Allelopathic Interactions Between Herbaceous Species and Trees Grown in Topsoil and Spoil Media

Dried foliage (litter) of several herbaceous species was mixed with either vermiculite or two minesoils (topsoil and spoil) in containers planted with black locust (Robinia pseudoacacia), white ash (Fraxinus americana) or sweetgum (Liquidambar styraciflrua) seedlings in a greenhouse. Also, germinated seed of northern red oak (Quercus rubra) was planted in containers previously seeded with herbaceous species. In vermiculite, black locust growth was inhibited by 12 g litter additions of ranger alfalfa (Medicago sativa), birdsfoot trefoil (Lotus corniculatus), tall fescue (Festuca arundinacea), and Kentucky bluegrass (Poa pratensis), but stimulated by red clover (Trifolium pratense) litter. White ash growth was strongly inhibited by alfalfa and trefoil added to vermiculite at 12 and 18 g levels. In topsoil, sweetgum was strongly inhibited by alfalfa litter. Both sweetgum and red oak grew poorly in spoil, but seeded perennial ryegrass (Lolium perenne), orchardgrass (Dactylis glomerata) and fescue grew well. Some aspects of red oak growth were inhibited if grown in containers seeded with alfalfa, ryegrass, orchardgrass, red clover or fescue. Although isolation and identification of allelopathic compounds was not attempted, these results demonstrate that there may be important allelopathic interactions between herbaceous species and trees planted on minelands.