and second, there is a twofold difference We do not feel that we have confounded age with location in our studies. As we said, "we studied two adjacent abandoned hayfields," and "macroclimate and soil series are identical." Both fields were planted in timothy (Phleum pratense) and are slowly decaying into "natural" ecosystems characteristic of upstate New York. Since timothy is hardly a species characteristic of impoverished sites (1), we assume that whatever impoverishment leads to invasion of Poa compresa and Hieraciuim pratense arises out of the successional aging process. We have extensive soil data on the two fields as well as a description of their previous land usage from the land's owner. These data could not be included in a report in Science.
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