Understanding the causes of environmental degradation can lead to more effective forest management. Often, the discussion about the causes of deforestation confuses issues across spatial and temporal scales. Such is the case in the Monarch Butterfly Biosphere Reserve (MBBR) in Mexico where various hypotheses compete to explain the deforestation observed there. This paper analyzes these hypotheses using the analytical approaches developed by the literature on environmental degradation and biodiversity loss. This paper first distinguishes between proximate factors and underlying socioeconomic forces. It then reviews recent deforestation studies to evaluate the relative impact of each proximate factor observed in the MBBR. Illegal logging stands out as the factor with the most empirical support. In contrast, agricultural clearing, while frequently cited as major driver of forest loss, has much less empirical backing. These conclusions update the deforestation diagnosis for this protected area and suggest that more attention should be directed at understanding the illicit timber trade. Copyright © 2008 John Wiley & Sons, Ltd.