Arnis graduated from the VSF in 1960, and with a BSc from the University of Melbourne in 1963.   

He worked with the FCV in forest assessment, in the Bright Forest District as Assistant District Forester,  and then in Fire Research at Daylesford and Creswick, before joining the Ministry for Conservation in 1974 to work in Environment Assessment. From 1977 to 1991 he worked for the National Parks Service, overseeing the research program. He then worked on planning projects as an environmental consultant, and as the Director of the Trees for Profit Research Centre with Melbourne University for several years, before fully retiring in 2003.