Effects of diversity and pattern on relative yields of four michigan first year fallow field plant species

Abstract

1. A study was designed to investigate the effects of intra and inter-specific competition on the productivity of single and multi-species stands of plants normally dominant in first year old-field communities of mid-Michigan. The four species used were Amaranthus retroflexus, Chenopodium album, Panicum capillare and Setaria viridis. 2. Specifically, we tested (1) the relationship between diversity and productivity, (2) the effect of arrangement (pattern) of individuals within an array of old-field dominants on yield and (3) the expression of dominance and resultant allocation of yields within mixture arrays of different plant species. In direct contrast to many earlier studies, our experiments were completed in the field under natural conditions. 3. Mean yield of the highest yielding monoculture, Amaranthus, was greater than any of the yields of the mixture plots. 4. Changing the pattern within mixtures had no significant effect on the yields of the mixture plots. Distribution of biomass among the component species followed a geometric pattern similar to that predicted by the niche pre-emption hypothesis (Whittaker, 1965, 1969). Using yield as a criterion, dominance was clearly expressed in the mixture plots. Amaranthus contributed more than 50% of the yield in all of the mixture plots. 5. A relative competitive ability index (RCA) was developed to demonstrate more clearly the intra and interspecific relationships among the species in mixture plots and to "equalize" the inherent weight differential among species. Relative Competitive Ability, from highest to lowest, was Amaranthus, Chenopodium, Setaria and Panicum. 6. The paired species experiment demonstrated that the performance of species in multi-species arrays cannot be predicted from paired competition experiments. 7. In the diversity-yield experiment and the paired-species competitive ability experiment, dicotyledons were clearly superior to monocotyledons.

Separating the chance effect from other diversity effects in the functioning of plant communities

“…Similar results are not an exception. For example, in a system similar to ours (fallow field, four species in monocultures and their mixtures), Kroh and Stephenson (1980) concluded that mixture yields were less than the highest yielding monoculture but greater than the lowest monoculture yield. Similar results were obtained by, e.g.…”

The biology of Canadian weeds. 130. Amaranthus retroflexus L., A. powellii S. Watson and A. hybridus L.

“…In Michigan, A. retroflexus had a greater competitive ability than Chenopodium album, Setaria viridis (L.) Beauv. and Panicum capillare L. in first-year fallow fields (Kroh and Stephenson 1980). Pearcy et al (1981), in a controlled experiment, showed that A. retroflexus was more competitive than Chenopodium album at high temperatures (35/28°C) because of the higher photosynthetic rates characteristic of the C 4 pathway.…”

The biology of Canadian weeds. 127. Panicum capillare L.

“…> P. capillare L. S. viridis is also a C 4 NADP-ME grass (see section 5a), but in a survey of weeds in Essex and Kent Counties in Ontario, Hamill et al (1983) found P. capillare in 8.2% of fields surveyed, with an "overall relative abundance" value of 4.1, whereas S. viridis was found in 42.6% of fields with a relative abundance of 18.1. Kroh and Stephenson (1980) also found P. capillare to be more susceptible to interspecific competition than to intraspecific competition. Although tillering is common, shading greatly reduces the numbers of tillers and panicles produced (Vengris and Damon 1976).…”

“…capillare appears to be a relatively poor competitor. Kroh and Stephenson (1980) determined relative competitive ability and ranked four weedy species as follows: Amaranthus retroflexus L. > Chenopodium album L. > Setaria viridis (L.) P. Beauv. > P. capillare L. S. viridis is also a C 4 NADP-ME grass (see section 5a), but in a survey of weeds in Essex and Kent Counties in Ontario, Hamill et al (1983) found P. capillare in 8.2% of fields surveyed, with an "overall relative abundance" value of 4.1, whereas S. viridis was found in 42.6% of fields with a relative abundance of 18.1.…”