This research evaluates the consequences of global environmental change for plant growth, foliar chemistry, herbivore and natural enemy performance, and insect biodiversity. Over the last two decades our primary emphasis has been on enriched carbon dioxide and ozone, with most of our research conducted at the Aspen FACE (Free Air CO2 Enrichment) site in northern Wisconsin. More recently, we explored the effects of climate warming on tree-insect interactions in southern boreal forest, in concert with the DOE-funded B4Warmed project (P. Reich et al., University of Minnesota). We addressed, for example, the consequences of warming for foliar quality, insect performance, and the synchrony of leaf and insect development. Currently we are studying effects of warming and genetic variation in budbreak phenology in aspen, and consequences for forest tent caterpillars.