Filling the gaps (Hawthorns)

We have a road with hawthorns along the edge which have now become trees leaving big gaps. Any ideas on what to fill the gaps with or should we just plant more hawthorn? Has to be able to withstand a bit of wind too. TIA.

Can you not give the hawthorn a haircut to encourage it to thicken out at the bottom?
If not then any hedgerow plants would fill in nicely.

Hawthorn seems to self seed everywhere in my garden. Maybe there are seedlings in the gaps already?
SC's "topping idea is good - maybe they could be "layed" by cutting half way through the upright branches and bringing them down to meet the next hawthorn? Lots of Youtube stuff about Hedge laying for ideas.

Thanks for the hints! They are now too tall to give a ‘haircut’, unfortunately we’ve left them too long. Think just planting more will be the way to go.
No seedlings, ever, Veggie, no idea why that would be.

Thanks for the hints! They are now too tall to give a ‘haircut’, unfortunately we’ve left them too long. Think just planting more will be the way to go.
No seedlings, ever, Veggie, no idea why that would be.

You can coppice hawthorn, so it is never too tall to cut. You can take it right down to the ground, or whatever height is required, and it will happily regrow.
As for no seedlings, I believe the seeds germinate best if they have been through a bird first, so look in places away from the hedge where blackbirds in particular perch.

Depends how far apart the standing ones are, how low the branches are for laying and if you require this to be stock proof, just denote a boundary or somewhere in between.
If they're fairly close together and you have some decent uprights that are fairly straight you might get away with laying it. Remember that the sap needs to flow upwards so always make sure the cut is as low down as possible to allow you to keep the layed bit of hedge as close to the ground as possible but still running uphill.