By the 1930s, Leopold was the nation's foremost expert on wildlife management. He advocated the scientific management of wildlife habitats by both public and private landholders rather than a reliance on game refuges, hunting laws, and other methods intended to protect specific species of desired game. In his 1933 book "Game Management", Leopold defined the science of wildlife management as "the art of making land produce sustained annual crops of wild game for recreational use." But, as Curt Meine has pointed out, he also considered it to be a technique for restoring and maintaining diversity in the environment.