Changes in the Floristic Composition of Orchard Ground Cover in Relation to Light Conditions

Abstract

Floristic composition was studied from July to August in 27 stands of an orchard where weeds were uniformly managed by mowing but species, ages and training systems of trees were different among the stands (Fig. 1).
Interstand similarity was evaluated by the values of Euclidean distance,
D_jk=√Σⁿ_i=1(X_ij-X_ik)²
where j and k are the stands that are compared, i is the weed species under consideration and X is the score, frequency. Light intensity was found to significantly affect the interstand similarity, as illustrated in the constellation pattern shown in Fig. 2. Among the stands with weak shading the similarity was very high as compared with that among the stands with strong shading. The stands which belonged to the blocks of immature trees (2 to 4 years old), however, were markedly different although they were not shaded or exposed to limites shading. This phenomenon was mainly ascribed to the high dominance of perennial species specific to each stand (Fig. 3), presumably caused by the dispersal of vegetative-reproductive organs which was associated with the soil disturbance at the time when the trees were replanted.
The proportion of several species varied among the stands, depending on the light intensity gradient. As the light intensity increased, the coverage of Digitaria adscendens increased whereas that of Polygonum logisetum decreased (Fig. 3). Paspalum distichum appeared more frequently under lighter conditions, while Microstegium japonicum, Poa annua, Plantago asiatica and Oenanthe javanica were mainly found under darker conditions (Fig. 4).
Total coverage of C₄ plants tended to increase with the increase of the light intensity and was largely affected by the amount of D. adscendens (Fig. 5). The effects on the number of C₄ species were not as apparent as those on the coverage.