PLANT COMPETITION IN RELATION TO NEIGHBOR BIOMASS - AN INTERCONTINENTAL STUDY WITH POA PRATENSIS

A standardized neighbor removal experiment was conducted in 12 plant c ommunities located on three continents to test the null hypothesis tha t competition intensity (CI) was independent of the amount of plant bi omass present. Six plots were chosen in each community to cover the ra nge of local variation in plant biomass. In each plot the relative gro wth rate (RGR) of transplanted Poa pratensis (Poaceae) seedlings was c ompared in the presence and absence of neighbors. Neighbors were remov ed experimentally using herbicide. Removing neighbors increased RGR of transplants significantly in most plots. CI increased with an increas e in the amount of neighbor biomass present in one community where the range of neighbor biomass was greater than in any other community. In contrast, CI did not change significantly with an increase in neighbo r biomass in other communities where the range of neighbor biomass was smaller. For the communities combined, CI was not related to neighbor biomass in a consistent fashion. These results indicate that competit ion may reduce growth over a wide range of habitat productivity, but t he relationship between CI and neighbor biomass may differ among commu nities.