I just extracted the plants bees foraged on in the Middle Ages/Medieval period from the book by Nicol Jacobi, written in 1568.
- white clover (Trifolium repens)
- cherry trees, especially Prunus cerasus
- preform of canola (Brassica rapa)
- poppies (Papaver)
- alder buckthorn (Rhamnus frangula)
- hemp (Cannabis sativa)
- vetches (Vicia)
- heath (Erica)
- honeydew from oaks and firs
- willows (salix)
- lime trees (Tilia)
It is highlighted in the book, that bees do not really thrive on flowering trees alone and they do often fail to store enough winter stores when there is nothing else than trees. Depending on the weather. The bees were placed near cultivated fields, especially with canola and hemp.
The so called "four-fields-crop rotation" was very common. That means different crops were rotated and one year nothing was cultivated on that field. "Greenfields" Those greenfields had a lot of white clover which was one of the main honey crops that time.
Most important crops: summer and winter canola, hemp and white clover.
Trees: lime trees and frangula.
There was litte honey to be made in the midst of deep woods. Also it was advised to lay out fields of vetches and white clover and canola just for the purpose of feeding bees on. Together with planting bee trees, which are fruit trees and frangula.
A lot of references in that book to beekeeping by the Romans, especially the beekeeping book by the Roman author Virgilius. The Romans did lay out fields for bees, too.
It seems the deep in the wood story of bees is simply a myth and bees were following humans for a long long time.
Title: Gründlicher und nützlicher Unterricht von der Wartung der Bienen
Author: Nicol Jacobi (and others)