• Cultivating land for monocultural cropping systems usually leaves the soil
surface exposed for parts of the season, and thereby creates open Ecological
niches (empty ecological niches)
• Open ecological niches may occur in time (between harvest of one crop and
establishment of the next) and in space (between rows or beds until the crop has
closed canopy)
• Weeds emerge, grow, and reproduce in these open ecological niches—until they
are stopped by cultivation, pulling, mowing, herbicides, or direct competition
from crops