His education was interrupted by World War II, when he served in the army from 1942 to 1945; his active service took place in the South Pacific and he attained the rank of staff sergeant.
He was a popular teacher and he established long-term vegetation research projects, providing opportunities for students to conduct field work and analyze change in the natural landscape over time.
His research spanned a variety of ecosystems, from Connecticut's shores and inlands to the islands of the South Pacific to the flora of the Southwest.
He was an authority on vegetation management through controlled burns and herbicide application, which he researched and practiced at the Arboretum.
In 1978 Congress designated the Pine Barrens as the Pinelands National Preserve; this would not have been possible without the scientific knowledge of William Niering.
In February 1980, the United States Department of the Interior awarded Niering the title of Honorary Park Ranger.