Depreciative behavior is a significant problem facing natural resource managers. The theft of petrified wood from Petrified Forest National Park is one type of depreciative behavior. Despite numerous anti-theft interventions, approximately 12 tons of wood disappear from the park each year. The focus of this study was to design, implement, and evaluate the effectiveness of interventions to reduce the theft of petrified wood. In addition to gaining a quantitative measure of intervention effectiveness, qualitative interviews were conducted to provide some contextual understanding of wood theft and of designed intervention effectiveness in reducing theft. Tested interventions included a sign, a signed pledge, and a uniformed volunteer. A field experiment revealed a theft rate of 2.1 % under the control condition. All three interventions significantly reduced the theft rate to about 1.4 %. There was no difference in the effectiveness of the three tested interventions. Subjective responses revealed that most theft was not a thoughtless act, but instead occurred because thieves rationalized their particular act of theft as acceptable. The primary rationalization given by thieves was that their piece of stolen wood was so small that taking it would not hurt anything. It appeared as though anti-theft messages were received by most of those interviewed, but that thieves only applied these messages to the larger pieces of wood. In addition, most thieves did not view taking a little chip as stealing. Interviews suggested visitors attended to the following aspects of the interventions: the desired behavior itself, the negative consequences of theft behavior, the visitors' responsibility for those consequences, the sanctions involved for the behavior, and visitors giving their word not to steal any wood from the park. / Ph. D.