hall (the tall one on the small grass oval surrounded by the paved path?) had to be removed. The OPDC also had a notice about this:

6/30/08 – IMPORTANT NOTICE:

The elm tree in front of Wilson on East Wheelock Street was diagnosed with Dutch Elm Disease. In order to prevent the spread of the disease to other adjacent elms on campus and in the town, the tree will be removed today, Monday June 30th, by the Town of Hanover. In some cases,trees can be saved with treatment and removal of the affected areas, but in this case the disease was too widespread as determined by the College and Town staff working together.