I find tree identification difficult, although I am trying to learn "new ones". For the rabbits I tend to stick to the ones which are growing in the garden and so I am therefore confident about the ID. Willows I find are a particularly diverse group and I struggle to identify common ID features. It's helpful to catch them at the catkin stage.
I have tried to find reliable websites that (a) help with tree ID and (b) indicate whether a tree is rabbit safe in all its parts. (a) is not so difficult. I tend to use Wiki and this one
http://www.woodlands.co.uk/blog/tree-identification/. For (b) I check the tree against the list in this site
http://kanin.org/node/190 and if it's not within their list I tend not to look much further and don't feed.
Sometimes the information given in websites for what is rabbit-safe is very unreliable I find (especially opinions from people on other forums). Take the Hazel/Beech situation for example. I think the leaves you have been feeding j&b and also the ones Kara posted a pic of yesterday are Beech. Beech does not feature on my Kanin.org list. Also when I checked a couple of other sites one said it was unsafe, another said that the leaves were OK but the bark not and then another said that both leaves and bark were OK. After MM posted to say that both Hazel and Beech were safe, I re-checked using more sites and found that the majority of sites I visited said that the leaves were OK. That is not good enough though because we know that many sites will simply copy information from one site to another.
I think what this calls for is a second RWAF funded publication by Parsnipbun on rabbit-safe tree leaves/bark
So where does this leave us? I think Beech is almost certainly safe (MM could you let us know what source you used to determine this please). I agree with your ID of White Poplar and Silver Birch w and s from looking at websites, but I don't know these two very well IRL. As to whether they are safe or not, well they are both on my Kanin.org list, but I don't know whether all Poplars are safe. I have this niggle that Black Poplar is not :?
Yes, it's great that so many people are looking at this thread