COMPETITIVE EFFECT AND RESPONSE RANKINGS IN 20 WETLAND PLANTS - ARE THEY CONSISTENT ACROSS 3 ENVIRONMENTS

1 There is evidence that plants in natural communities form transitive competitive hierarchies, but the pervasiveness and malleability of hi erarchies remain controversial. We constructed three competitive ranki ngs among 20 wetland plant species in conditions known to be important in wetlands: a mesic, fertile environment, an infertile environment a nd a flooded environment. 2 Rankings were constructed using plants gro wn from seed in pairwise combinations for one growing season in an out door compound. The indicator species used to construct the rankings we re Carex crinita, Gnaphalium uliginosum and Lycopus americanus. The ot hers represented a wide array of morphologies, habitats and abundances and ranged from the large cosmopolitan Typha angustifolia to the smal l and rare Sabatia kennedyana. 3 Competitive rankings formed in all th ree environments. Competitive effect rankings based upon the results f or all three indicator species were significantly concordant across th e three environments (W = 0.59; P < 0.05), i,e. competitive effect did not change across environment. When calculated separately for each in dicator species, rankings across the three environments were significa ntly concordant for two of the three indicator species. Within any env ironment the ranking varied among the indicator species. 4 Rankings ba sed upon the mean competitive response to all three phytometer species were not concordant across the three environments (W = 0.35; P > 0.3) and were not concordant when calculated separately for each indicator species. Within any environment, response rankings were significantly concordant for two out of the three indicator species. 5 Competitive effect rankings tended to be constant across environments and were sen sitive to the kind of neighbour. Competitive response rankings varied across environments and were insensitive to the kind of neighbour.