The allelopathic effects of Eucalyptus and Acacia plantations on the understory vegetation (Case study: Nourabad-Mamasani)

Afforestation with native or non-native species affects understory vegetation. These effects, besides of edaphic and climatologic factors, also depend on the species of the plants which are used. In the present study, the allelopathic effects of two species of Eucalyptus (E. camaldulensis Dehnh. and E. microtheca F.Mull.) and one species of Acacia (A. salicina Lindl) on the understory vegetation in Shiraspary region, Mamasani (Fars province) were studied. Aqueous extraction of leaves of these species was prepared in the laboratory; the effects of different densities of these extractions on the vegetative factors of Avena fatua L., Lolium perenne L., were investigated. The maximum inhibitory effect was on radical length and the minimum inhibitory effect was on seed germination. 5% density of these extractions had a stimulatory effect on the seed germination. The highest inhibitory effect on Lolium perenne was on E. camaldulensis, A. salicina, while the least inhibitory effect was on E. microtheca. The highest inhibitory effect on Avena fatua germination was on E. camaldulensis; the least inhibitory effect was after exerting A. salicina. 5% density of E. camaldulensis showed a stimulatory effect on radical growth. The 5% density of extractions increased the plumule length. The maximum inhibitory effect on the length of Lolium perenne was on A. salicina, E. camaldulensis, while the minimum inhibitory effect was on E. microtheca. The maximum inhibitory effect on length of Avena fatua was on E. camaldulensis, and the minimum inhibitory effect on radical length was on E. microtheca, A. salicina. The minimum inhibitory effect on plumule length originated from A. salicina. Compared with the control, the allelopathy effect of two Eucalyptus species was more than that of the Acacia. Both the stimulatory and inhibitory effects coincide with each other, indicating the presence of both types of allelochemicals which are capable of enhancing and suppressing at the same time. However, toxic allelochemicals are more volatile in nature than the stimulatory allelochemicals. This increased the competition ability of eucalyptuses and caused them to dominate forests and woodlands. Eucalyptus should not be cultivated in sensitive and especially arid ecosystems, so that the allelopathic effects of this species can be minimized.