The spruce and other local conifers (I live by the Bohemian Forest/Bayerischer Wald) have pollen that seems to be low allergenic by design. I know a lot of people who are allergic to birch or weed pollen, but not to spruce.
I read it as "breeds selected to be low-allergenic" by the relative orgs that I assume (re)planted them there but I have no real idea about german forests and the processes of planting trees there.
Different pollen have different weights. If you're seeing yellow dust laying on the ground then it's likely to be a heavy pollen that won't bother many people unless they actively stir it up. Example: People with pine allergies aren't really bothered unless they play in the pine needles and stir it up.
Not familiar with the biology of the matter. But I would assume there are advantages and disadvantages to the weight of the pollen in how it disperses and pollinates.