Cutting back deciduous trees in May?

[Raera]

Just that really, is cutting approximately 2 metres off large whitebeam trees a good idea at this time of year?
Can't see any nests by the way.
Thanks

not a good idea now, no, as you'll likely end up with a sap run (as the tree is in an active growth period) and apart from looking ugly this can attract aphids and introduce disease into a healthy tree.

best to wait until the next dormant period in late Autumn/winter.

Thanks, that's what I'd read however my neighbour disagrees and wants it done now. They are my trees

@Raera I work with trees a lot (formerly in forestry) and you would actually be risking the entire tree by cutting into it now, as you'd essentially be creating an open and seeping wound that will definitely attract insects and could also let disease in.

Your neighbour will just have to wait, it's too late to do it this year! If they want to get professional advice, any tree surgeon registered with the Arboricultural Association will tell them the same thing...what you don't take is advice from some random "tree management co" with a chainsaw...

Thank you, I will ask about the Arboricultural Association.
I also worry that they are intending using a random chainsaw wielder.

Also, the birds are nesting...

It might even be against regulations. (Where I live the cutting season is very clear and you would be fined for breaking the rules)

My neighbour has just had a tree cut. He's not a gardener and I think was quite taken aback by how hard it was cut. (He wouldn't know about sap runs and aphids) . I know there were no birds nesting.

Given it is done , is there anything he could do to mitigate the damage. ?

@BasiliskStare your neighbour will be best just waiting for the tree to mend the cut itself...depending on what type of tree it is, it might be fine (they can be amazingly resilient) or if it's something more delicate then it might struggle. But he needs to let the tree sort itself out - you can buy "wound salves" for bark but they actually interfere with trees' natural processes, so can do more harm than good. The trouble is, any idiot can buy a chainsaw, and the damage is done all too quickly...

Speaking as someone who knows a bit about arboriculture...

It is the wrong time of year, for a number of reasons I won't bore you with, some of which are mentioned upthread, and a couple more are below.

It is far better to prune deciduous trees when they are not in leaf, so that branches can be selectively removed without ruining the shape of the tree. You can't see what to do when there are leaves all over it. The winter image of a deciduous tree that has been unsympathetically butchered is horrible.

Another reason this time of year is a poor choice, is that the tree has just exerted every last reserve of energy in producing all those leaves, and has not yet begun to store up more energy via photosynthesis to promote new growth of both new branches and roots. Pruning just after a tree has come into full leaf will severely weaken the tree, the effects of which will be felt for some years and can even be fatal. As my stupid neighbours once found out when they did exactly that to a beautiful rowan in their garden (against my advice, but it was their tree).

Many thanks all, I've told the neighbours it can't happen before November x