Neighbour effects in the genus Avena. 2. Comparison of weed species.
The effects of the presence of a crop on weed growth were compared using Avena fatua, A. ludoviciana and A. sativa as weed indicator species and A. sativa and A. strigosa as crops. The effects of both crops on weed performance were essentially independent of weed density. A. strigosa depressed tiller number much more than panicle number and so caused a rise in apparent tiller survival. A. sativa depressed wt. of vegetative parts much more than wt. of panicles thereby causing an apparent rise in reproductive efficiency. The height superiority of A. fatua rendered it insensitive to interference from the crop when it was grown at low density. At the higher density it was almost as responsive as the other indicators. The reproductive efficiency of A. ludoviciana was increased by the presence of a crop.Canonical analyses and separation of variance components of the indicator responses showed that the species formed a series, A. sativa, A. fatua, A. ludoviciana, of increasing responsiveness of height to random variation in conditions between plots. A comparison of these species and also of A. strigosa showed that responsiveness to random variation at a between-plot level was not necessarily related to that at a within-plot level. See WA 23, 302. From summary.