Six species of herbs from the serpentine grassland of Jasper Ridge Biological Preserve (Stanford, California [USA]) Microseris sp., Plantago erecta, Micropus Californicus, Agoseris heterophylla, Layia platyglossa and Lasthenia glabrata.sbd.were grown individually and in competitive arrays, under three levels of CO2: 350, 500 and 700 .mu.l/l. CO2 affected the biomass of some species in the individually-grown plants but none in the competitive arrays. Here, in contrast to some previous studies, total community biomass was not significantly affected by CO2 in either condition. In every species where CO2 had a statistically significant effect on nitrogen content, higher CO2 resulted in lower nitrogen content. Competition appeared to decrease the effects of CO2. Our results suggest that in this community, competitive networks and adaptations to a low-resource habitat may strongly damp the effects of CO2. These results contrast with our previous work on annuals of a higher stature system and agree with recent results on Arctic tundra species.