 Until the completion of his postdoctoral lecture qualification in 1980, he was a research associate at the Wilhelms-University in Münster.From 1980 until 1988, Wittig was professor for botany at the Heinrich Heine University of Düsseldorf and chair of the department for geobotany at the Institute for Plant Physiology.Since 1989, he has been a professor for ecology and geobotany at the Goethe University Frankfurt in Frankfurt am Main.