Jim Morrison said Dunn belonged to a gang of "trail blazers and mavericks" who helped to found the profession in Northern Ireland in the early 1970s.
With colleagues Robert Carson, Peter Deihl and Brian Woods, Dunn helped define public-sector design with such landmarks as the new town of Craigavon.
When Dunn began, his job was virtually impossible, said Morrison, in an "atmosphere resistant or mystified by it (landscape design) and in a country torn apart by civil and political chaos".
Morrison continued: "Jack sought to lead by example, not by bluster or rhetoric." Dunn was married to Peggy and had a son and two daughters.