>I don't have any of the answers, only more questions.  Why only male clones?
>Are they more productive of biomass than females?  I have not noticed that
>male willows are bigger than females.

I wasn't aware that willows were dioecious (separate male and female
plants, rather than both male and female flower parts on the same plant -
monoecious) but if there are male and female willow plants, it will be the
male that produces the pollen.  Female (only) plants don't produce pollen.
If a plant is monoecious, then you get both pollen and nectar (if plant
produces nectar, that is).  Most plants are monoecious.

Amy Thomson