From time to time people we meet on the trails tell us that the amount of poison ivy they run across seems to be greater than they remember. Some research by Lewis Ziska, plant physiologist for the Department of Agriculture sheds a little light on the issue.
By comparing the growth of poison ivy in an atmosphere containing a carbon dioxide level equivalent to that of 1950 (300 parts per million) with that from the current atmosphere (400 parts per million), Ziska found that this increase in carbon dioxide resulted in a doubling of plant size. Now there are other contributors to spreading, such as the bird population and their dietary habits, but Ziska’s finding is certainly significant.
Poison ivy, by the way, is considered by some to be invasive, but it is certainly not alien to the area. The first history record of an unpleasant encounter with this plant was by John Smith in 1602!