My main research interests are in forest ecology and vegetation dynamics in relation to natural and anthropogenic disturbances, especially as related to climate variability. I use tree rings to date past disturbance events such as fire and insect outbreaks. For more than 25 years I have been investigating how disturbances such as fire, blow down and bark beetle outbreaks interact in the forested landscapes of the Colorado Rocky Mountains. Since the mid-1970s in the southern Andes of Chile and Argentina I have been investigating the effects of disturbances such as mass movements, blow down, fires, and introduced animals on forest dynamics, and increasingly under the effects of climate warming. Both my Colorado and southern Andean work are supported mainly by the National Science Foundation.