Woods 1993 (IMAGE) University of Wisconsin-Madison Caption A Southern Wisconsin woods being strangled by buckthorn, a tree that was sold in nurseries and started to invade the region over the past half-century. As buckthorn excludes all other vegetation, this site that was formerly dominated by oak shows some of the ways that human activity has changed the relationship among species, as described by UW-Madison botany professor Donald Waller and co-authors in a new study in the journal Nature. Credit David J Tenenbaum, University of Wisconsin-Madison Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.