Unfortunately, this link expired and the video is difficult to embed, so here is a link to the National Geographic film about the ongoing experiments studying the effects of CO2 and ozone on trees.
It seems very premature to say things like elevated CO2 is good for plants - like an "all-you-can-eat buffet." What has that sort of overindulgent diet done for the health of the average American?
Since the trees and plants evolved to live in the atmosphere with pre-industrial levels of CO2, it strikes me as simple logic that higher levels will ultimately damage vegetation. Nobody knows that leaves that are slightly larger and grow slightly faster will contain the same nutrient levels, or whether trees will produce nuts and fruit with sufficient minerals and vitamins required by the animals that feed on them, for instance.
In any event the looming crisis from ozone damage (and quite possibly worse effects from burning ethanol, which as far as I can tell aren't included in this study, nor for that matter is the serious effect of acid rain depletion of essential soil nutrients) is much more urgent than the question of CO2 effects.
A most important finding is the subsequent vulnerability of trees exposed to ozone to secondary insect and disease, the "sharks smelling the blood." It's time for those researching the pine bark beetle, sudden oak death ostensibly from a fungus, sudden aspen decline, etc., to make the link between ozone exposure and compromised immune systems.
Let's hope these scientists will have the courage to make a correlation between their controlled studies in Wisconsin and what is happening in the dangerous uncontrolled experiments going on in our woods, parks, back yards, and farms. Our government agencies and elected officials must become aware that we are threatening not just trees but our food supply with our reckless polluting through toxic greenhouse gas emissions.
As far as I'm concerned, this evidence is conclusive enough to be the basis for a lawsuit against big, lying corporations.