There are so many articles and comments on the internet about beekeeping and efforts to "save the honeybees". Some of these involve buying a product with the assurance that a portion of the proceeds will go to honeybee research. That's a good enough thing but I tend to see it as more of a marketing tool for the businesses that do it rather than as a serious source of much needed funds.
Another kind of article encourages well meaning homeowners and gardeners to plant "bee friendly" plants in their backyards. While this is an admirable and kind thing to do, it goes much further toward providing habitat and forage for native pollinators; a just as important and not much recognized area of concern.
Planting "bee friendly" plants in the backyard won't do that much to directly help the honeybees. It's because of the way they search out nectar sources, report back to the other bees in the hive and focus on the most abundant source that is blooming at any given time.
Because of their numbers, forty to eighty thousand bees in the Spring and Summer, they need to produce a lot of food. That's why a backyard garden is nothing for a honeybee to write home about. Honeybees have evolved into very efficient foragers over the eons they have been on the Earth. Flying from flower to flower, backyard to backyard is energy inefficient. It requires too much flying for the nectar collected.
This is where trees come in. Nearly all kinds of trees produce flowers. Most of us don't see them, either because the flowers are not very prominent or because we just don't raise our heads up from the sidewalk or take a serious look out of the car window. Flowering trees are one of the most concentrated nectar sources available to honeybees. There are thousands of blooms on a mature tree. When the bees find a blooming tree they will work that tree until every flower has been visited several times. The distance from flower to flower is minimal, providing maximum foraging efficiency.
So, if you want to help the honeybees, you know what to do.
Here is a Wikipedia list of trees important for honeybees in the North of the U.S.
The above list left out one of the best tree types for nectar (and honey by the way) Linden trees also known as Basswood. http://en.wikipedia.org/wiki/Tilia#Uses