Ailanthus altissima
Allelopathy has been shown to play a crucial role in forests, influencing the composition of the vegetation growth, and also provides an explanation for the patterns of forest regeneration. The black walnut "(Juglans nigra)" produces the allelochemical juglone, which affects some species greatly while others not at all. The concentration of juglone by which the black walnut produces is not seen to have an effect on other plants. The leaf litter and root exudates of some "Eucalyptus" species are allelopathic for certain soil microbes and plant species. The tree of heaven, "Ailanthus altissima", produces allelochemicals in its roots that inhibit the growth of many plants. The pace of evaluating allelochemicals released by higher plants in nature has greatly accelerated, with promising results in field screening.