Here's a story about some of the effects of increased carbon dioxide and temperature on plants. At the end of the story they state:
It raises some questions about the impact on bees.The changing seasons may have both positive and negative effects. Dr. Morgan and his colleagues have found that the Wyoming prairie become more productive with an extra supply of carbon dioxide, for example.
On the other hand, Dr. Iler worries that the changing flowering times of plants may disrupt their pollination. Some species may end up competing with each other for visits from pollinating bees. “It’s reshuffling the community,” she said.