Bees collect pollen to feed to their brood. Without pollen, the brood starves and the bees are eliminated. In their native habitats, bees encounter a variety of plants with differing phenologies. Some flower early, some midseason and some flower late. Together, these plants supply a continuous source of pollen. In agroecosystems, as vast area may be cultivated with a single plant. For instance rape seed flowers early for a few weeks, then sets seed. It requires pollinators but only flowers for a few weeks. Bees can collect substantial pollen in spring only to starve in summer into fall.
However, if the agroecosystem is managed to include both blocks of rape seeds and blocks of sunflowers, the sunflowers will provide pollen after the rape seed is finished flowering. Borders and fence rows that contain flowering plants can provide a bridge food for bees if a gap occurs. Bees are an important component of food production. Plants with inadequate pollination will have lower yields. By managing the landscape to encourage bees, farmers can improve their yields and profits.