Tree ID & Info

[xdcx]

Hi everyone

 

Please could you help me ID the 2x large tree's pictured? There was a good mix of small Rowan and Birch in among these with the ground being pretty boggy.

At largest measurement was 18" dia on the base cut for the tree on the right. Tree on left 15" dia.

I would have thought Poplar or Willow but would rather see what you guys think to put my mind to rest. 
Also the dark core I wasn't sure if this is normal and may depend on the tree. This was prevalent in even the smallest limbs and there was quite a lot of dead limbs. Is this dark center normal or does this look unhealthy to you? They were extremely fast growing but it may all make sense depending on what they actually are.

 

p.s. I am sorry if I come across a bit dumb to all of this. It is all new to me but I am very keen and doing my best to learn Thanks.

[Steve Bullman]

Yep def Poplar. Not sure which one, probably a hybrid black