Studies on Weed Management in Pastures

II. Distribution Pattern of Orchardgrass and Broadleaf dock (Rumex obtusifolius L.) in Newly Established Sward

Abstract

Competition among orchardgrass and R. obtusifolius plants, and plant performance in an orchardgrass sward were investigated in 1983 from the viewpoint of the distribution pattern of the plants expressed by the number and distance from neighboring plants which are represented by the I_δ index and Voronoi polygons.
The results obtained were as follows;
1) Invasion of R. obtusifolius into the orchardgrass sward resulted in a contagious distribution (Table 1, Fig. 1) of clumps consisting of a mixture of orchardgrass and R. obtusifolius plants.
2) The number of neighboring plants was the largest for orchardgrass close to both R. obtusifolius and orchardgrass clumps, as compared with orchardgrass close to an orchardgrass clumps only and R. obtusifolius close to both orchardgrass and R. obtusifolius clumps (Table 2).
3) Mean distances separating an orchardgrass clump (close to both R. obtusifolius and orchardgrass) from an R. obtusifolius clump of and another clump of orchardgrass were 7.51cm, 7.03cm, respectively. On the other hand, the distance separating a clump of R. obtusifolius from another R. obtusifolius clump was 6.10cm, and that between orchardgrass clumps close to an orchardgrass clumps was only 5.08cm (Fig. 3). The differences in the combinations of these neighboring plant species resulted in the difference in the distance between target plant species, which may account for contagious distribution mentioned above.
4) Invasion of R. obtusifolius decreased the population density of orchardgrass plants very close to R. obtusifolius shortly after sward establishment, but also promoted orchardgrass intraspecific competition resulting in a profuse growth of R. obtusifoius in the orchardgrass sward.
5) These results illustrate an example of competition for biological space between herbage and weeds. Further studies should be carried out to validate these data.