Here in the wild it pretty much blocks out any growth below it because it is so dense. It also has quite a bit of leaf litter and such that is stuck between the bushes themselves and that pretty much negates anything but the most aggressive growers
I planted Jerusalem artichokes on the NORTH side about 3' away from them to stop any grass encroachment..I have daylillies growing under them and some sunflowers growing in front of them.. I also grew 3 mulberry between my groupings of hazelnuts..(9)...but they are still babies but seem to be growing very well.
south of them a few feet i have seedless grape vines up and over an arbor..and 2 lilac trees and more jerusalem artichokes..therre is a path inbetween this group and the group of hazelnuts..that are kinda in an arched row...
these are on the north side of a circular lawn that has a ornamental red leaf cherry in the center and there are 4 beds surrrounding the lawn with paths around the outside of those ..you can see the map on my blog
Bloom where you are planted.
Find truffles in wild, plant compatible tree next to them(truffels are mycorrhizal). After a year or two move tree to your landscape and it should now be inoculated with truffle goodness. You can buy inoculated hazels online but almost everything I read about them claims little to no success. Best to find a truffle known to work well in your area for inoculation.