Dynamics of the weed community in coffee plantations grown under shade trees: Effect of clearing

The florisüc composition of the weed community found in coffee plantations grown under shade-trees in Veracruz, Mexico, was studied in relation to canopy cover and the photoenvironment at ground level. Two well defined plant associations coexist in the weed community. One, in which Commelina diffusa and Impatiens walleriana are the dominant species, predominates in heavily shaded microhabitats. The other association is less shade-tolerant and has a greater diversity of species. After clearing the plantation, both associations disappear and a new weed association, in which perennial shrubs and subshrubs like Phytolacca purpurascens become the dominant species, gradually develops. Seed germination of the more abundant species in the new association is light-dependent. However, emergence of these species is not immediately triggered by clearing the plantation. Thus it is suggested that the weed community that develops after clearing old coffee plantations grown under shade-trees arises mainly from diaspores dispersed from neighbouring fields, and, to a lesser extent, from a persistent seed-bank.