Interesting about the hazels, thank you Odsox. I learnt about the alder's nitrogen fixing this morning whilst googling different alders (no doubt we all have Black Alder as that seems to be the only European one).
I don't know whether my huge old alders were once coppiced because they all grow in big multi-trunked groups. Wish I could cut one or two of them for firewood cos that would keep us going for years

but unfortunately the chainsaw is not big enough and neither are we experienced (or mad) enough to even try!
One of the groups of trees is dead and is the local starlings' favourite roost. They really need to come down for safety reasons but they are a bit of a nightmare as no-one could climb up them as they are unsafe, they can't be felled because they are so tall they'd crush my fence and block the road, and the only alternative would be a cherry picker in my orchard which would involve it having to cross the ditch and we'd have to cut the fence, because the only entrance has an apple tree right in front of it. But that would trash my ground/grass plus I'm terrified of how much it would cost!!!